A few weeks ago Phil Nelson put me in touch with the owner of this nice Dumont RA113. He and his brother grew up with this set and he really wanted to get it restored to working condition.

Although I've plenty of other projects, I agree to take a break from them and work on it. They pulled up in front of my place with it yesterday afternoon.

I removed the chassis while it was out on the curb to lighten the load but the cabinet was still quite heavy.

The set had been kept inside it's whole life and is in very good condition. The finish looks very similar to my blonde Sentinel so it's probably also made from Korina wood. As best they can remember it is working when retired from service.

There's a ding on both cabinet sides from the door handles whacking into them. Seems they should have used a little bumper like on Zenith portholes.
http://farm4.staticflickr.com/3797/9806782264_3fb34f7df2_z.jpg (http://www.flickr.com/photos/70039806@N00/9806782264/) http://farm6.staticflickr.com/5522/9806849673_a37dfd6a7c_z.jpg (http://www.flickr.com/photos/70039806@N00/9806849673/) http://farm4.staticflickr.com/3743/9823586324_6e17290f7d_z.jpg (http://www.flickr.com/photos/70039806@N00/9823586324/)

The CRT had been replaced with a Westinghouse 17BP4B back in the late 50s and the set saw very little use afterwards. Even so I was surprised at how quickly it showed emissions well into the good with excellent cutoff and rock solid life test.
http://farm6.staticflickr.com/5522/9806774445_f3f34d9d48_z.jpg (http://www.flickr.com/photos/70039806@N00/9806774445/) http://farm3.staticflickr.com/2887/9806860293_7ff35d739d_z.jpg (http://www.flickr.com/photos/70039806@N00/9806860293/)

The tube chart shows a 17AP4. The back does not have a cutout for the CRT but luckily the 17BP4 just fits.
http://farm4.staticflickr.com/3673/9806862033_b3088ba450_c.jpg (http://www.flickr.com/photos/70039806@N00/9806862033/)

The chassis is rust free and quite clean :)
http://farm8.staticflickr.com/7426/9806822266_42047d182b_z.jpg (http://www.flickr.com/photos/70039806@N00/9806822266/) http://farm6.staticflickr.com/5486/9806823236_1bdb52e69b_z.jpg (http://www.flickr.com/photos/70039806@N00/9806823236/) http://farm8.staticflickr.com/7426/9823613895_92b2b88ba5_z.jpg (http://www.flickr.com/photos/70039806@N00/9823613895/)

I see a few replaced caps but it's mostly original.
http://farm4.staticflickr.com/3803/9806808344_036bd90905_c.jpg (http://www.flickr.com/photos/70039806@N00/9806808344/)

It also appears that a HV anode lead has been spliced it. Perhaps the original 17AP4 had a different type of HV cap ?
http://farm3.staticflickr.com/2825/9806798935_4eb6d1dbc1_z.jpg (http://www.flickr.com/photos/70039806@N00/9806798935/)

I love seeing other RA-113's!

This one is a pretty example.

I've had to hold off on the restoration of my mahogany DuMont for now, but will be getting back on it during the winter, when I don't like going outside very much. I had to find a power transformer for mine, but thanks to a great internet friend, it was located, so that major hurdle was overcome.

I look forward to seeing progress on this set as it is brought back to life, :thmbsp:

Hi Bob,

Very nice find! It looks exactly like the one I'm beginning to restore. I, too thought it was a "Burlingame" but I now believe that it is a blond version of the "Revere." Mine is model number RA-113-B4. I'm just in the process of putting together a cap order. (It's the one I picked up in Kenosha last month for $55.) Here are a few photos:
http://i1216.photobucket.com/albums/dd366/IsthmusTV/RA-113_8_zps95b190b3.jpg (http://s1216.photobucket.com/user/IsthmusTV/media/RA-113_8_zps95b190b3.jpg.html)
http://i1216.photobucket.com/albums/dd366/IsthmusTV/RA-113_9_zpseb25fc2b.jpg (http://s1216.photobucket.com/user/IsthmusTV/media/RA-113_9_zpseb25fc2b.jpg.html)
http://i1216.photobucket.com/albums/dd366/IsthmusTV/RA-113_6_zps083b149c.jpg (http://s1216.photobucket.com/user/IsthmusTV/media/RA-113_6_zps083b149c.jpg.html)

My CRT is the original DuMont 17AP4 which tests good. Should be a fun restore. Good luck!

-Clark

Hi Bob,

Very nice find! It looks exactly like the one I'm beginning to restore. I, too thought it was a "Burlingame" but I now believe that it is a blond version of the "Revere."...

Right you are. I didn't notice the difference in legs when I looked at the models on Phil's website (http://antiqueradio.org/DuMontRA-113Television.htm).

It's not my set though - I'm restoring it for someone. I did consider going for the set you got but it's much too big for my place. The sooner I get this done and out of here the better :yes:

I wouldn't have guessed it beforehand, but that cabinet's attractive in blonde.

I think the RA-113 is an interesting & fun set to restore -- enjoy!

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Very nice sets. I have a much rougher one around here some place I've been working on. Will be fun to watch you guys restore these :)

17AP4 was a metal cone wasn't it ? if so that would explain the splice because you would have to change the anode to fit a 17BP4

mike

It also appears that a HV anode lead has been spliced it. Perhaps the original 17AP4 had a different type of HV cap ?

The anode connection on the 17AP4 looks the same. Mine has a quick disconnect inline with the anode lead (as does Phil's). It looks like that was removed on that set. You can see one end of it hanging in this photo. And the 17AP4 is an all glass CRT:
http://i1216.photobucket.com/albums/dd366/IsthmusTV/RA-113_10_zps517ab038.jpg (http://s1216.photobucket.com/user/IsthmusTV/media/RA-113_10_zps517ab038.jpg.html)

I noticed that the focus control on mine looks pretty bad (green corrosion on the element wire). I haven't tested it, but I preemptively ordered the same replacement Phil used from Surplus Sales of Nebraska since I know these are a common failure point.
http://i1216.photobucket.com/albums/dd366/IsthmusTV/P1030117_zps32c7026a.jpg (http://s1216.photobucket.com/user/IsthmusTV/media/P1030117_zps32c7026a.jpg.html)

It's not my set though - I'm restoring it for someone. I did consider going for the set you got but it's much too big for my place. The sooner I get this done and out of here the better

I hear ya, these suckers are big. I'm not quire sure where I'll put mine yet :scratch2:

I'm very fortunate to be restoring a set that now two masters, Phil and Bob, are blazing the trail!

-Clark

Those are some very nice blondes! Usually the finish is all beat to heck on the blonde stuff.

I think it's because they used an actual light hardwoord rather than "limed oak" type finish.

I finally have the chassis up on the workbench. First I'm going to pull the 5U4 rectifier and power it up to make sure the power transformer is OK.
http://farm8.staticflickr.com/7444/10638895425_87c7739705_c.jpg (http://www.flickr.com/photos/70039806@N00/10638895425/)

http://farm3.staticflickr.com/2891/10639361333_13139e457b_c.jpg (http://www.flickr.com/photos/70039806@N00/10639361333/)

Do you guys think this ASC 1,000 pF, 10kV cap is a suitable replacement for the original 500p HV caps ?
http://farm6.staticflickr.com/5535/10638916336_80c6286de1_c.jpg (http://www.flickr.com/photos/70039806@N00/10638916336/)

it might work , I used 470pf caps from moyer that were 10kv or 15kv that are round in similar applications and they worked.

mike

Do you guys think this ASC 1,000 pF, 10kV cap is a suitable replacement for the original 500p HV caps ?
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When most rebuilders got a 17AP4 dud, they would rebuild it as a 17BP4 or, if they could aluminize, as a 17BP4B, since as these newer types were more marketable and used the same bulb.

Since the maximum external coating capacitor on a 17AP4 was 500 µµF greater than on the replacement 17BP4, you are still within factory specs on the HV to ground capacity in the CRT circuit. This is the capacitor that you sometimes hear warnings not to increase due to the potential shock hazard.

Increasing the other two 500 µµF 10KV capacitors to 1000 µµF would allow the second HV rectifier to operate more efficiently, but the tiny HV increase and extra loading on the HV output tube and Flyback should be minimal.

I'm impressed by how beautiful the insides of that set is!

Jas.

Thanks for the info. I'm also considering using some ceramic HV caps as they are a lot less expensive.

The power transformer is good and the tuning eye is showing signs of life :)
I get some HV with the old caps still installed, but it's definitely less than it should be. I expect new caps will take care of that.
http://farm4.staticflickr.com/3703/10641854545_5442924ef3_c.jpg (http://www.flickr.com/photos/70039806@N00/10641854545/)

Making steady progress with the recap. Those old caps are very sticky and gooey :yuck:
http://farm8.staticflickr.com/7323/10711995074_82b6bb817e_c.jpg (http://www.flickr.com/photos/70039806@N00/10711995074/)

Making steady progress with the recap. Those old caps are very sticky and gooey :yuck:

The caps in mine were all gooey, too. I had to use Boraxo to get the gunk off my fingers :sigh:

Looking good, Bob. I'm curious to see how the ceramic caps work in the HV doubler.

-Clark

Thanks. The ceramic caps and a few others parts I needed arrive tomorrow. With a bit of luck I'll try firing it up later that night or on Saturday.

Crap! I just missed the Fedex guy and he left a tag saying another attempt would be made on Monday :( I've been using Fedex for years they've always left the package somewhere on the property if no one answered the door.

Bummer. Maybe it's a new driver. Here in Madison, they give you the option of picking up the package after 5:00 PM on the day of the attempted delivery. I live only 4 miles from their depot, so I have done that on occasion. But in Chicago, it's probably way out in the burbs somewhere.

I finally took a closer look at the tag and realized the depot was only a couple miles away and open to 9:30pm on a Friday night so I got my parts after all :)

Here are the 500pF, 15kV ceramic caps I'm going to try.
http://farm8.staticflickr.com/7316/10752565784_e116b7399c_c.jpg (http://www.flickr.com/photos/70039806@N00/10752565784/)

Cool. I have a feeling they'll work just fine in this application.

Are those the Vishay Cera-Mite 615R Series? If so their data sheet lists them for TV and Monitor applications. Nice to know someone is still looking out for us. :thmbsp:

East Paterson changed their name to Elmwood Park a few years ago. That town is about 10 miles from my mom's.
http://farm4.staticflickr.com/3673/9806862033_b3088ba450_c.jpg
Paterson NJ is a real dive, so this town didn't want that association anymore...:thumbsdn:

Are those the Vishay Cera-Mite 615R Series? If so their data sheet lists them for TV and Monitor applications. Nice to know someone is still looking out for us. :thmbsp:

They sure are :yes:

I'm not sure what to do about this resistor. It's R268 and is in series with the 6BG6 HOT grid. The schematic and parts list show 100 ohms but this is a 47 and appears to be original. When I measure it, I get 98 ohms.

It seems to me that if it really is twice what it should be, it could reduce the 6BG6 drive and flyback output. Should I leave it alone since it's close to the 100 specified in the service info, or replace it with a new 47 ?

http://farm6.staticflickr.com/5474/10787440486_75c8115098_c.jpg (http://www.flickr.com/photos/70039806@N00/10787440486/)

My chassis has a 100 ohm in there(looks original), so apparently yours should be fine. Sams schematic shows a 47 ohm(with see note). Note 6 on parts list says some models use 100 ohm. :) I think it's purpose is to damp out parasitic oscillations, so it's probably not super critical on value. You see those used on audio outputs too.

During my 21CT55 restoration I found that SAMs showed the production changes of later sets than the RCA schematic showed, so the 100 ohm may have been a production change in later sets. I guess you need to decide if you want to restore it to original condition or incorporate the production changes. Is that 47 ohm resistor discolored, like it has been getting way too hot? That would explain why it measures high. If so, I would replace it with another 47 ohm resistor of higher wattage.

Dave

No, it's not discolored - just dirty. I guess I'll leave it alone and see how it plays.

Here's another head scratcher. This section of the candohm resistor R282 B measures about 5300 but the schematic shows 2140. I've seen plenty of candohms go open but not drift in value that much.

Perhaps it's another production change ? What does the Sams show ?
http://farm3.staticflickr.com/2824/10789375184_89d55ee1bb_c.jpg (http://www.flickr.com/photos/70039806@N00/10789375184/)

Sams says 2140. You're measuring out of circuit?

Nuts, I guess I'll have to bypass it. Yes, I measured it out of circuit.

Scratch that - I didn't fully take it out of the circuit after all. Now I get 322K so it's probably corroded or partially burned out inside. There's no wattage specified in Riders but I suppose 25W should be good enough.

Sams lists each section at 10 watts.

Thanks. I figure I should replace both sections while I'm at it. I think 1500 and 2200 should be close enough to the original 1480 and 2140.

I managed to get the yoke and FC off so I can try it out on the workbench with a test CRT. There's clearly a weld where it was rebuilt and the yoke was reluctant to slide over that portion of the neck. Some slow careful rotating back and forth did the trick.
http://farm4.staticflickr.com/3724/10811432695_f3b5a1d88c_c.jpg (http://www.flickr.com/photos/70039806@N00/10811432695/)

Good, I'm glad you were able to get the yoke off. I'm not going to mess with mine until the 17AP4 gets tired, which will probably be years from now.

BTW, that 25K resistor in the horizontal output was toast on mine, too. I also initially mistook it for a paper cap.

Looking forward to seeing you fire it up on the bench with a test CRT!

-Clark

I'm not sure what to do about this resistor. It's R268 and is in series with the 6BG6 HOT grid. The schematic and parts list show 100 ohms but this is a 47 and appears to be original. When I measure it, I get 98 ohms.

It seems to me that if it really is twice what it should be, it could reduce the 6BG6 drive and flyback output. Should I leave it alone since it's close to the 100 specified in the service info, or replace it with a new 47 ?

http://farm6.staticflickr.com/5474/10787440486_75c8115098_c.jpg (http://www.flickr.com/photos/70039806@N00/10787440486/)

I would change the resistor! It already changed value and will progressively get worse.
I see some Allen-Bradley five percent resistors used. :scratch2:

OK, I'll put a good 47 in there. Are you referring to the 5% resistors in the upper-right ? I guess Dumont used better quality parts than their competitors. I'm finding very few that need replacing :)

OK, I'll put a good 47 in there. Are you referring to the 5% resistors in the upper-right ? I guess Dumont used better quality parts than their competitors. I'm finding very few that need replacing :)

Some of the Admirals, of the time were using German and Japanese resistors, connected in parallel and series, to get the proper values needed.
The German resistors had the flat leads.
I read somewhere that there was a parts shortage during the Korean war. :scratch2:

I've worked on a couple early 50s Admirals with resistors like that.

I took a closer look at the anode lead and discovered two splices with a piece of line cord between and the rubber cap is falling apart! That's all going to be replaced :yes:
http://farm8.staticflickr.com/7434/10832687545_5c07355634_c.jpg (http://www.flickr.com/photos/70039806@N00/10832687545/)

. . . . I took a closer look at the anode lead and discovered two splices with a piece of line cord between and the rubber cap is falling apart!

Whooah! And 3M Gasket cement used in place of Corona Dope!

Back in the day, before air-conditioning, we used to see a lot of this from shade tree mechanics who tried to stop arcing on the anode connector due to high humidity. Usually, it took a razor blade to scrape off the mess and doing that destroyed the connector in the process.

Jas.

I dove inside the HV box last night and found more evidence of old repairs.

All three HV caps had been replaced. They used "pigtails" with pointy leads sticking out rather than plunging the ends into the solder cups. Not the proper way to dress HV connections :no:
http://farm4.staticflickr.com/3716/10839582345_72a520f164_c.jpg (http://www.flickr.com/photos/70039806@N00/10839582345/)

One of the 2.2 ohm filament resistors had cracked so I replaced them both.
http://farm8.staticflickr.com/7454/10839922733_61ed59e67a_c.jpg (http://www.flickr.com/photos/70039806@N00/10839922733/)

More evidence of past HV troubles.
I think this Micamold cap is 0.001 mfd @ 500v and the white dot indicates it's really paper inside so I'm going to replace it.
http://farm4.staticflickr.com/3666/10839645766_46ef1c655c_c.jpg (http://www.flickr.com/photos/70039806@N00/10839645766/)

I think this Micamold cap is 0.001 mfd @ 500v and the white dot indicates it's really paper inside so I'm going to replace it.


Oops, I didn't replace that cap in mine, I thought it was a silver mica. I'll make a note to replace it the next time I pull the chassis.

I also chose not to pigtail the HV caps. Getting the solder to pool just right in the cups was a bit of challenge, though. I found it best to orient the chassis so that the solder cup I was working on was horizontal, otherwise gravity causes too much of the solder to spill out.

Looks like you're getting close to the first power-up.

Oops, I didn't replace that cap in mine, I thought it was a silver mica. I'll make a note to replace it the next time I pull the chassis.

There's still a chance it is. I'm going to test and dissect it to see what's really in there.

...Getting the solder to pool just right in the cups was a bit of challenge, though...

I flipped the chassis upside down to get the first one to pool properly.

The Dumont service info lists that cap as a mica so I'll leave it alone after all.

I finished up work inside the HV box including a new 40kV anode lead.
http://farm6.staticflickr.com/5549/10883008576_942fa5469a_c.jpg (http://www.flickr.com/photos/70039806@N00/10883008576/)

United Electron 1X2 tubes. I don't think I've seen this brand before :scratch2:
http://farm6.staticflickr.com/5481/10882969395_980cafcd08_c.jpg (http://www.flickr.com/photos/70039806@N00/10882969395/)

Here's a link to AK that'll probably tell you more than you ever wanted to know about United Electron tubes. Sounds like they were one of those dime store brands.
http://www.audiokarma.org/forums/showthread.php?t=179305

What size and type of wire did you use for the anode lead?

Thanks for the link. 20 AWG 40kV wire salvaged from a more modern TV

I salvaged a nice anode cap from an Admiral then continued work under the chassis.
http://farm8.staticflickr.com/7441/10917740354_e16f836efd_c.jpg (http://www.flickr.com/photos/70039806@N00/10917740354/)

Better take a look inside this box.
http://farm8.staticflickr.com/7343/10917658436_39cefc3f2b_c.jpg (http://www.flickr.com/photos/70039806@N00/10917658436/)

Yep, two more paper caps and some resistors almost double the resistance they should be.
http://farm8.staticflickr.com/7436/10917656836_ed941f8564_c.jpg (http://www.flickr.com/photos/70039806@N00/10917656836/)

... and some resistors almost double the resistance they should be.
http://farm8.staticflickr.com/7436/10917656836_ed941f8564_c.jpg (http://www.flickr.com/photos/70039806@N00/10917656836/)

"Now there's a surprise!" Glad you checked Bob. But, I was sure that you did.

What was a little surprising is that all the larger valued resistors (10K and up) were within spec. It's the smaller (< 500 ohm) resistors that were way off. I've seen the same in some early Admiral sets.

What was a little surprising is that all the larger valued resistors (10K and up) were within spec. It's the smaller (< 500 ohm) resistors that were way off. I've seen the same in some early Admiral sets.

The failure mode of most carbon composition resistors is moisture absorption - the carbon particles absorb moisture, causing the particles to separate, and forming a higher resistance bond. It's noticed more greatly in small, sub 1K values, as the shift is tens or hundreds of ohms, a large percentage of the original value. This is typical whether on the shelf, or installed in equipment.

No manufacturer was ever able to eliminate moisture as a problem. IRC tried, and got a patent for their "molded" carbon composition resistor process that sealed the outside of the resistor and thus reduced moisture intrusion, but aging and lead flex allowed the moisture intrusion.

If it wasn't for economy and pulse/surge capability, carbon composition resistors would have been dead long ago, as most film types suck at handling surges.

And no, you can't bake the moisture out - DoD and NASA both tried, but found that the heating process shifted resistance greater than the moisture did.

Cheers,

I recently purchased some carbon comps from Allied Electronics for those "special" sets where I'd like to retain the original look. Also, they were dirt cheap :)

Check out the bag they came in.
http://farm4.staticflickr.com/3796/10939227463_c63c0e51b6_c.jpg (http://www.flickr.com/photos/70039806@N00/10939227463/)

Along with the 1/2w 100K resistors inside was this humidity strip and some silica gel desiccant.
http://farm3.staticflickr.com/2883/10939103784_ebc0ece678_c.jpg (http://www.flickr.com/photos/70039806@N00/10939103784/)

It seems to have helped. Every resistor is +/- 5% with a bunch being under 100K.
http://farm8.staticflickr.com/7442/10939303943_b9deb02793_c.jpg (http://www.flickr.com/photos/70039806@N00/10939303943/)

I spot checked a few from my non-environmentally sealed stash and all are high but still just within tolerance.
http://farm8.staticflickr.com/7395/10939102244_c593617d4d_c.jpg (http://www.flickr.com/photos/70039806@N00/10939102244/)

Those same two resistors (68 Ohm and 270 Ohm) were way high in mine, too. I have also had to replace very few resistors in this set. I see that you also had only two paper caps in the little shielded compartment. Phil Nelson's had three:scratch2:
http://i1216.photobucket.com/albums/dd366/IsthmusTV/DuMont%20RA-113/P1030379_zps7b7df925.jpg (http://s1216.photobucket.com/user/IsthmusTV/media/DuMont%20RA-113/P1030379_zps7b7df925.jpg.html)

-Clark

Before I forget, would you mind taking a quick shot of the tuner string when you get a moment? On the one I'm doing, it seems to have slipped, and the knot came out of place on the shaft.

I finished replacing the main power supply filter caps which just leaves two multi-section caps to go. I figure that was good enough and decided to fire it up.

No smoke and I could hear the horizontal kick in. No raster though. I loosened up the anode cap and was able to draw a nice strong arc.

Eventually, I noticed that the test CRT filament wasn't lighting up and touch up the pins with a soldering iron. That did the trick :)

Unfortunately, I only seem to have horizontal deflection and I can heard some corona arcing inside the HV box but it's progress of sorts.

http://farm4.staticflickr.com/3830/11004200335_c4cffa2f00_c.jpg (http://www.flickr.com/photos/70039806@N00/11004200335)

http://farm6.staticflickr.com/5514/11004296996_17f00c8948_c.jpg (http://www.flickr.com/photos/70039806@N00/11004296996)

Before I forget, would you mind taking a quick shot of the tuner string when you get a moment? On the one I'm doing, it seems to have slipped, and the knot came out of place on the shaft.

Does this help ?
http://farm8.staticflickr.com/7364/11004432343_2b2aca1768_c.jpg (http://www.flickr.com/photos/70039806@N00/11004432343)

Sort of. The string has a knot which fits into the center. I need to see which way it wraps around the shaft....clockwise or counterclockwise from the center, out.....

I think I'd need to remove the dial face to show that part ? Not so easy to do.

Nope, just pull off the knob and give me a shot showing where the dial cord goes when it comes off the center of that geared shaft :)

Do these help ?

http://www.flickr.com/photos/70039806@N00/11018689726

http://www.flickr.com/photos/70039806@N00/11018600645

http://www.flickr.com/photos/70039806@N00/11018846204

http://www.flickr.com/photos/70039806@N00/11018773616

Look at the second stringing diagram (page 6-8) in the Rider manual for RA-112:

http://www.earlytelevision.org/pdf/dumont-ra-112-rider-tv6.pdf

I believe that's what I looked at when I restored my RA-113. My tuner had a busted gear, so I had to pull the mechanism completely apart, and somehow I got it back together correctly.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

The vertical oscillator definitely isn't running and I've got some weird voltage readings on the osc tube. The plate is -55 volts but should be 70 :scratch2: Could be the boosted B+ line isn't working right.

I discovered a loose wire in the B+ Boost circuit. Fixing that resulted in a raster :)
http://farm3.staticflickr.com/2864/11024335026_656832046d_c.jpg (http://www.flickr.com/photos/70039806@N00/11024335026)

I rigged up a crude antenna and picked up this LPTV broadcast. The focus is terrible because the focus coil messes up the self focusing 8XP4 test CRT.
http://farm4.staticflickr.com/3755/11024335956_1ee031f6cd_c.jpg (http://www.flickr.com/photos/70039806@N00/11024335956)

Hooked up to an ATSC receiver / converted box. Zero audio. However, the FM radio reception is pretty good. It wouldn't be the first time a vintage TV didn't like my converter box.
http://farm4.staticflickr.com/3725/11024454703_78238da007_c.jpg (http://www.flickr.com/photos/70039806@N00/11024454703)

I dug out an unmarked, rebuilt 17" CRT and hooked it up.
http://farm4.staticflickr.com/3735/11024338496_1e05b7f2c7_c.jpg (http://www.flickr.com/photos/70039806@N00/11024338496)

This is the best focus I could manage. Could be this CRT isn't compatible with this set or maybe the focus circuit needs some work.
http://farm4.staticflickr.com/3675/11024406464_8397b7c854_c.jpg (http://www.flickr.com/photos/70039806@N00/11024406464)

Thanks for the pics and reference materials. I got it :)

Seems that the tuner was rewound incorrectly at some point, and the tensioner was stuck on the tuner shaft. Working now!

One question, just need to know where to set the dial pointer.

With the control turned completely counterclockwise, where should the pointer be at?

The middle of '13'. That reminds me that have some tuner issues. I tune in channel #4 around the '3' and can;t get channel #3 at all. I figure a LO trimmer needs to be adjusted.

It's coming along nicely, Bob. If you want to use the test CRT, I wouldn't worry about removing the focus coil from the yoke assembly. It was pretty easy to get the coil back to where it needed to be after I replaced mine. You could probably mark the spring-loaded screws to streamline the process.

The focus is terrible because the focus coil messes up the self focusing 8XP4 test CRT.As IsthmusTV noted, temporarily removing the focus coil from the yoke gives a nice sharp picture with an 8XP4.

Phil Nelson

http://antiqueradio.org/art/DuMontRA-113FocusCoilRemoved.jpg

http://antiqueradio.org/art/DuMontRA-1138XP4BenchSetup.jpg

Wouldn't it just be easier after recapping and all the tests done, to put the chassis back in the cabinet and use the set's picture tube? I mean I can see doing this if you run into issues at that point, but doing all of this to me seems like a lot of added work.

I'm on the electrolytics in my RA-113 right now. I'm doing them one-at-a-time, and reinstalling the chassis enough to hook up the CRT and speaker after each part group is replaced. So far, so good.

On these sets, we are lucky that the chassis is designed to be removed from the set easily, and has that nice big opening in the frame for repairs. Many sets have NO help for us.

I went ahead and removed the focus coil which took care of the focus issues. Occasionally, I get a little tearing but it's certainly watchable.
I can't push the yoke all the way into the CRT bell though so it's not filling the screen.
http://farm8.staticflickr.com/7392/11055026946_fcc360c4e2_c.jpg (http://www.flickr.com/photos/70039806@N00/11055026946)

Now as for sound I switched, to using a BT modulator set to channel 5 for an RF source and finally got some good strong sound.
Only problem is that it was miles off from the video. So much so that the screen is blank when I have sound. I tried yet another brand of modulator with similar results.

So much as I'd like to avoid it, I'm going to attempt an alignment - at least on the sound. The alignment instructions in the Dumont and Rider service info and rather complex and involve clipping pins off tubes!

Perhaps the Sams alignment procedure is a bit easier. Does anyone have a scan ?

Forgive the format, but here they are :)

****

I have a PDF of the SAMS for the RA113. Can email to you.

Thanks guys. I was struggling with numerous differences between the Riders and my set - even the tube lineup is somewhat different. The Sams appears to be a much better match.

They also specify using a clipped 6AK5 though so I guess I'll just sacrifice one. Not exactly the rarest of tubes anyway.

I went ahead and removed the focus coil which took care of the focus issues.

I'd keep the focus coil if it's being used as a power supply choke. Add extending wires to the coil and mount it at some distant point (away from the CRT) in the cabinet, maybe near the bottom back. So it's available if you or a subsequent owner wants to use it on another CRT.

Now as for sound I switched, to using a BT modulator set to channel 5 for an RF source and finally got some good strong sound.
Only problem is that it was miles off from the video. ...

So much as I'd like to avoid it, I'm going to attempt an alignment - at least on the sound.

Is this a set with an independent sound IF, and not an intercarrier set? You might be able to "walk" the sound IF alignment to the frequency needed to get good sound when a good picture is tuned in. Note the direction you need to leave good sound towards a good picture, and put it back to good sound, and adjust it again back to the direction for good picture, but not completely losing the sound, and tweak the sound IF trimmers to get good sound. Repeat until you are where the good picture is tuned. Then adjust the ratio detector or such to get the DC bias is correct.

I meant I just removed it from the neck of the CRT - it's still connected electrically. It's not used as a choke though. They have two dedicated chokes mounted under the chassis for the power supply.

Yes, it's split carrier sound. I'm going to jump right the sound alignment portion. If that doesn't work out, I'll start at the beginning.

How are you guys feeding a signal into these DUmonts sets ? They have what looks like an RCA jack which I think is around 75 ohms impedance. All I have handy is a standard composite video cable and an RCA to F converter at the other end for the RF modulator. It works OK, but I'm sure there's a better way to do it.

http://farm4.staticflickr.com/3716/11057694293_26702799ba_c.jpg (http://www.flickr.com/photos/70039806@N00/11057694293)

How are you guys feeding a signal into these DUmonts sets ? They have what looks like an RCA jack which I think is around 75 ohms impedance. All I have handy is a standard composite video cable and an RCA to F converter at the other end for the RF modulator. It works OK, but I'm sure there's a better way to do it.


I was lucky to have a male "RCA" to female "F" adaptor that I acquired at some point over the years, so I use that. I don't think I have another one, but I'll check. If I do, you're welcome to it.

The picture looks quite good. I hope the sound alignment goes well. Mine was close enough that I just tweaked it a little by ear.

-Clark

I bought one of those somewhere not that long ago, maybe three years ago when I got my RA-109. Check your local ma and pa hardware store.

I muddled my way through the alignment procedure over the last couple nights and things are looking better. I still get double peak sound on the dial, but it's louder and clearer. So is the picture.

The response curves for two of the stages were complete garbage. Way off frequency and the wrong shape. I was puzzled by a little jumper wire on the bottom of one can feeding from a lug into a little tube. That wire had been clipped off the IF can to the left.
http://farm8.staticflickr.com/7300/11109483676_9330ca65ef_c.jpg (http://www.flickr.com/photos/70039806@N00/11109483676)

Eventually, I found a section on this in the service info. I'm guessing some service tech encountered this problem and made an attempt to fix them.
http://farm6.staticflickr.com/5549/11113687046_c1df961c2e_o.png (http://www.flickr.com/photos/70039806@N00/11113687046)

I was able to adjust the wire and slugs in the right side coil and get a reasonable response curve. For the other I tacked on a 2pF (the closest I had to 1.5pF on hand) mica cap and got a semblance of the proper response.

I'll track down a couple proper 1.5pF caps and realign. So far I only found a ceramic C0G cap at Mouse for about $1.75 each.

Evan as is, the picture is pretty darn good.
http://farm4.staticflickr.com/3784/11113608404_58f6b3b59d_c.jpg (http://www.flickr.com/photos/70039806@N00/11113608404)

I do have some horizontal jitter though. I still need to get a scope on the horizontal lock coil and go through the adjustment procedure. Hopefully that will clear it up.
http://farm3.staticflickr.com/2853/11113559835_0fdedb3ddb_c.jpg (http://www.flickr.com/photos/70039806@N00/11113559835)

My RA-113 had an intermittent horizontal blip similar to that.

http://antiqueradio.org/art/DuMontRA-113HorizontalBlip2.jpg

http://antiqueradio.org/art/DuMontRA-113HorizontalBlip1.jpg

The source was a bad mica coupling cap. Details at the section titled, "Curing the Horizontal Blip:"

http://antiqueradio.org/DuMontRA-113Television.htm#HorizontalBlip

There may be other causes for horizontal hijinks, of course :)

Your picture looks very good already.

Regards,

Phil Nelson

Those pics of horizontal issues with the guy's face distorted out towards the ladies sort of remind me of the way the eyes bug out on the wolf characters when attractive women are around in some old Tex Avery cartoons....

Thanks for the tip Phil, I'll check that resistor out. While on your website, I also read up on the operation of the 6AL7 eye tube and I must say mine does not behave that way at all!

One side is fixed at about 3/4 but the other side operates in the opposite way it should. When no station is tuned in, the bottoms of the two bars are level. When a station is tuned in, the left side bar is at it minimum :scratch2: The 3.3K resistor in the socket has drifted up to about 4.3K but I don't think this would account for the odd behavior.

http://farm4.staticflickr.com/3760/11122069165_5e69dbf320_z.jpg (http://www.flickr.com/photos/70039806@N00/11122069165)

Good call Phil - that 180pF mica cap was leaky as a sieve. All I had handy was a 200pF, but it seems to be working fine. That makes me wonder if others might be bad as well :scratch2:

I turned on my RA-113 to observe the indicator and it does behave as described in the manual. When the tuning is centered, with best picture and sound, the bars are more level than not.

The schematic shows a 1 meg resistor (and a couple of paper caps) connected to pin 4 of the 6AL7 indicator tube. Might be worth checking that resistor, too.

Phil Nelson

Thanks, I'll take a closer look at that indicator and the tuner. Something is just not quite right with the tuning action.

Don't want to change the focus of this thread, but I sure wish I had this much luck on mine. First power up today after the recap. Full static audio, no reception on anything, just an incomplete white line on the screen. More work for another day :)

I don't know about luck. I've been working on it daily for about a month ;)

I've found that sets like this one that were kept by the original owners and used for years and years are the worst to restore. Aside from numerous repairs, parts start to wear out. If I can't sort out the tuner issue soon, I may just leave it as is.

I've got a hunch the tracking is off between the individual sections of your inductuner. I don't see how the local oscillator being off would cause that kind of double tuning. The local oscillator only beats against whatever frequency the tuner is in resonance with. The local being off would cause everything to be shifted up or down on the dial.

I received this comment on YT that I think explains why I'm receiving the output of my converter box at two points. I do not have this issue when tuning the commercial LPTV channel 6 broadcast.

That leaves a couple issues. The audio tuning in at two point very close together (one just at the edge of good video and one with bad video) and the odd eye tube indicator. Same issue when tuning in FM radio.

I've aligned the audio several times and it looks perfect to me. I'm going to go through and test the few mica caps in the audio IF and maybe go through the alignment one more time.

That buzz and poor reception of your converter box when you tune low is when you are tuning the lower sideband of the signal. An analog signal is fed into the video modulator with the video signal at baseband and the audio signal at 4.5 MHz. What comes out is an AM signal, with consumer equipment this is sent straight to the set. With Broadcast or cable equipment all by 0.75 MHz of the lower sideband is filtered out. With digital the signal is fed into an 8 Level modulator and again all but 0.75 MHz of the lower sideband is filtered out. This is called vestigial sideband. VSB as it is known is used to allow some redundant information (to make receiver filtering easier) and the use of the carrier (to eliminate the need for a touchy BFO or product detector) to receive what is almost a single sideband signal. If brodcasting used true AM the signal would be 10 MHz wide with VSB the signal is 5.75 MHz with a .25 MHz guard band prior to the lower sideband.

You could try an older DVD/VHS machine with built in rf modulation.

I guess I really did get lucky with mine. The IF alignment seems pretty good, as does the alignment of the IndcTuner. (Or is it an InpuTuner?) I think Phil's speculation is correct. That since it still has a strong original 17AP4, it was probably pushed aside decades ago when it quit for some other reason and not run into the ground.

It looks to me like the 6AL7 is driven by one plate of the 6T8 discriminator through a low pass filter. So it's an indication of the audio carrier strength ? Since my audio isn't tuning as expected, I guess it follows the indicator would behave oddly.

It looks to me like the 6AL7 is driven by one plate of the 6T8 discriminator through a low pass filter. So it's an indication of the audio carrier strength ? Since my audio isn't tuning as expected, I guess it follows the indicator would behave oddly.

Sounds right. I wonder if it's possible that the output of your disc. transformer was inadvertently wired in reverse at the factory? I'm not even sure if that would do it, but it seems odd you're getting a signal inversion to your eye tube.

I also noticed a note in Sams saying some models have L23,L24 reversed. Not sure how that would effect the alignment process.

Did you ever figure out why the sound trap(A13) was not working in the tuner? That could account for some dependencies seen during alignment.

No, but I've seen the same issue with traps in other sets and it was always a faulty mica cap. I'm not too keen on opening up that tuner and extracting the trap to find out.

I'll trace out the eye tube wiring as soon as I can. I'm way backed up at work right now from the holidays.

I stayed up late and gave the sound IF and good going over. Right away I noticed a 1K resistor with a crack that measured about 300 ohms. The one to the right of it measured 1,300. Both got replaced.
http://farm6.staticflickr.com/5529/11184599444_75f20b994e_z.jpg (http://www.flickr.com/photos/70039806@N00/11184599444)

Next came the mica caps. 3/5 were bad - a 10pF, 27 pF and 47pF. By 'bad' I mean they were showing leakage at less than 200 volts (all are rated for 500) and I couldn't get a capacitance reading. Hopefully, replacing these will have a positive impact on the sound tuning.

http://farm4.staticflickr.com/3706/11186335574_77da306a20_z.jpg (http://www.flickr.com/photos/70039806@N00/11186335574) http://farm4.staticflickr.com/3804/11186334806_d6ef350bda_z.jpg (http://www.flickr.com/photos/70039806@N00/11186334806)

I finished replacing the leaky mica caps and out of tolerance resistors including the one in the eye tube base then redid the audio alignment. Bingo! :banana:

The eye tube now responds like it should, I only get good sound at one distinct point on the dial per station and it coincides with a sharp picture.

Time to start putting this set back together :yes:

Good show, Bob! Congratulations. After spending more time tuning around with mine, I notice that I also have the double peak issue with the audio. It's not as pronounced as yours was, but clearly I still have some work to do. I'll start by looking at those mica caps.

Are you going to do anything to the cabinet? I haven't done anything to mine except superficial cleaning.

Again, congratulations. Your friend should be very pleased.

-Clark

Congratulations is right. I still don't understand how those bad components would cause the reveres action you were getting on the eye tube. Suppose it was a combination of the leaky caps which caused a false alignment indication at multiple resonances. Was the alignment off a lot when you went back through it? At any rate I think we're about to the point in time that we need to start shotgunning all mica caps. Although sometimes those types of caps make for a excellent learning experience.

Congrats, Bob! I just watched your YouTube video last night on this set. Nice to see that you solved the audio issues and the tuning eye reverse issue. Cannot wait to see the next video of this set functioning! :)

we're about to the point in time that we need to start shotgunning all mica caps.Micas can go bad and I have replaced my share of them, but many more in sweep circuits (horizontal, vertical) and HV circuits. Audio circuits tend to be more forgiving, but if you find a bad one -- or two -- there, of course it has to go.

I would not advocate shotgunning micas in IF stages unless you are well equipped and well versed in alignment, since a slight change in lead dress may kick things out of whack. Ditto, even more so, for the tuner section. Service manuals often included warnings to keep your clumsy mitts out of the tuner.

These days I look on mica caps as I do resistors. Generally more reliable than the hopeless paper caps, but not immortal. If a basic (paper + electrolytic) recap doesn't magically fix everything, then the next phase is to look at micas + resistors. One thing that I do during the basic recapping phase is test every component on the same terminal where I am connecting a new cap, the theory being that if I'm disturbing (unsoldering & resoldering) anything on that terminal, I may as well deal with everything at once to avoid trashing the connection with repeated monkey-wrenching. That way, I naturally uncover some other bad parts as I go, although it's not very systematic.

Phil Nelson

... Are you going to do anything to the cabinet? I haven't done anything to mine except superficial cleaning.

Again, congratulations. Your friend should be very pleased.

-Clark

Pleased and relieved as I really want to get back to my other projects :yes:

I'm not going to touch the cabinet but the owner asked for suggestions on preserving the finish. I'm no expert on blonde finishes but I figure a quality, non-silicone furniture polish found be fine.

Congratulations is right. I still don't understand how those bad components would cause the reveres action you were getting on the eye tube. Suppose it was a combination of the leaky caps which caused a false alignment indication at multiple resonances. Was the alignment off a lot when you went back through it? At any rate I think we're about to the point in time that we need to start shotgunning all mica caps. Although sometimes those types of caps make for a excellent leaning experience.

Yes, the IF between the 1st & 2nd audio stages was off as was the discriminator. Those are the areas where I replaced three micas and several resistors.

I would call it a reverse action - more like the bias point was shifted over so that the left bar would never dip below the reference bar. Now, it swings to either side. I'll show that in detail in the next video up later today.

Congrats, Bob! I just watched your YouTube video last night on this set. Nice to see that you solved the audio issues and the tuning eye reverse issue. Cannot wait to see the next video of this set functioning! :)

That video was my first attempt at alignment. I'll post another video later today showing the replaced micas and second alignment with the correct tuning eye action and sound.


Micas can go bad and I have replaced my share of them, but many more in sweep circuits (horizontal, vertical) and HV circuits. Audio circuits tend to be more forgiving, but if you find a bad one -- or two -- there, of course it has to go.

I would not advocate shotgunning micas in IF stages...

I agree and didn't touch the tuner. Also the micas in the video IF tested OK so I left them alone. It was tempting to replace them all, but that would require yet another alignment plus those micas get expensive! Also, there's always that risk of slipping with the soldering iron and damaging a coil or other fragile component.

I think the big culprits were the bad 10pF coupling mica cap between the 1st and 2nd audio IF stages and the two bad 1K resistors which threw the bias off the 2nd tube.

Yipee! Great going! Look forward to seeing the video.

I've wondered on some of these sets if the reason a bunch of components are bad is because of some kind of power surge or jolt to the system in the past? Something like lighting coming in the ac line or antenna lead. Maybe even running long time on low voltage or other abuses?

Perhaps that doesn't explain it as much as plain old age and normal wear and tear. And, maybe that couldn't affect these mica caps. But, I see some people's restorations with a bunch of normally good components that have gone bad and think they all got zapped by something instead of just coincidence.

Just wondering out loud here (or through a keyboard).

I was thinking more along the lines of an issue with the materials or construction technique used. All the failed caps are "Micamold" - not exactly know for being high quality.

I have to agree that shotgunning the mica caps could be a bad idea. I keep forgetting that not everyone wants to get involved with alignment. Although in a few more years it may come down to that. Even so it would be best to replace them one at a time, testing as you go.

I reinstalled the yoke, speaker and chassis and fired it up. Well that's a little disappointing. Moving the ion trap magnet all around the neck has barely any effect. I brought it near a screwdriver and it seems plenty strong. I'll dig up some spares and give it another try.
http://farm3.staticflickr.com/2831/11293817315_1f09040201_c.jpg (http://www.flickr.com/photos/70039806@N00/11293817315/)

I consulted the Rider service info and they mention this specific issue. It seems that he original 17AP4 required a stronger magnet than the 17BP4. They suggest sliding the original all the way back over the base.
http://farm4.staticflickr.com/3731/11295167405_a5f537c90a_c.jpg (http://www.flickr.com/photos/70039806@N00/11295167405/)

That did the trick :) I'll try to find an RCA to F connector at Radio Shack tonight so I can feed a cleaner signal into it.
http://farm6.staticflickr.com/5507/11295168475_dccf7ba5e7_c.jpg (http://www.flickr.com/photos/70039806@N00/11295168475/)

While working on this issue, I would occasionally hear a loud squeal from the HV area. Eventually, I tracked it down the the HOT plate lead. Moving that wire just slightly on the end going into the cage can eliminate or bring back that squeal. I suspect that's why there's tape wrapped around it - to keep it from moving. I guess I'll pull the chassis again and take a closer look. Probably a bad connection at the flyback or a break inside the wire.
http://farm8.staticflickr.com/7395/11295283083_c288fa6579_c.jpg (http://www.flickr.com/photos/70039806@N00/11295283083/)

Congratulations on getting a picture on your set CRT! It is looking great, to me.

I finished replacing the leaky mica caps and out of tolerance resistors including the one in the eye tube base then redid the audio alignment. Bingo! :banana:

The eye tube now responds like it should, I only get good sound at one distinct point on the dial per station and it coincides with a sharp picture.

Time to start putting this set back together :yes:

As i mentioned sometime back on your You-Tube video, Bob, i learned a long time ago to just go ahead & replace all them postage stamp (Mica) capacitors because they can & will fail. after many years of lack of use, moisture & humidity can get inside of them & contaminate the Silver Oxide (or whatever electrolytic material) they use for a dialectric. it amounts to the same thing as Silver Oxide Migration that is common to I.F. cans. back then, the technology just was not there to manufacture a perfectly sealed capacitor. those Micamold capacitors were not really much better then paper capacitors, especially in Humid envirements.

Overall, I've had pretty good luck with them still being good. If they weren't so expensive I might be inclined to replace them more often.

I thought I traced the source of that squealing to this wire arcing to this resistor, but nope. After replacing it and touching up the solder joints in that area I can still get it to squeal if I position that HOT lead just right. Even so, it's easy enough to secure it such that there's no squeal so I'm calling it good enough unless someone has a suggestion.
http://farm6.staticflickr.com/5494/11303503816_5b87de5593_c.jpg (http://www.flickr.com/photos/70039806@N00/11303503816/)

After a long session of fighting with the trap magnet, focus coil and yoke, I got the picture centered and focus fairly well. Just in time to catch on of those butchered "Sixth Sense" Night Gallery episodes. They're actually not bad when seen in their original 50 minute run time.

http://farm3.staticflickr.com/2846/11303505196_7cd1278df5_c.jpg (http://www.flickr.com/photos/70039806@N00/11303505196/)

There's a faint, bright vertical bar on the far right you can just make out in this shot. I've seen them on the left before, but not the right :scratch2:

I'll get a pattern generator hooked up and see if it goes away if I adjust the drive and linearity controls.
http://farm8.staticflickr.com/7291/11303472125_8f8b80cf84_c.jpg (http://www.flickr.com/photos/70039806@N00/11303472125/)

It looks great, Bob. I think you can call this one done. I doubt the owner would even notice the vertical band on the right side (I also have never seen one on the right side of the picture). But hopefully the drive control will take care of it.

As for the squealing in the HV cage, mine also has electrical tape wrapped around the HOT plate lead. I haven't heard squealing from mine but I wonder if this was an issue with this set :scratch2:

I ordered a bunch of Twilight Zone DVDs that I plan to watch on the DuMont over the holidays.

-Clark

After sleeping on it, it occurred to me that the plate lead is in series with that 68 ohm resistor so there's no potential difference to cause any arcing between them.

What I think is more likely is that the wire is stressing the phenolic board and flyback.

The CRT isn't quite as bright as I expected considering it tests like new and is aluminized. Perhaps that's because the HV is only 12kV for the original 17AP4 while a 17BP4 typically sees 14kV.

After sleeping on it, it occurred to me that the plate lead is in series with that 68 ohm resistor so there's no potential difference to cause any arcing between them.

What I think is more likely is that the wire is stressing the phenolic board and flyback.


there could also be the possibillity that where the wire enters the cage (without the tape wrap) that there may be a "capacitance" issue, where the wires insulation is acting like a dialectric, especially where the wire itself is touching the metel on the HV cage, hence, the reason for the tape wrap.
that added capacitance can throw the waveform off, causing the squeal.

After sleeping on it, it occurred to me that the plate lead is in series with that 68 ohm resistor so there's no potential difference to cause any arcing between them.

What I think is more likely is that the wire is stressing the phenolic board and flyback.

The CRT isn't quite as bright as I expected considering it tests like new and is aluminized. Perhaps that's because the HV is only 12kV for the original 17AP4 while a 17BP4 typically sees 14kV.

Your CRT is aluminized? I don't think you should need an ion trap, then.

Re. the low brightness, have you tried tweaking the brightness range a bit? Ie., shifting resistance(s) a bit to nudge G1 slightly more positive relative to the cathode?
Hard to be more specific without seeing the schematic.

there could also be the possibillity that where the wire enters the cage (without the tape wrap) that there may be a "capacitance" issue, where the wires insulation is acting like a dialectric, especially where the wire itself is touching the metel on the HV cage, hence, the reason for the tape wrap.
that added capacitance can throw the waveform off, causing the squeal.

There's a large hole cut out of the metal cage where the wire enters and it's supported by a piece on phenolic insulator. The squealing seems to come and go depending on the angle and pressure of the wire inside the box. It will be clearer in the next video I post.

Your CRT is aluminized? I don't think you should need an ion trap, then.

Yes, it's an aluminized 17BP4B. The probably used a bent gun to avoid confusion because the 17BP4, 17BP4A and 17BP4C are not aluminized.

Re. the low brightness, have you tried tweaking the brightness range a bit? Ie., shifting resistance(s) a bit to nudge G1 slightly more positive relative to the cathode?
Hard to be more specific without seeing the schematic.

No, I haven't messed with that. If I turn the brightness up all the way now, the picture will get washed out. Here it is in a brightly lit room. I guess it's not that bad after all.
http://farm3.staticflickr.com/2824/11314729303_31c9bd9734_z.jpg (http://www.flickr.com/photos/70039806@N00/11314729303/)

I hooked up a pattern generator and fought with the settings some more. The linearity is better now and the bright line is gone from the right side. The have the width switch and coil set for minimum, but still just a bit too wide. Not that any would notice.

So I'm finally calling this one done :)
http://farm8.staticflickr.com/7289/11316528313_d30a3cf2fd_z.jpg (http://www.flickr.com/photos/70039806@N00/11316528313/) http://farm8.staticflickr.com/7318/11316455336_4a8b691bee_z.jpg (http://www.flickr.com/photos/70039806@N00/11316455336/)

It's tough to get a good shot of the cabinet while the set is playing.
http://farm4.staticflickr.com/3801/11316487384_a36927b925_c.jpg (http://www.flickr.com/photos/70039806@N00/11316487384/)

Very, very nice. The owner should be tickled pink!

Excellent. I remember having a devil of a time getting the image focused and positioned without shadows, etc., on my RA-113. It would have been easier if I could have pushed the yoke & focus coil just a wee bit closer to the front. I theorized that my rebuilt 17BP4 had a slightly different profile to the CRT bell than the original CRT. It's hard to imagine they would have had to struggle like that in the factory.

Phil Nelson

There's a large hole cut out of the metal cage where the wire enters and it's supported by a piece on phenolic insulator. The squealing seems to come and go depending on the angle and pressure of the wire inside the box. It will be clearer in the next video I post.


Ok, Now it's clear to me. it appears that ether the hardware that holds the flybacks ferrite core together might be loosening up or has developed a crack in the core itself. you might want to check the two nuts that hold the core together to see if they are loose.

unfortunately, due to changes to You-Tube, i cannot make any comments on any post anymore because they screwed something up. even though i have a G+ account, the You-Tube Commenting does not work any more for me.

unfortunately, due to changes to You-Tube, i cannot make any comments on any post anymore because they screwed something up. even though i have a G+ account, the You-Tube Commenting does not work any more for me.

I noticed something screwy was up too. They are currently trying to force me to change my username to my actual name, or I can't comment. Seems very strange. Suppose I could open a new account using my old username as my real name. :D

Great job on the DuMont, Bob.

Just out of curiosity - are you convinced that this set has a better picture than any other decent set of the period?

Well, I've definitely seen better pictures on earlier sets, but I think it's better than the few other 1951-52 sets I've restored.

Here's the bandwidth of this set which peters out around 3.5 MHz (2nd bar from the right). Now to be fair I wasn't able to align it as well as I'd have liked due to a couple funky IF transformers.
This also illustrates how the width was too great before I squeezed it down.
http://farm4.staticflickr.com/3665/11319632635_a2a8feaf1f_z.jpg (http://www.flickr.com/photos/70039806@N00/11319632635/)

Here's an RCA 630TS where you can distinguish lines out to 4.5 MHz
http://farm4.staticflickr.com/3783/9618202041_c6d2920676_z.jpg (http://www.flickr.com/photos/70039806@N00/9618202041/)

Hi Bob,

I just reviewed the Dumont RA-113 videos on YouTube. That was quite an experience. I suppose if a set is over-engineered, more things can fail.

On the sets I fiddled with years ago, there was always a coil that would adjust for the audio and video separation that allow one to sync up the tuning. These were sets from the early to mid sixties. Basically it shifted the band where the audio would be fetched from. One tuned the best video and then adjusted the coil for the best audio - no fuss, no muss.

While you were wrestling with the IF strips, I couldn't help but think there was something wrong with the tuner local oscillator alignment(s) which might account for the difficultly in tuning the best video and the best audio at the same spot.

I get confused with the setting of IF frequencies and always run back to AM radio alignment experiences to keep myself straight. In an AM radio, the alignment can be done without using exact frequencies. I seem to remember tuning the local oscillator for 540 KHz (tuning cap closed) on the dial. And then the oscillator trimmer cap for 1600 KHz (tuning cap open). It didn't really matter exactly what the IF frequency was, as long as it was peaked. The point is that things could be approximately on frequency and all was well.

Of course, with old TVs, there are two bands, audio and video which have to be calibrated together. Given the over-engineered nature of that Dumont set, I am wondering if there are two separate mixers, one for video and one for audio. I am wondering if the two slugs that were on the Dumont tuner were for this.

Is this a crazy idea? Two mixers?
Would they allow the IF frequencies to be off a bit as long as the IF strips were tuned accordingly.

Anyway, in all these musing I find myself wondering what exactly is critical in TV alignment, and what really has to be matched to what.

Also, because the audio is FM (wider than AM), maybe the audio IF needs to be stagger tuned as well. Would stagger tuning of the audio IF allow less critical station tuning with respect to audio. Would the bandwidth of the ratio detector accommodate this? I wonder how much of the detector slope is actually used.

Steve

It's really not over engineered. Take a look at any RCA or Admiral from the same year and they're pretty much the same. What you experienced were sets with inter-carrier sound where both video and audio go through a common IF. The audio is picked off after the detector and a trap keeps it out of the final video stage.

This set uses a separate IF for video and audio like many sets of the late 40s - early 50s. Here the audio trap is right after the tuner and two are amplified independently.

The reason I had so much trouble with aligning the set was bad mica caps and damaged video IF transformers. I wish I could have replaced them, but spare parts are hard to come by these days.

...In an AM radio, the alignment can be done without using exact frequencies. I seem to remember tuning the local oscillator for 540 KHz (tuning cap closed) on the dial. And then the oscillator trimmer cap for 1600 KHz (tuning cap open). It didn't really matter exactly what the IF frequency was, as long as it was peaked. The point is that things could be approximately on frequency and all was well.

Actually if the IF is incorrect in a broadcast band AM radio, it will cause the tuning range on the main dial to be either too wide or too narrow.
Its being 'approximately' correct is probly good enuff in most cases. :scratch2:
In a TV with split IFs, you definitely want the sound IF to be correct for the sound to track correctly with the pic.

Hi Old Coot,

I'm talking 5 maybe 10 Khz here. I must try a mathematical analysis some day. I know I set the local oscillator to the low end and tuned the trimmer at the high end, so the dial was set correctly. Let me give this a think.

Bob,

I never worked on a double IF strip set. I hope the engineer who came up with the single strip got a good raise that year. Did you try turning those two adjustments on the top of the tuner?

-Steve
(old fart)

Bob,

In "Admiral 24C16 restoration part 5 (we have sound!)" at 3:30, you adjust a coil on the tuner which fixes the audio problem. Specifically, it adjusts the output IF frequency of the audio band to properly go through the audio IF stage which you just aligned. You do not re-adjust the fine tuning of the station and presumably the video remains clear (the video IF strip still gets what it needs from the tuner output, frequency-wise).

How can this be without two mixers in the tuner? See my previous post about two mixers.

Steve

Bob,

I never worked on a double IF strip set. I hope the engineer who came up with the single strip got a good raise that year. Did you try turning those two adjustments on the top of the tuner?

-Steve
(old fart)

Some of the early, low end sets used a single strip like the Motorola VT-71. I'm pretty sure most used dual IF so they could use amplifiers best suited for wideband AM (video) and narrowband FM (sound).

No, I didn't touch the tuner.

Bob,

In "Admiral 24C16 restoration part 5 (we have sound!)" at 3:30, you adjust a coil on the tuner which fixes the audio problem. Specifically, it adjusts the output IF frequency of the audio band to properly go through the audio IF stage which you just aligned. You do not re-adjust the fine tuning of the station and presumably the video remains clear (the video IF strip still gets what it needs from the tuner output, frequency-wise).

How can this be without two mixers in the tuner? See my previous post about two mixers.

Steve

I wasn't as knowledgeable about Admiral tuners back then. I'm pretty sure that was the oscillator trimmer capacitor. So all I was doing was shifting the LO frequency a bit - same as adjusting the fine tuning. The passband of the tuner is huge (over 5MHz) with the video and audio carriers being 4.5MHz apart.

Ah. So the local oscillator for the channel frequency(ies) was off more than the fine tuning could accommodate?

Yes, I think so. Here the response curve of a typical tuner. Ideally, one hump is the sound carrier and the other the video carrier. That's how you get away with one mixer. The response is wide enough to include both, but not so wide it picks up adjacent channels.

http://farm9.staticflickr.com/8522/8599089568_46422616c7_c.jpg (http://www.flickr.com/photos/70039806@N00/8599089568/)

Got it.

I wonder is there a way to show the bandwidth of the tuner? Can you sweep across, say, channel 3 frequencies with any of your signal generators? That might be an interesting trace, and a way to check tuner performance.

I do not know how low the levels are coming out of the tuner. -60dB? But maybe the input signal could be pretty hot to boost it a bit. One might need a sensitive spectrum analyzer for this test.

Steve

The marker blips in the photo are 4.5 MHz apart. If I went out to the -3db point it would be around 5.5 - 6.0 MHz bandwidth.
Sure, I have sweep generators that can cover that easily. I can already tell you what you'd see though. It would be the image above squeezed horizontally.

Squeezed or stretched? The tuner output has to be at least as wide as the IF strip. You wouldn't need the IF skirts so much if the tuner were set at 6 MHz wide. Maybe I am misunderstanding your meaning.

Actually, the tuner could be very wide, say 18 MHz. The IF strip just picks out a 6 MHz window as the tuner slides the spectrum back and forth in front of the IF window.

I have seen sets actually tune to adjacent stations when the fine tuning is adjusted far off to the extreme ends of its range. That means that three channels can come through with the channel selector is set to one channel.

This doesn't necessarily mean that the bandpass of the tuner is very wide. But with a good IF, there isn't a need to design tight passbands into tuner mixers and tuner RF amps. I suspect this is the cheapest way to build a tuner and IF strip combination. And it explains why there is rarely a need to re-align a tuner. It is so wide that it doesn't ever go out of spec as part drift out of tolerance. And it explains why the IF strip is so critical. The tuner doesn't do anything to limit the bandwidth. The IF does all the work.

Food for thought.

Steve

I wish you had a pricey spectrum analyzer that could look at the raw tuner output.

I meant if I expanded the width sweep generator the response curve would become squeezed on the scope. All I can tell you is that in all the late 40s TVs I've worked on the tuner had about as wide a response as the IF.

I'm not sure what would be gained by a spectrum analyzer that you can't see with a sweep generator and scope.

Hi Bob,

You have measured this before? Awesome. What did you use to look at the tuner output / IF input? Is your scope that sensitive??

Steve

Well yes, that's what the photo is above - the actual response curve of a tuner.
I connected a sweep generator to the antenna terminals with proper termination and connected my scope to a test lug they provide on the tuner. It's all explained in the alignment instructions. Any decent scope will have enough sensitivity.

That being said, it's not something I recommend messing around with. It's very easy to screw up the tuner and they rarely need adjustment.

Well yes, that's what the photo is abov...

That being said, it's not something I recommend messing around with. It's very easy to screw up the tuner and they rarely need adjustment.

That is for sure. Very few (NO) places to send a tuner for repair/alignment anymore from what I have heard. I guess the biggest problem is contacts making proper contact ;)

Well yes, that's what the photo is above - the actual response curve of a tuner.
I connected a sweep generator to the antenna terminals with proper termination and connected my scope to a test lug they provide on the tuner. It's all explained in the alignment instructions. Any decent scope will have enough sensitivity.

That being said, it's not something I recommend messing around with. It's very easy to screw up the tuner and they rarely need adjustment.

A touch up of the mixer plate coil is sometimes indicated in the IF alignment instructions.

Well yes, that's what the photo is above - the actual response curve of a tuner.
I connected a sweep generator to the antenna terminals with proper termination and connected my scope to a test lug they provide on the tuner.

Does the tuner have a detector in it?? I am thinking it should look something like this with the largest output centered on the middle frequency to the IF, lower frequency on the left and increasing to the right.

No, you wouldn't align a tuner or IF like that. Scopes back in the 40s didn't have the bandwidth to directly observe the IF waveforms. The oscilloscope is connected to a grid leak bias network on the mixer.

You can download the service info here. It covers the circuit theory and alignment instructions. There are also books on ebay covering vintage TV servicing and alignment if you'd like to learn more. http://www.earlytelevision.org/pdf/admiral_20a1_rider_tv4.pdf

Hi Bob,

The manual for the Admiral 20A1 was very helpful. In the description of the RF section there is mention of a trap for "adjacent channel picture rejection." There are also several caps for alignment and setting a bandwidth. You are right. The tuner bandwidth is adjusted for one channel. The full skirt of the tuner RF response curve in Figure 32 (page 15) is over 10 MHz wide, but the tuner 3 db down points are about 6 MHz apart. The station channels are 6 MHz apart. This is all designed tighter than I thought.

I saw the tuner alignment test point(labeled W). This is the grid leak circuit you mentioned. Why isn't this RF, instead of the passband response voltage shown? This point must be detected to get the response curve, no?

Steve

W is near the middle of the picture.

I guess nobody knows. I don't either. :tears:

I saw the tuner alignment test point(labeled W). This is the grid leak circuit you mentioned. Why isn't this RF, instead of the passband response voltage shown? This point must be detected to get the response curve, no?

W is near the middle of the picture.
It is detected, by the tube's grid/cathode performing the diode function.

I never heard of a cathode-to-grid diode action. If there is a diode action, then wouldn't the results be the video (plus some weird sound on the FM audio). Were would the IF frequency come from if the RF is detected?

Is the sweep input so strong that the tube is driven into Class C operation?

Where can I read about this circuit?

-Steve

I never heard of a cathode-to-grid diode action.

Google 'grid leak detection'. It's the classical AM detection method used in the earliest tube radios. It utilizes the natural diode action that occurs between a tube's filament (cathode) and grid ('anode') to rectify the amplitude-modulated carrier.

In the case under discussion here, the sweep generator's carrier, rectified and displayed on the scope, denotes the bandpass of the TV tuner.
If there is a diode action, then wouldn't the results be the video (plus some weird sound on the FM audio).
The two fixed-frequency markers or 'blips' on the trace are the sound and video carriers.
And yes, the TV would probably display some pretty weird stuff just from the genny's 60-hz sweep rate (though i never tried looking at it during an alignment).

Where would the IF frequency come from if the RF is detected?
The IF is not derived from detected RF.
It is the 'beat' or difference frequency between the local oscillator (LO) and the
incoming carrier.
Or in the case here, there are two IF strips. The first one is tuned to the difference frequency between the LO and the video carrier.
The second strip is tuned to the difference frequency between the LO and the sound carrier.
The video and sound carriers are 4.5 mhz apart.
Hence the two IF strips are tuned 4.5 mhz apart.

This system was superceded by the intercarrier method, in which the sound carrier is included in the video IF, and picked off right after the video detector at 4.5 mhz, amplified and detected. This simplified things and greatly reduced parts count

Hi 88,

I think I am getting this. With a capacitor in the grid circuit, the charge is held to a level depending upon the amplitude of the ac signal, charging only on the positive swings. So you get the envelop / detected waveform on the grid.

AND / BUT, the mixed radio frequencies still appear on the plate.

Horray! I got it. :thmbsp:

Thanks for your patience.

Steve

BOOYAH !!
:banana::thmbsp: