Dumont RA113 "Burlingame" restoration

[bandersen]

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.

[IsthmusTV]

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

[dieseljeep]

Originally Posted by bandersen

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 ?

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

[bandersen]

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

[dieseljeep]

Originally Posted by bandersen

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.

[bandersen]

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

[earlyfilm]

Originally Posted by bandersen

. . . . 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.

[bandersen]

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


One of the 2.2 ohm filament resistors had cracked so I replaced them both.


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.

[IsthmusTV]

Originally Posted by bandersen

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.

[bandersen]

Originally Posted by IsthmusTV

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.

Originally Posted by IsthmusTV

...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.

[bandersen]

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

[bandersen]

I finished up work inside the HV box including a new 40kV anode lead.


United Electron 1X2 tubes. I don't think I've seen this brand before

[egrand]

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/sho...d.php?t=179305

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

[bandersen]

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

[bandersen]

I salvaged a nice anode cap from an Admiral then continued work under the chassis.


Better take a look inside this box.


Yep, two more paper caps and some resistors almost double the resistance they should be.