The Family DuMont

[CaryLee]

Originally Posted by earlyfilm

Cary, I believe you said this is your first TV, correct?

I also understand that you have neither substitute tubes, nor a tube checker, correct?

Next step is to dim your lights and verify that the plates on the 5U4 rectifier, the 6BG6 Horizontal Output, and the 6W4 Damper are not getting pink as this indicates something is badly wrong.

If any plates are glowing, turn the set off immediately.

Since you have not replaced any resistors, I assume that a resistance check will not be productive at the moment.

I cannot call the Sam's part numbers as the only schematic of the RA-112 is the Riders one at ETF which uses the factory numbers.

http://www.earlytelevision.org/tv_sc..._diagrams.html

However, I'm going to suggest that you measure all the resistance reading listed in Sam's from tube sockets, with the set unplugged. This will give practice for the next step and it might spot a pre-existing problem.

Make a Xerox of the two pages of Sam's and write down the resistance, at each point and color marking the ones that are off by more than 20%.

If no tube plates were getting too hot, your next step is to check the voltages that are shown in Sam's voltage chart.

Follow the same procedure of writing them down, again marking those 20% off in a different color.

James

Howdy James!

Yes, this is my first set. I've done a couple tube radios, and a wind up phono (completely different tech!) The reason I've got this DuMont is because it's a family heirloom. I've run into some pretty good luck with it so far.It's nice to know it's history, and it's been in my possession for over 25 years, and I've been pretty protective of it.

As it started getting darker outside, I was able to look at the tubes as you suggested. No pink plates, so that was good. The darkness is also what led me to noticing that the CRT was apparently "coming back to life". I could see some VERY faint flickering, and started moving the ion trap around, and was able to brighten up the CRT immensely. I was pretty encouraged by that. Now I just have to figure out how to introduce a a signal so I have something to actually see.

We actually still have at least one UHF analog station broadcasting here..but alas, this DuMont has no UHF!

Thank you for the "system" for checking the resistors. I figure There's going to be some that need replacing. There's a LOT of them in there!

I do not have a tube checker. I've met a couple people who say they have one "somewhere", and say I can use it when they find it, but no one has dug one up yet. I'm starting to get enough tube driven stuff around here that buying a checker might be worthwhile. I do have a few extra tubes now. TV tubes are remarkably cheap, so buying them in lots is almost as cheap as buying one. I've got a couple 6J6's, 6BA6's, and several spare 6AU6's.

[CaryLee]

Originally Posted by bandersen

Yes, you will get FM reception in both FM and TV positions and the CRT filament is lit at all times.
The only thing that happens in FM mode is that the CRT brightness is cut off. All the TV circuits are still running including the high voltage.
So you really are wearing out the TV tubes and CRT while just listening to the radio.

Thanks! Now I understand how it works, and now that the CRT is lit up, I see it's working just as you describe.

Now I'm no engineer, but "I am a thinker"..and it sure seems DuMont could have come up with a better setup than to have to power the entire TV, and wear out ALL the tubes (including CRT!) just to listen to the radio!

I've read of folks putting a circuit into their old radios with "eye tubes" that shuts off the eye tube a few seconds after tuning stops. I guess certain German radios did this right from the factory. With radio "eye tubes" getting scarce and expensive, I've thought about it for my '38 RCA console. I've read that useful life of a radio "eye tube", 6U5, 6E5, and the like, is around 1000 hours. Not very long if you listen to the radio a lot!

Just dreaming out loud here (figuratively speaking..errr...typing), but I wonder how hard it would be to unobtrusively install some sort of cutoff that kills the TV circuit..particularly CRT, when listening to the radio. TV tubes, in general, are plentiful and cheap..but CRT's sure aint!

[Phil Nelson]

It's always exciting to see that first light on the screen.

You may be close to having a coherent picture. What are you using as a source -- VHS player, DVD player, etc.?

As you may know, wherever your TV has two tubes of the same type (say, two 6AU6), you can swap them and see what happens. If no change, then chances are that they're either both bad or both good. In restoring dozens of radios and TVs, I've found that the majority of old tubes found in those sets were still good, so the odds are somewhat in your favor.

You can also perform a simple dud/not-dud test on a tube's filament with an ohmmeter as described at http://antiqueradio.org/FirstStepsInRestoration.htm .

I would not go nuts replacing marginal resistors at this stage. If one is WAY off or totally failed, then replace it, but consider that many parts of your TV are working "purty good" if you're seeing a lit screen. Going overboard with mass replacements creates more opportunities for mistakes. As earlyfilm noted, it's worthwhile to do the systematic tests and record the results in any case.

At this stage, I would focus on getting an image on the screen along with audio. Then you can do selective troubleshooting.

Good progress so far!

Phil Nelson

[CaryLee]

Originally Posted by Phil Nelson

It's always exciting to see that first light on the screen.

You may be close to having a coherent picture. What are you using as a source -- VHS player, DVD player, etc.?

As you may know, wherever your TV has two tubes of the same type (say, two 6AU6), you can swap them and see what happens. If no change, then chances are that they're either both bad or both good. In restoring dozens of radios and TVs, I've found that the majority of old tubes found in those sets were still good, so the odds are somewhat in your favor.

You can also perform a simple dud/not-dud test on a tube's filament with an ohmmeter as described at http://antiqueradio.org/FirstStepsInRestoration.htm .

I would not go nuts replacing marginal resistors at this stage. If one is WAY off or totally failed, then replace it, but consider that many parts of your TV are working "purty good" if you're seeing a lit screen. Going overboard with mass replacements creates more opportunities for mistakes. As earlyfilm noted, it's worthwhile to do the systematic tests and record the results in any case.

At this stage, I would focus on getting an image on the screen along with audio. Then you can do selective troubleshooting.

Good progress so far!

Phil Nelson

Howdy Phil!

Thank you for the words of encouragement! My one big, huge, overwhelming "if" was the CRT. I had no idea what it was going to do. Family legend said it was a "bad picture tube" that retired the set, but after I learned something about how vintage TV's work, the symptoms didn't fit. I had hope that something else was bad..now it's looking like it was a bad power switch all along. Still, the only positive test I could perform was your suggestion of checking the filament, and it did test good.

I'm not sure what to use for signal source.."earlyfilm" mentioned a slight voltage travels through the chassis on this set that could travel the lead and damage a transistor device...might it damage a VCR or DVD player?

Any suggestions?

[Phil Nelson]

If your VHS or DVD player has an output in the back marked "To TV" or "RF," you can connect that to the TV's antenna terminal through a coaxial cable.

If the player has A/V output (1 video plus 2 audio for stereo), then you can connect those to an RF modulator like this:

http://www.radioshack.com/product/in...95#tabsetBasic

You would then connect the RF modulator's output to the TV's antenna terminals, again using a coaxial cable.

This is how TV collectors watch recorded material on their TVs nowadays, since the USA discontinued analog TV broadcasts several years ago.

You can buy that kind of RF modulator other places; I only gave a Radio Shack link because their stores are found in many cities.

Earlyfilm was talking about a different connector on the TV -- the phonograph input jack. That was designed to use an old-school input. Modern solid-state devices (iPod, you name it) are not designed for that use and might be damaged if you plug them in directly.

It's possible your CRT is weak, but in the photo it is lighting up enough to see, so it should work well enough to get you through the restoration, at least. Perhaps when you're done it will be good enough to watch. The CRT used in these sets is not super-rare, so if you decide you need a better one, you should be able to find one eventually.

Phil Nelson

[earlyfilm]

Cary,

First congratulations on getting one of the more complicated vintage TV sets, or I should say "systems," lighting up! These early Du Mont's are not what we call starter sets!

That set must have had years of dry storage storage! Usually one can hear the HV crackling up for the first time, but I forgot that you were from the driest area of the US.

Originally Posted by CaryLee

I'm not sure what to use for signal source.."earlyfilm" mentioned a slight voltage travels through the chassis on this set that could travel the lead and damage a transistor device...might it damage a VCR or DVD player?

Sorry I confused you. I was talking about modern AUDIO devices. Many of these are not protected against for this issue. Anything that is supposed to go through an antenna or video feed should be OK. Also, older tube era phonographs should be OK.

I'd try a your cable box if you have cable and it has an RF (channel three or four) analog output. If not, find one of the used set top boxes used to convert digital over-the-air programs in the early days of digital, that will be better. The most common problem with both of these is their output is slightly stronger than old high performance fringe area sets like your DuMont is expecting and that may cause sound buzz or picture bending, or even the picture flipping to negative.

The first thing to remember about a tube checker is that it also has to be recapped and then possibly recalibrated, since the same parts in them age just as a TV does.

Also you need to try to see if the focus control is just dirty or if it has failed. You have pretty high voltage there, so after cleaning, be sure to let the control completely dry before powering up the set, or you could fry it. This control is center fed from the raw B+ and helps provide both the 300v and 200v sources.

James

[David Roper]

Originally Posted by bandersen

The only thing that happens in FM mode is that the CRT brightness is cut off. All the TV circuits are still running including the high voltage.
.

Not so, not with a Du Mont anyway. Sets that did no more than blank the raster with an external phono input are really nothing more than a gimmick.


Any design that was done at all seriously will cut the voltage to the sweep section when in a non-TV mode and the Du Mont sets do this.

ETA: Well damn. I just checked the RA-113 skiz and can see there came a time when the Du Mont engineers stopped being serious! Even my '51 Emerson combo kills the sweeps in phono mode...and it ain't no Du Mont....

[bandersen]

Yeah, I was quite surprised to discover that while restoring an RA-113. I have a GE-802 with a beefy switch that cuts juice to most of the set while not in TV mode.

[old_coot88]

Cary,
Congrads on the successful power up. There is one paper cap i'd heartily recommend replacing as the first order of business. That's the coupling cap going to the control grid (G1) of the HO tube. The slightest leakage in this cap will cause the tube to overconduct, shortening its longevity.
If the tube is 6BG6, G1 is pin 5.



OOPs! Senior moment. Looks like you've already done a recapping. Presumably you got that one already.

[M3-SRT8]

Hi Cary,

I just 'tuned in' to this thread. Congratulations on resurrecting the Dumont. Not an easy first project.

I have a soft spot for DuMonts, obviously...

[CaryLee]

Turns out the rheostat that controls the focus is toast. About a third of the wire winds are eaten through.

I did hook up an old VCR/DVD combo with a built in RF output and was able to get a blurry picture..so that's good news.

Any hints on where I can find a 1200 OHM 25 watt ceramic rheostat with a long shaft? The Clarostat part number is RTV-220.

Photo soon...

[CaryLee]

Originally Posted by M3-SRT8

Hi Cary,

I just 'tuned in' to this thread. Congratulations on resurrecting the Dumont. Not an easy first project.

I have a soft spot for DuMonts, obviously...

Nice stuff! I hope to get as good a picture out of mine eventually. I just determined my focus control rheostat is a goner..

[CaryLee]

The SAMS calls for a 1200 ohm 25 watt rheostat...

Surplus Sales has a 1000 ohm 25 watt, left side of the page on link below..for $8..would that be close enough?

http://www.surplussales.com/Potentio...sRheost-4.html

[M3-SRT8]

Originally Posted by CaryLee

Turns out the rheostat that controls the focus is toast. About a third of the wire winds are eaten through.

I did hook up an old VCR/DVD combo with a built in RF output and was able to get a blurry picture..so that's good news.

Any hints on where I can find a 1200 OHM 25 watt ceramic rheostat with a long shaft? The Clarostat part number is RTV-220.

Photo soon...

Yup. Surplus Sales of Nebraska.

There's a 1k 25w and a 1.5k ?w on this page:

http://www.surplussales.com/Potentio...sRheost-4.html

Focus Controls are a soft spot on these old DuMonts.

[M3-SRT8]

Ooops. See you've already caught the SS of N page.

I bought a bunch of those a couple of years ago to keep in stock.

You can hang a 25ww resistor off the end of the 1k Control to gain a little more range, if need be.