Dumont RA-113 (B3) restorations

[bandersen]

The service info talks about the flyback being an efficient auto-transformer design that has tighter primary/secondary coupling and uses smaller wire gauge.

[bandersen]

I went to check voltage around the sync amp and quick realized I neglected to remove the shield and missed some caps :0


That are is the sync amp and separator so I've got my fingers crossed I found the problem. Going to recap right now and give it another power up.

[bandersen]

That can't be good


Found another cap hiding deep in the bowels. It's the coupling cap between the sync amp and sync clipper.


OK, that got the sync working, but now I have horrible bending and brightness bars. I figure there must be some major hum in the b+.


Yep, sure enough. I connected the 2nd main filter cap to ground when it should be the B- rail.

[Crist Rigott]

Very cool Bob.

[bandersen]

The tuner contacts seems a little dirty and might benefit from a little cleaning but I'm not sure how to get it open. I think I need to turn four little clasps on top, but it seems other stuff will prevent it from coming off. Even if I pull the three tubes and shields, it look like the coil will be in the way.

Am I missing something? Has anyone else opened up one of these while it was mounted in the chassis ?

[Phil Nelson]

I'm afraid you need to unsolder a few connections and pull the tuner. This article has some long bits about cleaning & lubricating an RA-113 tuner:

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

Start at, "Removing the Tuner."

Every inductuner that I've looked at had considerable petrified grease, etc., inside, so it's a good long-term strategy to clean & re-lube everything, even if the tuner turns at the moment.

Regards,

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

[bandersen]

OK, I was afraid you might say that Between your excellent, detailed writeup and the second chassis for reference I should be able to manage it.

[bandersen]

I managed to get it out without too much fuss. I'm going to try and keep the dial attached so I can avoid restringing.




I hope I can get it as clean as Phil's

[Radiotronman]

My Dumont RA-104's tuning still works, but is sluggish at some points. What did you use for lubricant?

[bandersen]

Nothing yet. I just started cleaning it. The Dumont service info recommends Lubriplate #105. Checkout pages 23-24.

http://www.earlytelevision.org/pdf/d...es_ra-111a.pdf

[bandersen]

There's a stiff steel wire wrapped around the horizontal hold control shaft that makes it hard to turn. The other chassis doesn't have it but I think I may have seen something like it in the past on other chassis.

I'm guessing it's there to ground the shaft or perhaps stiffen it up so the shaft doesn't move if the knob is accidentally bumped.

Anyone seen something like this before ?

[Electronic M]

Could also be a spring from elsewhere that a previous repair guy put there so as not to loose, and then forgot to reinstall where it belongs...

[Kevin Kuehn]

It appears to me that someone made it to hook over the top edge of that chassis. My guess is a tech did it to satisfy a customers request for a more tamper proof Horizontal Hold control.

[bandersen]

I just reviewed the service notes and see that the inner control is volume/power! How odd to combine one of the most used controls with one of the least used. I sure wouldn't want the hold control moving when I adjusted the volume!

[Radiotronman]

That is strange, probably why that spring is there, because the on/off volume does move that control some. I've never seen that combination before.