Dumont RA-110 from ETF
 

Managed to get this set in the silent auction for $20 :)


The bad news: 19AP4 is toast

The good news: Cabinet has had a decent amateur refinish job and the knobs were sitting inside a coffee cup tucked between the picture tube and chassis.....but that's not all!

After giving the chassis a once over, I'm convinced this was a working set that had a picture tube failure. The recap job here is artistry. Whoever did this job used some funky 2 x 50 uF 500V UK manufactured caps and mounted them neatly in the chassis. Not really any info out there on them, they say FAC/RD37DUK 95-42.

They make everything look so neat, in the midst of what would be long terminal strips of caps mounted on the chassis if I were the one doing the job. Even the disc caps are all new.

Also, there's a funky relay underneath, with one wire labeled COIL. A quick glance shows that the wires go between the power transformer and the twin 5U4s. Could be some type of surge surpression that someone built in, like a soft start circuit?

Anyway, I'd love to shake the hand of the man who did this work.....

:thmbsp: I'm just about 99% positive that you will find that relay is a "field repair" replacement of a Dumont factory supplied item .

I'm less sure as to it's exact functioning , but my guess is that it was to protect the CRT from being phosphor burned in the event of a sweep failure ?

I don't have a schematic to be able to say. I just can't recall ever seeing anything like this in any set I've ever had my hands in.....

The relay was standard fare for Dumont/Crosley sets. 5000 ohm coil.
Usually bad and often just bypassed. 6AL5 activated. I recently replaced
two.

WIll it not wake up at all? On say 8-9 volts--will is give decent emission--or is it just "dead"?

The RA-110 manual is on our site.

Those are guitar amplifier filter caps... manufacture stopped around 2001 or so, but they were common in Marshall and other british made tube amps.

So, what is that tube mounted underneath the chassis?

That's the odd thing. Powered it up on my tester, 6.3V, and let it warm up for a minute. Walked away for a sec, heard a quiet SNAP, and the filament went dead :(

Never had that happen before.

Thanks Steve, I was actually reviewing the DuMont service notes and find it odd that they claim that the RA-110 and RA-103 chassis are basically the same, especially since the RA-110 has a separate HV chassis. But since I've never had my hands into an RA-103 before, I can't really say.

It's a 6AL5....

Sorry to hear, that is typical heater burn-out for a very gassy tube... likely the 19AP4 was pretty much "up to air" when you got it. How do the getters look?

jr

I have the same set in blonde. I picked mine up on Ebay for $10 and like yours had a dud crt. I picked up a tested like new crt for $75. The set was recapped in the recent past so I tried it and it works well except that it needs a new focus control. The winding of the control is burnt in the "sweet" spot so I cant get the raster as sharp as it could be.

crt
 

I have a crt if you decide to keep it.

Oh, I'm keeping it, believe me :D

Might have one lined up, but if not I'll definitely let you know :)

I didn't notice anything out of the ordinary or remarkable....they weren't white. But then again when I heard the SNAP and the filament went dead....well.....that was about that.

Set's still in the garage at the moment. I hafta take 3 doors and one long stairwell railing to get it in the house :)

i have one , started to recap the chassis and got side tracked on other sets , i hope to finish it soon and see what the end result is
the crt was very weak , i got one from another vk member and put it in , the original one i was going to put on the side in the hopes to rejuvenate or rebuild if there is ever a rebuild place again one day anyway the socket came loose and off and as i was carrying it it slipped , my thumb hit the glass nipple , a nice air in rush sound occurred and that was the end of that

The disc caps were originally paper capacitors. May not run as well. They are in critical circuits, and, may cause problems.
The solenoid powers on B+ when set is nearly warmed up so it won't surge as badly, which, surges can damage parts, and, Dumont knew that. By the way, Most early Crosleys were made by Dumont, or, RCA.
Bill Cahill

So I'm in the final stages of restoration now!

Okay, to be fair, it was mostly restored already. Anywho.....

I have one filter cap to do. It's a double 70 uF @ 175V. Weird thing is that there are no polarities marked on the cap, 4 wires, two of which go to ground.

I would normally assume the negative leads are chassis ground, and the positives go to wherever they go, because it's not labeled as a bias cap in the Sams. But, on the chassis ground side of the caps, it almost looks like a "+" scrawled into the solder. I've never seen a filter cap with NO polarity markings on it whatsoever, and 4 wires coming out of the cap, two on each end.

That said...what way does the replacement go in? :dunno:

If I am looking at the correct schematic (Sams 93-4, covers RA-103D/RA-104A/RA-110A), it shows that the positive leads of both 70-mfd caps (C9A and C9B) go to ground. The negative leads go on each side of a choke-resistor combination (L2 and R135).

Phil Nelson

Thanks for double checking me. It confused me because I was under the assumption that only bias caps have a positive ground, and these weren't labeled as bias caps. Right about here is where the gaps in my knowledge become chasms....

That's a weird looking electrolytic. I don't recall seeing one with a pair of leads at both ends like that.

Phil Nelson

Sure it's not on the yoke circuit? Or, just a weird bias?
The can likely isn't part of the electrical circuitry.
Trace your wires.
Bill Cahill

Splain.

Simple.. Electircally, the two capacitors are not connected to the can.
What colors are the wires? Where do they connect?
Bill Cahill

Connected to what can? The two capacitors ARE that yellow cap, one on each end believe it or not. Picture sawing it in half and each half being a stand alone filter cap. Weird as it is, that's what it seems to be.

The thing it's encased in is a U-channel that sticks up on the chassis and holds two 6X4 tubes horizontally. Super weird design for sure.

I've seen double ended, cardboard-sleeved filter caps before. 'Cept the leads coming out each end were red & black, clearly indicating polarity.
They were used in Sears 17" portables, in the doubler circuit with seleniums.
The first time I ever replaced one, I (mistakenly) thought the red lead coming out one end went with the black lead coming out the other end:eek:, and proceeded to wire it accordingly. The dang set came on and worked, but with humungous hum bars and hourglassing.
I quickly corrected the goof.

Here's a pic of the one end of the cap. I shouldn't say that it's *not* marked for polarity, because it clearly *is*, but it's not so clear. I had to take this picture 5 times and then enhance it to try to get it so that you could see. There's just a "+" carved in the solder, and it's so light that it's hard to tell it's even there. It's not even really visible on the other end of the cap. Other than the values stamped into the side of the cap, it's otherwise unmarked.

Second pic is the new caps installed where the old one was.

Next question.....
 

Chassis is in the cabinet and I'm just a 5V4 away from first power up. Ordered one up on ebay :)

Swapped the 19AP4 out of the Emerson I just got. I got a tip to lay the cabinet down on its face to install the tube, and that is dead on. Any other way risks breaking the picture tube.

The anode is securely on, but on the other side is this ground strap. Where on the chassis should this be making contact?

on my 109A set and another its position is down and the lower bend part or "J" should touch the chassis when you slide the chassis forward, it does not screw to the chassis but just touches it to ground, it looks like it is on backwards so you will need to flip it over and down

First power up. Not perfect, but it focuses in and has great sound. Inadequate width, not very bright, and the picture's not lined up, but it's something :)

Video: https://www.youtube.com/watch?v=Hk2S...ature=youtu.be

Weird how it's just rolled up on the left...

https://www.youtube.com/watch?v=OELi...ature=youtu.be

did you replace all of the paper caps yet?
there are a few in the Horiz Sweep area that when bad/leaking will cause this, and also a weak damper tube 5v4 would cause this, if the Horiz drive is turned up too high will cause this also
I would start first making sure all the caps in the Horiz osc/output/flyback are new, there is a resistor r122 and r120 that will change value, check those
But the Capacitors c101,102,103,106,105,107 is very important

All of the paper caps have been done. This set was totally restored when I got it, except for the one filter cap mentioned above. Even the disc caps are new...picture tube was just shot.

I agree, all signs kind of point to the damper circuit especially with the dim raster, but the 5V4 is new, just got it in from ebay (it was the only tube I didn't have). Tested strong before putting it in the set.

I've obviously got multiple issues here....it's got extreme foldover in the horizontal right in the middle of the screen and lacks width. Width control does nothing to improve it, so I'm inclined to think that I've got a bad horizontal output transformer. Gonna have to pull the chassis and ohm that out.

The horizontal drive was maxed out, but even bringing it all the way back to halfway caused no change, and with width also causing no change, that also points me to the horiz output transformer. Sound right?

I have a known good Flyback and Yoke from the 12Qp4 version of that set, but the 19" version has a beefier Flyback part numbers are different.
one of those chassis I had one of those Riveted Wirewound Resistors was bad, but I can't remember which exact one
of Course you know to be careful when measuring Pulsed Voltages around the Sweep area so you don't Damage your Meter

Well, one of those is for the focus coil, and the set does focus, so I can assume that's good. Other is a bleed resistor. Probably will end up having to check them anyway.

Unfortunately the only voltage test adapter I have is for a 7 pin miniature, so that's going to limit me in testing chassis voltages, and I'm sure as hell not doing it from underneath ;)

Maybe it's time to finally buy an octal one. Never really needed one up till now.

Having never seen horizontal roll up before, I went to the shelf and grabbed my trusty GE Tele-Clues binder. Well son of a gun.

Tossed the 5V4 on the tester, and it was perfect, so I got to thinking of what ELSE might cause the damper tube to be out of circuit. Peered underneath, and why HELLO Mr. Capacitor!!! Apparently something came loose from the previous tech that did the work! Yay! :D

Problem solved, right? Nope.

Clip leaded the cap across what I figured was a very obvious connection as seen in the pic. Powered it up and heard a SNAP. Shut it down. Grr.

The one end of the cap is definitely at pin 3 of the octal socket that goes to the HV chassis. It's a .1 uF. Have to do some tracing to figure out what the devil is going on.....

Definitely have the right attachment point according to the Sams. But, found a half dozen OTHER loose solder joints, some barely touching. I swear I gave the whole chassis the once over too, before installing it.

Welp, I have something to do tonight :)

I really like seeing yet another DuMont coming back to life. I love the way they were built.