DuMont RA-103 Doghouse lives . . . kinda.

[bigaudioal]

Well after a bit of work here and there over the last few months I finally powered up the Doghouse. I replaced all the electrolytics, all bypass caps (except for micas and about a dozen small, little ceramic pf caps. Also replaced all resistors higher than 1 watt.

Slowly powered up on a variac and got a raster, messed up picture and good sound. Good first power up result for my third project. After tweaking I was able to get a picture that looks ok at the very top and then is severely stretched at the middle and bottom. So I went through the vertical and replaced ALL resistors and any small ceramic pf caps. Well, no change. Below photos show what I have.

Note - I am using a 12KP4 CRT (no ion trap needed) instead of the original 12JP4. Not sure this would be causing any of these these conditions? The picture will not fill out on the right side in addition to the obvious vertical issues. I have the yoke as far forward against the bell of the CRT as it can go. If I slide it back, the picture shrinks away from the top right side. Almost like if the yoke could come farther FWD it would fill out.

I will continue testing and replacing resistors and those small ceramic pf caps, but was hoping to see *some* change after doing this in the vertical circuit and saw no change.

I am going to ohm out the VOT and if that checks out, maybe pull the yoke and test resistors in there/replace any caps.

Any ideas??? Do I appear to be on the right track (VOT and yoke)? Only my third set working on it all by myself - so my diagnostic skills based on what I am seeing are not great yet. Set runs solid (well over an hour combined last night), even with the picture like this. Sound is great and all controls seem to function.

The GEICO GECKO sure looks funny this way. More like a velociraptor in the second photo!!!!

[bandersen]

The CRT shouldn't be an issue. All the 12" round B&W CRTs are basically interchangeable and they mostly differ in neck length.

Do you have a scope ? Could be the vertical oscillator is producing a distorted sawtooth waveform.

I'd also double check the vertical output tube, cathode bypass cap and linearity control.

[Tom Albrecht]

The vertical output transformer and yoke are certainly worth a careful look. I'd also double check the values and wiring of any capacitors you replaced in the vertical section. Also note that the vertical centering coarse adjust switch on these sets often has very dirty contacts, so check to make sure that isn't causing a problem.

Did you replace the big Candohm resistors? They have a high failure rate in this chassis. Since you mentioned replacing all large dissipation resistors, I presume you did.

And almost certainly I imagine you have swapped out the vertical tubes.

Can you check all the voltages on the tube pins in the vertical section and see if there are any significant deviations from the service data?

[bigaudioal]

Thanks for the suggestions. Glad I am learning enough to recognize what sections to concentrate on and my inclinations to concentrate on the vertical circuitry, VOT and yoke were good.

Bob, I do not have a scope yet, so flying blind when it comes to wave forms.

Tom, I have replaced all the candohms and resistors over 1 watt in the set. All caps are done (minus micas and some ceramic pf caps). All resistors and ceramic pf caps in vertical are replaced now too. I did try various tube swapping for the vertical section with no change.

I will proceed to test voltages on the vertical tubes, check wiring and controls, then ohm out the VOT and see where that gets me.

One thing that you did mention Tom, is that vertical switch on the back. It does function and adjusts the top part of the picture from WAY OFF the top edge of the CRT in one position, then moves the top part of the picture down in the other position. Which is the position I took the photos in. The overall poor vertical appearance does not change in either switch position however. I will try cleaning that switch too.

This is where the fun begins!!! Trying to track down what is off with my limited experience and knowledge. Thanks again for the nudges in the right directions.

[John Marinello]

I think it's a sawtooth issue as well, but make sure height + linearity adjustments are OK first, as those way off can produce a similar effect.

[bigaudioal]

Ok, so here is the loaded question.

If everything else checks out and tube swapping, caps/resistor checking, etc. fail to change the condition and we are looking at a possible sawtooth waveform issue - where do I go from there? That waveform comes from vertical osc tube, correct? So either the voltages are fine on that tube and the issue is with the tube itself, or the voltages are off and I have to track down where the problem lies feeding that tube, right? So test voltages back from tube to tube in vertical before osc tube until I get to a point where they are correct. Then my issue lies between osc and where they test fine.

This is all assuming that controls/caps/resistors, etc are all done and good. Just wanting to make sure I have the concept down really for diagnosing.

[Boobtubeman]

The Gecko looks like an ostrich in the first pic

SR

[bigaudioal]

Well two rookie mistakes fixed, and the set is rocking!!!

Found two caps that I replaced with incorrect values in the vertical. Put a .047 where there should have been a .0047 and put a .01 where there should have been a .1. Both in the R&C network between the vertical buffer tube and the vertical output transformer. That did it!!!! Plus a little focus coil adjustment to get rid of the neck shadow.

http://youtu.be/k4Un0oL1R6Q

Thanks to everyone that commented. Gonna miss the strange Gecko.

[Kevin Kuehn]

Very nice! The 12KP4 looks pretty good in there.

[bigaudioal]

Sure does. Thx!!! Just needed to adjust the focus coil a bit to get rid of the CRT neck shadow after switching to a crt with no ion trap.

Played great for over two hours. Power transformer was warm after that. I could keep my hand on it, so was not hot, but definitely warm. Warmer on the side next to the 5U4 and cooler on the back, but warm on the top too.

[tvdude1]

Just sent you message. Your dials and both gears are ready to go for your tuner.

[bigaudioal]

Thx. Shot you payment. Really appreciate it.

[bigaudioal]

Getting there. Of course will need to readjust when back in cabinet. Going to watch outside the cabinet for now . . .

[bigaudioal]

All resistors that tested bad are replaced. Calling this electronic restoration of the DuMont RA-103 DONE! Next steps - replace dials when parts arrive, finish cabinet restore and reassemble.

[tvdude1]

Did your dials show up yet? Sent them USPS.