Dumont RA113 "Burlingame" restoration

[bandersen]

I finished replacing the leaky mica caps and out of tolerance resistors including the one in the eye tube base then redid the audio alignment. Bingo!

The eye tube now responds like it should, I only get good sound at one distinct point on the dial per station and it coincides with a sharp picture.

Time to start putting this set back together

[IsthmusTV]

Good show, Bob! Congratulations. After spending more time tuning around with mine, I notice that I also have the double peak issue with the audio. It's not as pronounced as yours was, but clearly I still have some work to do. I'll start by looking at those mica caps.

Are you going to do anything to the cabinet? I haven't done anything to mine except superficial cleaning.

Again, congratulations. Your friend should be very pleased.

-Clark

[Kevin Kuehn]

Congratulations is right. I still don't understand how those bad components would cause the reveres action you were getting on the eye tube. Suppose it was a combination of the leaky caps which caused a false alignment indication at multiple resonances. Was the alignment off a lot when you went back through it? At any rate I think we're about to the point in time that we need to start shotgunning all mica caps. Although sometimes those types of caps make for a excellent learning experience.

[bigaudioal]

Congrats, Bob! I just watched your YouTube video last night on this set. Nice to see that you solved the audio issues and the tuning eye reverse issue. Cannot wait to see the next video of this set functioning!

[Phil Nelson]

Originally Posted by Kevin Kuehn

we're about to the point in time that we need to start shotgunning all mica caps.

Micas can go bad and I have replaced my share of them, but many more in sweep circuits (horizontal, vertical) and HV circuits. Audio circuits tend to be more forgiving, but if you find a bad one -- or two -- there, of course it has to go.

I would not advocate shotgunning micas in IF stages unless you are well equipped and well versed in alignment, since a slight change in lead dress may kick things out of whack. Ditto, even more so, for the tuner section. Service manuals often included warnings to keep your clumsy mitts out of the tuner.

These days I look on mica caps as I do resistors. Generally more reliable than the hopeless paper caps, but not immortal. If a basic (paper + electrolytic) recap doesn't magically fix everything, then the next phase is to look at micas + resistors. One thing that I do during the basic recapping phase is test every component on the same terminal where I am connecting a new cap, the theory being that if I'm disturbing (unsoldering & resoldering) anything on that terminal, I may as well deal with everything at once to avoid trashing the connection with repeated monkey-wrenching. That way, I naturally uncover some other bad parts as I go, although it's not very systematic.

Phil Nelson

[bandersen]

Originally Posted by IsthmusTV

... Are you going to do anything to the cabinet? I haven't done anything to mine except superficial cleaning.

Again, congratulations. Your friend should be very pleased.

-Clark

Pleased and relieved as I really want to get back to my other projects

I'm not going to touch the cabinet but the owner asked for suggestions on preserving the finish. I'm no expert on blonde finishes but I figure a quality, non-silicone furniture polish found be fine.

Originally Posted by Kevin Kuehn

Congratulations is right. I still don't understand how those bad components would cause the reveres action you were getting on the eye tube. Suppose it was a combination of the leaky caps which caused a false alignment indication at multiple resonances. Was the alignment off a lot when you went back through it? At any rate I think we're about to the point in time that we need to start shotgunning all mica caps. Although sometimes those types of caps make for a excellent leaning experience.

Yes, the IF between the 1st & 2nd audio stages was off as was the discriminator. Those are the areas where I replaced three micas and several resistors.

I would call it a reverse action - more like the bias point was shifted over so that the left bar would never dip below the reference bar. Now, it swings to either side. I'll show that in detail in the next video up later today.

Originally Posted by bigaudioal

Congrats, Bob! I just watched your YouTube video last night on this set. Nice to see that you solved the audio issues and the tuning eye reverse issue. Cannot wait to see the next video of this set functioning!

That video was my first attempt at alignment. I'll post another video later today showing the replaced micas and second alignment with the correct tuning eye action and sound.

Originally Posted by Phil Nelson

Micas can go bad and I have replaced my share of them, but many more in sweep circuits (horizontal, vertical) and HV circuits. Audio circuits tend to be more forgiving, but if you find a bad one -- or two -- there, of course it has to go.

I would not advocate shotgunning micas in IF stages...

I agree and didn't touch the tuner. Also the micas in the video IF tested OK so I left them alone. It was tempting to replace them all, but that would require yet another alignment plus those micas get expensive! Also, there's always that risk of slipping with the soldering iron and damaging a coil or other fragile component.

I think the big culprits were the bad 10pF coupling mica cap between the 1st and 2nd audio IF stages and the two bad 1K resistors which threw the bias off the 2nd tube.

[robert1]

Originally Posted by bandersen

I finished replacing the leaky mica caps and out of tolerance resistors including the one in the eye tube base then redid the audio alignment. Bingo!

The eye tube now responds like it should, I only get good sound at one distinct point on the dial per station and it coincides with a sharp picture.

Time to start putting this set back together

As i mentioned sometime back on your You-Tube video, Bob, i learned a long time ago to just go ahead & replace all them postage stamp (Mica) capacitors because they can & will fail. after many years of lack of use, moisture & humidity can get inside of them & contaminate the Silver Oxide (or whatever electrolytic material) they use for a dialectric. it amounts to the same thing as Silver Oxide Migration that is common to I.F. cans. back then, the technology just was not there to manufacture a perfectly sealed capacitor. those Micamold capacitors were not really much better then paper capacitors, especially in Humid envirements.