[Mondial]

Do you have the grid cap wire of the 75 routed inside its tube shield?

If the wire is outside the shield it will pick up the electrostatic field generated by the plate of the 42 output tube, producing positive feedback and oscillation.

I had this exact problem with my 60 until I rerouted the grid wire inside the shield.

[morzh]

Mondial

You are absolutely right. It was not. As soon as I put it inside, the oscillation stopped.

What is it about this particular radio that makes it so sensitive?
Proximity of 75 and 42? Not the first radio to have output tube near detector.

Well, thanks, this did it for tonight.


I also found an ungrounded cap 42, but it did not affect anything.

Resume:

1. complete loosening the band switch.
2. Possibly change the volume pot.
3. Align.


After Florida.

[morzh]

While listening to it, I decided to put in a short antenna wire.
At which point radio quit.

After short poking I replaced 6A7 and it wrked then.
Switched the tubes several times, yep - it quit. Just like that. I can hear buzz while touching grid cap or antena, but no stations.
Weird when a tube just does that.

[Eric Adams]

You're not alone, Mike. When I first got it I replaced the electrolytics and fired it up. With a 3 foot wire for an antenna (and a stuck band selector switch) I was able to pull in AM stations loud and clear. Now that the band switch is freed up I fired it up and all I get is static and the volume control has just one volume no matter how I move it!
I've decided to punish it by putting it on the shelf for a while.

[morzh]

Eric

It is possible you got some lubrication into where it does not belong, or a contact got bent.

Mike.

[Eric Adams]

I know. I'm just too PO'd to look at it right now

[morzh]

It is pay me now or pay me later. And as long as it is something you enjoy doing, might as well do it now.

[Eric Adams]

I know. It's just that being retired there aren't many things that bother me any more. So when I run into a problem with one of my radios, it upsets me more than it should.
That's OK. it's time for a diversion. I just got my latest Amazon delivery. I'm going to sit down now and read a book about Wernher Von Braun.

[morzh]

Eric

let me give you a bit of pep talk.

We restore radios because it gives us pleasure to restore them. In fact personally I specifically do not buy radios that are in fully restored or even working condition, I want to bring it back to life myself, and troubleshooting is a thing I enjoy and I think you should too!
So if it does not work, it gives you an opportunity to exercise your noodles and feel satisfaction when you solve the problem at hand.
Especially that other things do not bother you anymore.

"Snowflakes don't bother me, snowflakes don't bother me!" (Daffy Duck).

Think of what Werner Von Braun would say if you gave up!
(BTW he is phonetically "Vehr:nehr Foh:n Brahon", not "Werner Von Broh:n" as those who his V2 bombed pronounce it )

[Eric Adams]

I'm with you, Mike. I, too only buy radios that need work. Yes, to me the fun is getting something that doesn't work or look good and bringing it back to life. Years ago I was a master auto technician. I used to specialize in problem cars for the main reason that I got to use my head and I felt great when I found the problem.
The thing that gets me is that I had it working and it really was working great. Then I messed with the switch and now it looks like I created more problems. So, before I get really aggravated, I'll put it aside. After all, I still have the cabinet to complete. Then after a while I'll get back to it and get it working again.

Oh, by the way, the author of the book explains that his last name should be pronounced Von Brown

[Warren]

I agree, even though im just a begginer at repairing radios I feel it is all about making it look nice and work.. thats the fun. Not alot of fun to buying an old radio that works and just put it on the shelf... Although there are a fe wI might buy like that sometime, just to get them.

[morzh]

Eric

I would treat with suspicion an author who does not know how to pronounce his subject's name.

Von in German sounds like "Fon" as "V" letter in German is called "Fau" (fah-oo) and so was the name of his rocket, "V2", "Fau-2" for "Vergeltungswaffe" (Fehr-gel'-toongs-vahf-feh).

Alhough he is correct on Brown as it is in English sounds as Braun in German (and means the same too).



Anyway, good luck with the radio!

[Eliot Ness]

Sometimes setting something like that chassis aside for a while helps. I know when I'm troubleshooting at work, and I have a bad habit of not stopping until a system is fixed, that taking a break helps. On numerous occasions when I have forced myself to walk away and take a break in the cafeteria or coffee shop I'll suddenly get an idea while my mind isn't intensely focused.

[Eric Adams]

That's how it works for me, John. The good thing in my case is that I can walk away from a problem for weeks at a time. Which is what I'm doing on this one.

[morzh]

After standing for two weeks the band switch refroze again.

Sam actually gave me a can of PB Blaster.

I am trying it, so far with little to no effect.

Does anyone know where the best application point is?