Philco 42-321 volume issue
 

I'm working on, or rather piecing together, about the worst condition radio that I've ever come across.

This radio was a friend's grandparents set, and has a huge amount of sentimental value. It must have bumped around a lot of attics and garages....the chassis was rusty, and all of the wiring inside was rubber, and was completely rotten.

I've rewired most of the set and recapped it. Miraculously, it actually sounds very good but the volume is about twice as loud as it should be....wherein lies my dilemma.

Normally, I'd go in and start testing resistors, but everything in this radio is so fragile that I dare not do this at random.

Can anyone help me with what to look at here?

Schematic: https://www.tubesandmore.com/schemat...on-corp/42-321

Normally too loud is not a problem as long as minimum pot setting is at the lower end of listenable. Is it hitting distortion?

It looks like an AA6 so no 'phunky philco phase inverter' to cause problems. If it is fragile check voltages against the print. You may want to look for other schematics for it with more voltage data. You ought to be able to check for resistors that have drifted high without desoldering or disturbing any, and if they are that brittle you may just want to replace them.

It hits distortion at about the middle of the control. Before that, it's just loud and proud.

Replacing resistors means maneuvering around other brittle wiring that goes up into the IF cans, which are riveted together internally (you can't just remove the shell and rewire them, or I would have). Not to mention wax coils that bubble up FAST when you hit the terminals with a soldering iron. I've got much of it rewired, but a lot of this wiring was done during assembly.....and difficult to get to *if* the radio had led a kinder life.

The whole idea here is like heart surgery on a 90 year old patient. As minimally invasive as possible.

If the resistance element in the vol control were open at the ground end, it would cause what you describe (or if the lug-to-ground connection were open).

'Ground' in this instance refers to the isolated or 'floating' common ground buss, standard in most all post-1940 series-string radios. Sets with power xfmrs continued to use chassis ground.

So let's work this the opposite way....

In this circuit, where would I be able to install a modification to cut the audio level by 50%?

I was able to test a few resistors in the set, which spec'd okay. When the Philco factory wires this sucker, they left zero lead length between the resistors and tie points. No way to test anything by taking it out of circuit. Which, fine, if I had to replace them, but as I said everything's too fragile in this set to even attempt it.

If it were my radio I'd search out a parts chassis....but that's part of the heritage the people want to try and preserve.

I'd say Coot is on the right track. The volume pot is probably the culprit. Solder in a few various resistors of say, 1000 to 100 ohms from the third lug of the pot to ground (pot's body) and see if that doesn't solve the problem.

Which would you classify as the third?

For the heck of it I would try this (assuming the control element is open at the bottom end)..

First verify solid continuity (zero ohms) from bottom lug of vol control to ground (the common ground buss, not chassis).

Using a couple of clip leads, try subbing a number of random value resistors, say 100 ohms to 100K ohms, between the middle lug of vol control, and the bottom (ground) lug. Sub them one at a time. You should be able to find some value that'll produce usable control action, though it'll be very nonlinear.

The set happens to be on the bench within arm's reach. That resistance box I rebuilt sure does come in handy!

Dialed it in and it's at the perfect volume with a 4.7K resistor. Thanks loads (again)!!! :)