[murf]

Hi guy's,
I would like to figure out why my Philco 42-1012 radio is not performing as it should.
It was re-capped about a year ago, and has never had the kind of volume that a 10 tube radio should put out.
When I got the chassis, it was a replacement for the original chassis that had a fried tranny.
Therefore, I don't know what condition the chassis was in as far it playing or not.
I just re-capped it and hoped for the best.
SInce getting it running again, it has never had good volume like it should.
If you crank it up to where it should be playing loud it just gets distorted without really getting loud.
I am thinking maybe bad resistors on the output tubes?
Or maybe low voltage from the tranny?
Not sure which of these tubes are for output?
Seems to pickup plenty of signals on all bands.
Any idea's from the Philco pro's?
Thanks

[codefox1]

Well, to split the diagnostics in half, can you run a signal from the volume control to a known good amplifier/speaker system (of course aware and prevent all shock hazards, and ask if not sure!) Also invest in a modern inexpensive digital meter to check voltages, etc. If you mis dial and blow it up, so what?

[morzh]

Murf

If you are methodical in your approach you will easily get to the root cause.

1. Was it ever playing well?
2. If yes, were the tubes OK?
3. Whatever it was, are they OK now?
4. Have you changed EVERY cap (OK, forget micas).
5. Have you checked EVERY resistor? No point guessing "could it be a bad resistor", just check them.
6. Yes, voltages. But, if your tubes are good and your resistors are good, and your wiring is good, your voltages will likely be good too.

Start with the basics, that will likely give you your answer.

[murf]

Has not played as it should since I first received this replacement chassis.
Condition unknown when I got it.
Owner said the tranny was good.
After I received it I re-capped it and replaced the tubes.
Re-checked tubes, except the xxl tube,which is not in my tube tester book.
Some of the resistors are a bear to get at and have short leads,which makes them hard to check.
Do you check them in place, or snip one end and test for a more accurate reading?
The volume switch was replaced some years back as well.
Could be a problem there?
The pushbutton power button went bad,so they replaced the power switch with a volume/power switch instead.
murf

[morzh]

Resistors oft cannot be checked in-circuit.

I usually see first if there is any DC path in parallel to a resistor, if not (it connects to some capacitors or to a tube's grid) then it is OK to check in-circuit, if there is - you have to use your judgement.

For example, say I have 10K resistor and there are some branches off of it where you see 250K or some 1M resistors creating DC path, it still can be checked, but if the resistors are comparable then they will shunt the resistor you are checking.

A good indication of a bad resistor, if the DC path is present and it is still above the nominal, it is clearly bad as if anything it should be lower.

An electrolytic cap in parallel or through small resistance may give you headache when checking a resistor as it will take time to charge and during that time your value will be all over the place if using DMM and the analog meter will show low slowly rising value.


But as bad as resistors are, the caps are the worst as almost no cap can be adequately checked by a C-meter in-circuit, the resistors will distort the heck out of it.

I try not to snip the resistors off but unwrap the lead with a hot iron, but this is a bit tedious.

In my experience (which mind you is not too extensive when it comes to old radios) with the 1940 and older type radios almost 100% of the carbon resistors (dog-bones) have to go, none of them is below 20 to 80% deviation, most being 50% up which is unacceptable though the radio may still play and that dupes folks into thinking the resistors are OK.

Wire-wounds on the other hand, unless open, do not age at all value-wise, as the wire does not go anywhere; all wire-wounds I saw are right where they are supposed to be. Those I replaced were opened, probably due to overheating.