So I've replaced just about every capacitor possible on this set, even some that were a little over kill from a previous repair and I wanted to check my work. The set is doing the same thing as before, but the hum is a lot more faint this time. Where do I need to look? The guy that gave me the set said it was working, then it quit on him so he put it away and quit using it.
So you go and start checking voltages, coil continuities and such.
the voltages Mike is referring to can be found on the
schematic.
I checked transformers and chokes, and those seem to be okay, no opens, and nothing ready in mega ohms, I'll have to check my Perpetual manual to see if it lists the voltages. Where specifically should I start?
By transformers do you also mean the RF transformers, oscillator coils, etc?
Have you checked the tubes?
"Nothing really in megaohms" when said of transformers has as much info as if you didn't say anything. Same goes for "The set is doing the same thing as before". How do we know what it was doing before?
In fact so far you have not done much to investigate and have not said much at all.
You have to start speaking in more precise language, otherwise you make us trying to guess things.
Start with voltages, measure coils, test the tubes, then tell us eactly what you measured.
I'll start with the 2 basics filter choke reads at 168 ohms, the output transformer primary is at 410 ohms, and secondary is at 245 ohms with half the reading at the center tap.
click on the link in post#3...the schematic has the voltages listed in the table.
Just checked some of the voltages on the tubes I can get to, they're reading what they're supposed to or close to it, the amplifier portion checks out as I am getting noise there, also did some of the basic tests to check the amplifier, the radio part seems to be where the problem is.
OK, can you pass the signal from generator starting from any point in the RF? (the one you referred to as radio part).
Anything, IF frequency is the best.
And the "noise in the amplifier" - does that mean that when you touch the control grid of 42 driver (pin 4 at the link below) it hums?
http://www.radiomuseum.org/tubes/tube_42.html
Well I finished replacing the rest of the caps and that got rid of one problem I was having but still no radio. There's 3 type 42 tubes in this radio and they all do about the same thing when you start probing around. I'm fearing this one may be above my knowledge if it happens to be a coil, but they all show continuity. I have to do this with a meter only, I don't have a signal generator.
Working with the meter only is tough. Especially if you have little experience doing this sort of things.
You could possibly buy a known good tube of each kind you have and try to sub one at a time.
Do you have any friends maybe who have a tube tester?
Any swapmeets happening around where you are?
Meantime, since you have a meter, why don't you measure voltages on each tube? This might give us some info.
I live in rural southeast Idaho, there was a business at one time that had a tube tester, but they closed a few years ago. There may be a couple collectors around that may have a tube tester. Would a bad tube cause the problem I am having? I have a couple ends to tie up still, but I'll have to see what I can figure out there.
Well....no reception....some audio....yep, a bad tube can cause it. So can other things.
But the good practice is, start with ALL known good parts, and you save yourself TONS of time, literally.
Tubes as easily removable and replaceable parts to me should be checked prior to the final check 100%. I NEVER will insert an unknown condition tube in a radio. At best it won't work, at worst.....it can blow your power, fry your resistor.....
So here's an update with some numbers, the 2 42's that are together have voltages at: 310, 312, -027, & 0. The 42 by itself: 232, 232, -011, 0. R.F. 78: 233, 0, 0, 5. 6A7: 234, 9.2, 4.5, 0, 0, 39.5, 46.8. The 37 I get zero voltage except for the filiment. The I.F. 78: 3.6, 110.4, 230. The 77 I can only reach on pin at 55.8 volts.
Hi Jr,
Voltages look pretty good. Take a look at pin 5 of the 6A7 to the chassis. Should see some negative voltage there (a few volts) if the oscillator is running. The 37 tube your not going to see much any voltage as it is acting as a diode detector.
Terry