1950s or '60s vintage Zenith TVs, Need some info

[Kevin Kuehn]

Originally Posted by vortalexfan

I have a signal generator but not an audio generator, would a signal generator work the same way?

Don't get hung up on the name. Take a look at the frequency ranges covered. If you can dial it down to an audible frequency you should be good. Typically 400-1k hz are used when chasing an audio signal through a circuit, but in theory any frequency the circuit can pass could be used, within your hearing range of course, unless your looking with scope.

[vortalexfan]

Update: Pin 5 of the 5AQ5 tube which is supposed to have 215V on it is only measuring 25V and pin 6 of the 5AQ5 tube is supposed to be 230V is only measuring 25V as well (same as pin 5), and pin 2 which is supposed to be 17V is measuring less than a volt.

[vortalexfan]

Originally Posted by Kevin Kuehn

Don't get hung up on the name. Take a look at the frequency ranges covered. If you can dial it down to an audible frequency you should be good. Typically 400-1k hz are used when chasing an audio signal through a circuit, but in theory any frequency the circuit can pass could be used, within your hearing range of course, unless your looking with scope.

OK, thanks.

[Kevin Kuehn]

How does your 245 volt B+ source measure where it feeds the 470(R56) ohm resistor?

If you have not replaced electrolytic caps C3B, C3C and one or both are very leaky it would certainly have that affect of drawing lots of current, pulling down voltages and cooking the 470 ohm resistor feeding that audio circuit. C51 being leaky could cause low audio, however it alone should not pull your voltages on the 5AQ5 down that low. It's highly suspect that one of the above electrolytic caps has either not been replaced or has become shorted(possibly installed reverse polarity). Certainly you've tested the 5AQ5 for shorts.

[vortalexfan]

Originally Posted by Kevin Kuehn

How does your 245 volt B+ source measure where it feeds the 470(R56) ohm resistor?

If you have not replaced electrolytic caps C3B, C3C and one or both are very leaky it would certainly have that affect of drawing lots of current, pulling down voltages and cooking the 470 ohm resistor feeding that audio circuit. C51 being leaky could cause low audio, however it alone should not pull your voltages on the 5AQ5 down that low. It's highly suspect that one of the above electrolytic caps has either not been replaced or has become shorted(possibly installed reverse polarity). Certainly you've tested the 5AQ5 for shorts.

I have replaced all 3 caps for C3 with brand new caps and I made sure to observe proper polarity, as for the 245V supply to R56 its only measuring about 220V for some reason.

As for the 5AQ5 tube, I've tried subbing in a known good 6AQ5 tube (as I don't have any 5AQ5 tubes, and plus I know on series string sets you can get away with upping the the tube voltage a little bit because of higher line voltages) and I get the same results.

[Kevin Kuehn]

Originally Posted by vortalexfan

I have replaced all 3 caps for C3 with brand new caps and I made sure to observe proper polarity, as for the 245V supply to R56 its only measuring about 220V for some reason.

So lets see now.

You said you have 220 volts on the right side of R56 and 25 volts on the left side(pins 5-6 of the 5AQ5).

That's 195 volts being dropped across your 470 ohm resistor.

195 volts divided by 470 ohms = 415 ma or nearly a half amp trying to pass though R56, a measly half watt resistor.

You have nearly a dead short to ground on the left side of R56. There is only 3 paths that current can be flowing from that point to ground, and only 2 which I can foresee that much current could be flowing, and honestly only one unless your 5AQ5 is glowing cherry red.

I seriously suggest you double check your newly installed capacitors, even if they do appear correct they may have failed. First off simply lift one leg of C3-B and see if your B+ comes up.

Edit - there is also the very unlikely possibility that your output transformers primary winding is shorting to ground, which you could verify by checking resistance from it's red B+ lead to it's mounting frame.

[vortalexfan]

...

[Kevin Kuehn]

Originally Posted by vortalexfan

...

No. You have B+ on the input to the 470 ohm feeding the audio circuit and very little voltage on the opposite load side. You simply need to follow the excess current path, which is indicated by your low voltage measurements. And please stop editing posts after someone responds to your questions.

[vortalexfan]

Originally Posted by Kevin Kuehn

No. You have B+ on the input to the 470 ohm feeding the audio circuit and very little voltage on the opposite load side. You simply need to follow the excess current path, which is indicated by your low voltage measurements. And please stop editing posts after someone responds to your questions.

Ok, sorry. Anyways, I think I figured out the problem this time... I checked C3B like you asked and sure enough my ESR meter measured that cap as being 77 MFD with an ESR reading of .15k ohms and it was a 10 MFD 350V capacitor...

[Kevin Kuehn]

Originally Posted by vortalexfan

Ok, sorry. Anyways, I think I figured out the problem this time... I checked C3B like you asked and sure enough my ESR meter measured that cap as being 77 MFD with an ESR reading of .15k ohms and it was a 10 MFD 350V capacitor...

Your ESR meter isn't of much use in this situation. Did you lift one lead and see if your B+ rises?

[vortalexfan]

Originally Posted by Kevin Kuehn

Your ESR meter isn't of much use in this situation. Did you lift one lead and see if your B+ rises?

No I haven't yet, I'll do it when I get up, I'm going to bed because I'm getting tired.

Should I lift the negative or the positive side of the capacitor?

[Kevin Kuehn]

Originally Posted by vortalexfan

No I haven't yet, I'll do it when I get up, I'm going to bed because I'm getting tired.

Should I lift the negative or the positive side of the capacitor?

Depends on if your an optimist or pessimist.

[vortalexfan]

OK so, R54 which is a 390k Ohm 1/2W 10% resistor is measuring 470k Ohms which is way out of tolerance would that cause some issues in the circuit?

[Kevin Kuehn]

Originally Posted by vortalexfan

OK so, R54 which is a 390k Ohm 1/2W 10% resistor is measuring 470k Ohms which is way out of tolerance would that cause some issues in the circuit?

You'd get a little lower plate voltage on V7, but that surly has nothing to do with your high current draw situation. Am I safe in assuming R56 gets blistering hot whenever you power the set on? Have you disconnected one end of C3-B?

[vortalexfan]

Originally Posted by Kevin Kuehn

You'd get a little lower plate voltage on V7, but that surly has nothing to do with your high current draw situation. Am I safe in assuming R56 gets blistering hot whenever you power the set on? Have you disconnected one end of C3-B?

I have but that capacitor has R54 and R56 attached across the positive side of C3B and so disconnecting the positive side of C3B from the circuit just leaves R54 and R56 tied together which would most certainly cause some issues in the TV.