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

[Kevin Kuehn]

Originally Posted by vortalexfan

Yes 10,000 pF is the same as .01 MFD but I'm not sure what the voltage is as it's not specified in the Sam's, plus the Sam's calls out specific types of caps by the value given (MFD for paper caps or film caps in the modern world, and mmfd for ceramic disc or mica caps.) I have some .01 MFD 630V film caps but I don't.know if the voltage is high enough, because I know a lot of times ceramic disc caps used in TVs were often times 1kV or higher rated.

.01 MFD 630V film is fine. We know what the B+ is supposed to be on the detector side, and there should be no B+ on the volume control side.

[Notimetolooz]

Vortalexfan. I've been checking on this thread from time to time and I have gathered up quite a few comments, so this is going to be a long post.
First of all, you are not doing this for money so take a break from time to time, this thread is not going away. If you are working until you are too tired you are going to make mistakes and will not be thinking straight.

You experience with the Meck is an exception not the rule. Take a look at the restoration articles at Phil's Old Radios. Lots of electrical and mechanical problems.
https://www.antiqueradio.org/restoration.htm
Also notice the thousands of posts on this forum. Do you think that if everyone just did a good job of re-capping they would not have anymore problems? Maybe they are just stupid, eh?.

Boo-hoo, school did not cover electronic repairs. Only the repair schools run by a few companies offered repair classes and for a fee. My repair knowledge is completely self taught from reading magazines like "Popular Electronics" and "Radio Electronics" (available online now) as well as books and from experience. I read many posts on the forums even if I don't have any of the units just so I can learn more. Never stop learning.

Comments like "which end of a capacitor to disconnect" shows you don't know much about how electronic components work. Your statement about DC voltage loss across a capacitor is further proof. (Capacitors do not conduct DC current.) I've suggested before that you look to sources outside this forum to learn about how electronics work (like how a tube is biased).
You comments about reversing the meter leads so that the meter would read a negative voltage as positive was nonsense, (if you did that then the positive voltages would read negative), or were you trying to be a smarta$$.

I'm sure Kevin was confused as I was with your "Alice in Wonderland" reports on the circuit measurements. They do not make sense.
When you have results that don't make sense it usually means some of you assumptions are wrong.
You THINK the meter is correct. You THINK you connections are good. You THINK you don't have any shorts. You THINK the new parts are good. You THINK you installed the new parts correctly. Something is not true.

EDIT: Anyway, I've said enough.

[vortalexfan]

Originally Posted by Kevin Kuehn

.01 MFD 630V film is fine. We know what the B+ is supposed to be on the detector side, and there should be no B+ on the volume control side.

OK, well I'm going to just take a break from these TVs for a while and work on some of my old radios for the time being. I'm so close with these TVs but like I said there's still a few bugs with the tuner and audio on them yet that need to be worked out and I'm afraid I might screw these up if I don't take a break on them.

[vortalexfan]

Ok so I slept on it a little bit and came back this morning and I went back and checked my voltages again, and the B+ voltage going to C3B and R54 and R56 is around 210V (which I'm going to chalk that up to the fact that the voltages in the Sam's are taken using a VTVM and I was using a DMM which might be why the voltages I'm measuring are a little off) and then the voltage going to pin 7 of the 3BN6 tube is around 145V which is only 10V higher than the voltage given for that pin in the Sam's (again I'm going to attribute that to the fact that I'm not using a VTVM here.)

But I'm still getting some funky readings on the output tube yet which I'm still kind of stumped about, I'm still getting NEGATIVE voltages on pins 5 and 6 of the 6AQ5 tube and also on pin 2 as well (and yes NOTIMETOLOSE I understand that doesn't make sense to you but that is what I am getting.)

I understand that the 6AQ5 tube is supposed to be self-biasing but whatever is in this TV's circuitry to make the tube do that doesn't appear to be working right otherwise I wouldn't be getting those funky voltage measurements and I would be getting a thunderous roar of white noise out of the speaker on the TV but that's not the case, the TV is dead silent, and I can't get the tuner to pull in the signal from my RF Modulator box which is being fed a signal from a DVD Player.

Before you guys ask, yes my RF Modulator works, I had it working on my Meck TV about a month ago so no its not my RF Modulator.

[vortalexfan]

UPDATE: Ok I read through some articles online (outside of here) about how self-biasing tube circuits work, so R57 which is a 680 Ohm 1W 10% tolerance resistor is the bias resistor, and I measured its resistance and it currently measures at around 753 Ohms which I think is a bit high for that application, would an out of tolerance bias resistor screw up the audio circuit, and give me the funky voltage readings I'm getting?

If so it seems I managed to figure it out on my own, which is what you were wanting me to do.

[Kevin Kuehn]

Most DMM have an input resistance of at least 1meg, so using your DMM would not significantly change the voltage reading from what Sams got using a VTVM. There are however notes on the Sams schematic stating the control settings they used when making measurements. That's because some voltages can vary with different control settings.

Your 5AQ5 680 ohm cathode resistor is not out far enough to cause a serious bias issue. But you do need a known good tube in there to move forward. I would think your 6AQ5 would work, if it is in fact a good one.

What perplexes me is how you seem to enjoy back paddling. Last we heard you said the funky negative voltages went away when you temporarily removed C50(.01uf). It was suggested that you remove that cap to correct the negative voltage situation. Have you done so, or replaced it with a know good cap? And if so what was the outcome? Now you're right back to wondering willy-nilly without a clue or sense of direction. I'm trying to provide you a sense of guidance, but like they say you can lead a horse to water, but..

[vortalexfan]

Originally Posted by Kevin Kuehn

Most DMM have an input resistance of at least 1meg, so using your DMM would not significantly change the voltage reading from what Sams got using a VTVM. There are however notes on the Sams schematic stating the control settings they used when making measurements. That's because some voltages can vary with different control settings.

Your 5AQ5 680 ohm cathode resistor is not out far enough to cause a serious bias issue. But you do need a known good tube in there to move forward. I would think your 6AQ5 would work, if it is in fact a good one.

What perplexes me is how you seem to enjoy back paddling. Last we heard you said the funky negative voltages went away when you temporarily removed C50(.01uf). It was suggested that you remove that cap to correct the negative voltage situation. Have you done so, or replaced it with a know good cap? And if so what was the outcome? Now you're right back to wondering willy-nilly without a clue or sense of direction. I'm trying to provide you a sense of guidance, but like they say you can lead a horse to water, but..

Well my comments are due to the fact that it seems that my comments have upset certain folks on here and because of that I was trying to take their feelings into account (read notimetolose on post #239) and because of that I didn't want to have to read through anymore rant posts from people who were upset at how I was going about troubleshooting this TV (notimetolose's exact words were that I was making no sense and that I was being a smartass and that I have no idea what I'm doing when it comes to using test equipment which is not true.)

So that's why I'm trying to be more careful with my comments.

Anyways the reason why I went down the cathode bias resistor route was because you kept on referring to the fact that the Audio Output tube in this TV is Cathode-Biased (Self-Biasing) and so I was trying to look into that aspect of the circuit as to why my audio circuit wasn't working right and the voltages were not right.

So yet again it seems that I misread the situation when it came to reading your comments and what you were suggesting that I look into.

I was noticing that you like to throw out subtle clues in your posts when it comes to helping people troubleshoot circuit issues (sort of a way of telling a person what the issue is without actually telling them what it is outright so that they can figure it out on their own.)
I first noticed that when you were helping me with that Meck TV when I was having the issues with the dead short in the B+ circuit in that TV, you told me in a subtle manner to double check the polarity of the filter caps for the B+ circuitry (the big ones that were installed under the chassis originally that had the electrical tape around them) and at first when I looked at how they were installed they seemed correct in how they were installed but then one of the caps vented on me and then I looked at it again and I realized that I had the caps installed positive to positive and negative when it needed to be positive to negative in that situation and when I installed it correctly it was fine, but I wouldn't of figured it out without those subtle hints.

[old_coot88]

Originally Posted by vortalexfan

...I went back and checked my voltages again, and the B+ voltage going to C3B and R54 and R56 is around 210V...

OK. That's close enough for now. At least you've verified B+ on C3b.

The identical voltage should be appearing on pin 6 (screen grid) of the 5AQ5, and on the bottom of the output xfmr primary (red lead).

In other words, there should be solid continuity (zero ohms) twixt all those points. (Forget the negative voltage issue for now) Main thing is to find out what connection's gone open.

With the set OFF, and an ohmmeter set to RX1, connect the black lead to pin 6. With the other lead, check for zero ohms to bottom of xfmr primary (red lead), and to C3b. You'll probably find the connection to C3b is what's open.

BTW, also check the xfmr primary for a few hundred ohms between pins 6 and 5 (plate) of the 5AQ5.

Once this is all sorted out, check for solid continuity (zero ohms) from C3's can to ground. Any resistance here could be contributing to the 'negative voltage' condition.

[vortalexfan]

Originally Posted by old_coot88

OK. That's close enough for now. At least you've verified B+ on C3b.

The identical voltage should be appearing on pin 6 (screen grid) of the 5AQ5, and on the bottom of the output xfmr primary (red lead).

In other words, there should be solid continuity (zero ohms) twixt all those points. (Forget the negative voltage issue for now) Main thing is to find out what connection's gone open.

With the set OFF, and an ohmmeter set to RX1, connect the black lead to pin 6. With the other lead, check for zero ohms to bottom of xfmr primary (red lead), and to C3b. You'll probably find the connection to C3b is what's open.

BTW, also check the xfmr primary for a few hundred ohms between pins 6 and 5 (plate) of the 5AQ5.

Once this is all sorted out, check for solid continuity (zero ohms) from C3's can to ground. Any resistance here could be contributing to the 'negative voltage' condition.

OK, I think I may have figured it out, and I should have figured it out sooner, because I had this issue before with the old GE tombstone radio I was working on previously, but I think maybe the negative lead of C3B isn't actually making contact with the chassis (its soldered in place but its not actually contacting the chassis its just "floating" there.

I'll check for sure when I get a chance, right now I'm trying to help my parents clean up water in the basement of their new house because the irrigation system backflow burst on them last night because it froze (because they forgot to turn the water off to the irrigation system before it started getting cold, because this was the first time they've had an in-ground irrigation system in a house so they didn't know you had to shut the water off to it.)

I may be slow on the uptake but I do eventually figure it out.

[old_coot88]

Originally Posted by vortalexfan

...I think maybe the negative lead of C3B isn't actually making contact with the chassis (its soldered in place but its not actually contacting the chassis its just "floating" there.

If the can IS actually floating electrically, it needs to be fixed as the first (not last) order of business. But there's still the separate issue of zero plate and G2 voltage (on pins 5 and 6 of the 5AQ5), as discussed previously. This wouldn't be caused by the floating can.

[vortalexfan]

Originally Posted by old_coot88

If the can IS actually floating electrically, it needs to be fixed as the first (not last) order of business. But there's still the separate issue of zero plate and G2 voltage (on pins 5 and 6 of the 5AQ5), as discussed previously. This wouldn't be caused the floating can.

1.) Yes, exactly, I do need to fix the floating negative on my replacement cap that I used to replace C3B that was in the can, and the floating negative lead would definitely cause my negative voltage readings in the audio circuitry.

2.) Yes I do still need to figure out the issue with the low voltage readings on pins 5 and 6 of the 6AQ5 tube socket and the none existing cathode voltage (which should be 17 volts but measures a measly 5 mV.)

3.) As for the floating ground issue, it is easy enough to do especially when you're trying to tie a new individual electrolytic cap negative lead onto a previously used chassis ground tie point that has tons of old solder already blobbed onto it.