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

[vortalexfan]

Originally Posted by Kevin Kuehn

Are you measuring C49 out of circuit? And even if C49 were open it would have no influence on the weird B+ voltages you're reporting. I'd say it's nothing more than a RF filter to the audio signal leaving the detector plate.

Next definitely for sure possibility please.

Well that capacitor though is where my voltages to the audio output circuit are getting lost though for sure because I measured the B+ voltage from the terminal that C49 ties to and goes to ground and I have B+ voltage there going to ground but then when I measure from that point to the other side of C50 the 10,000 pF ceramic disc cap there's no voltage there (it's -20V or so) and that is supposed to supply the voltages to pins 5 and 6 of the 6AQ5 tube, and yes I did replace C50 with a new capacitor finally and that didn't change the voltage readings any.

[Kevin Kuehn]

Originally Posted by vortalexfan

Yes I did use a 450V cap there, but it is rated for 550V surge so it should be fine.

It wouldn't be a bad idea to measure your B Boost directly across that cap. My Bugeye's B Boost runs around 475v with it's decrepit selenium rectifiers still in it and 117 AC line voltage.

[Kevin Kuehn]

Originally Posted by vortalexfan

Well that capacitor though is where my voltages to the audio output circuit are getting lost though for sure because I measured the B+ voltage from the terminal that C49 ties to and goes to ground and I have B+ voltage there going to ground but then when I measure from that point to the other side of C50 the 10,000 pF ceramic disc cap there's no voltage there (it's -20V or so) and that is supposed to supply the voltages to pins 5 and 6 of the 6AQ5 tube, and yes I did replace C50 with a new capacitor finally and that didn't change the voltage readings any.

Let's get one thing straight here. B+ is not suppose to get to pins 5 and 6 of the 6AQ5 through C50. C50 is a audio signal coupling cap to the top of the volume control. C50's function is to pass the audio signal from the plate of the detector to the audio output grid. A capacitor is used because it's intended to block the B+ feeding the plate of the detector tube from getting into the grid circuit of the 6AQ5.

[vortalexfan]

Originally Posted by Kevin Kuehn

It wouldn't be a bad idea to measure your B Boost directly across that cap. My Bugeye's B Boost runs around 475v with it's decrepit selenium rectifiers still in it and 117 AC line voltage.

Ok, and would replacing those old selenium rectifiers with a couple of 1N4007 diodes be a suitable replacement? If so do I need to add or change some voltage dropping resistors in the circuit?

[vortalexfan]

Originally Posted by Kevin Kuehn

Let's get one thing straight here. B+ is not suppose to get to pins 5 and 6 of the 6AQ5 through C50. C50 is a audio signal coupling cap to the top of the volume control. C50's function is to pass the audio signal from the plate of the detector to the audio output grid. A capacitor is used because it's intended to block the B+ feeding the plate of the detector tube from getting into the grid circuit of the 6AQ5.

Well either way I'm not getting any audio out of the TV and I'm still not getting the 200+ volts I need to be getting on pins 5 and 6 of the 6AQ5 tube that the Sam's calls out and I'm not getting 17V on pin 2 of the 6AQ5 either, so I'm still stumped as to what's going on with the audio section of this TV, and I've still got no signal from the tuner to the TV on here either.

[Kevin Kuehn]

Originally Posted by vortalexfan

Well either way I'm not getting any audio out of the TV and I'm still not getting the 200+ volts I need to be getting on pins 5 and 6 of the 6AQ5 tube that the Sam's calls out and I'm not getting 17V on pin 2 of the 6AQ5 either, so I'm still stumped as to what's going on with the audio section of this TV, and I've still got no signal from the tuner to the TV on here either.

Reread post #245 where you had 210v at C3B. You need to follow that point to pins 5 and 6 of your 6AQ5 and see where you loose the 210V. Follow the schematic and ohm everything out. One path is from C3B positive to pin 6(screen), the other is C3B positive to the bottom(red) wire of the output transformer primary. B+ needs to go in on the red wire of the primary winding and exit on the blue wire to pin 5(plate) of the 6AQ5. If there's no connections where there should be, something has become open or otherwise mis-wired.

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.

[Edit] Here's a picture of the bottom side of my working chassis showing the 5AQ5(6AQ5) connections so you can compare your wiring.

[vortalexfan]

Originally Posted by Kevin Kuehn

Reread post #245 where you had 210v at C3B. You need to follow that point to pins 5 and 6 of your 6AQ5 and see where you loose the 210V. Follow the schematic and ohm everything out. One path is from C3B positive to pin 6(screen), the other is C3B positive to the bottom(red) wire of the output transformer primary. B+ needs to go in on the red wire of the primary winding and exit on the blue wire to pin 5(plate) of the 6AQ5. If there's no connections where there should be, something has become open or otherwise mis-wired.




[Edit] Here's a picture of the bottom side of my working chassis showing the 5AQ5(6AQ5) connections so you can compare your wiring.

Well besides the fact that your TV's wiring is in much better shape than mine is (the color is faded from my TV's wiring) I don't see anything different from yours and mine except that it seems you still kept some of the original can caps in circuit whereas mine are all replacent capacitors.

I really don't know what's going here.

[Kevin Kuehn]

Originally Posted by vortalexfan

Well besides the fact that your TV's wiring is in much better shape than mine is (the color is faded from my TV's wiring) I don't see anything different from yours and mine except that it seems you still kept some of the original can caps in circuit whereas mine are all replacent capacitors.

I really don't know what's going here.

I sawed the top off my cans and re-used the old terminals. Any chance you can post a close up of the underside of your chassis around the 6AQ5, including your filter caps? Sometimes it helps to have a fresh set of eye's look things over.

[vortalexfan]

Originally Posted by Kevin Kuehn

I sawed the top off my cans and re-used the old terminals. Any chance you can post a close up of the underside of your chassis around the 6AQ5, including your filter caps? Sometimes it helps to have a fresh set of eye's look things over.

Ok, I wondered about that. I'll get you a picture of my 5 (6)AQ5 tube section of the TV and the replacement electrolytics.

[vortalexfan]

I'll have to do it when I get home from work because I'm at work right now. I meant to include this in my initial post but forgot to, I'm adding it as an additional posting because I know you don't like it when I edit my posts multiple times to add additional information.

[vortalexfan]

OK so here's some pictures of the Audio Section of my Zenith Bugeye TV, and of all of the Electrolytic caps I replaced in the TV.

I added some visual markers and texts to each of the photos so you can tell what's what in each photo.

See pictures below.

[Kevin Kuehn]

Originally Posted by vortalexfan

OK so here's some pictures of the Audio Section of my Zenith Bugeye TV, and of all of the Electrolytic caps I replaced in the TV.

I added some visual markers and texts to each of the photos so you can tell what's what in each photo.

See pictures below.

I think I see a problem but it's tough to see everything in your photo. Take a look at my orange circled area's. All 3 circled points should be interconnected. Inside the largest circle there should be 4 items soldered together. The + side of C3B, the right lead from R56(470 ohm feed from B+), left lead of R54(390k), and a orange wire should head over to the second solder pocket from the right end of the terminal strip directly below the 6AQ5 socket. From that same solder pocket another orange wire should be connected to pin 6 of the 6/5AQ5, and also the red lead from the audio output transformer should be soldered into that same pocket. But specifically I can't see any wire coming over to that solder pocket from the positive end of C3B(large circled point)? You can reference the photo from my set. In any event that's the path B+ needs to follow to get from C3B over to the audio output tube.

[dieseljeep]

Originally Posted by Kevin Kuehn

I sawed the top off my cans and re-used the old terminals. Any chance you can post a close up of the underside of your chassis around the 6AQ5, including your filter caps? Sometimes it helps to have a fresh set of eye's look things over.

Rather impressive! How do you cut the cans so perfect?
Bought and sold a set like that about 60 years ago. Mine was an earlier model that used a 3BY6 instead of the better circuit using a 3BU8.
The outward appearance was similar.

[Kevin Kuehn]

Originally Posted by dieseljeep

Rather impressive! How do you cut the cans so perfect?
Bought and sold a set like that about 60 years ago. Mine was an earlier model that used a 3BY6 instead of the better circuit using a 3BU8.
The outward appearance was similar.

Thanks. I actually removed these and used my band saw. Then a few passes over 220 grit on a flat surface squares the end. Seems like a lot of work, but by using a very large (radiator sized ) soldering iron I'm able to heat the ground lugs and squeeze them straight with a flat nose pliers, then carefully wiggle them free. Space permitting you certainly could hack them off using a Zona saw while they're still attached to a chassis.

[vortalexfan]

Originally Posted by Kevin Kuehn

Thanks. I actually removed these and used my band saw. Then a few passes over 220 grit on a flat surface squares the end. Seems like a lot of work, but by using a very large (radiator sized ) soldering iron I'm able to heat the ground lugs and squeeze them straight with a flat nose pliers, then carefully wiggle them free. Space permitting you certainly could hack them off using a Zona saw while they're still attached to a chassis.

OK, so I looked over my chassis after you mentioned the missing wire and sure enough, I'm not sure how I missed it but I forgot to put that wire back in when I removed it from the old can cap to install the new one, I now have the voltages back in the audio section, and its functioning as it should.

But now I have a new problem, one of my Video IF tubes was bad (which is why I'm not getting anything from the tuner) which is a 3CB6 and I tried subbing in a 6CB6 (because I have a whole butt load of them) and it seems the TV doesn't like them, because they just glow white and then just die after 3 seconds (and it doesn't matter which 3CB6 socket its stuck in, it does the same thing in all 3 sockets) and I was hoping I could get away with not having to order a new tube for the TV (as I don't have any 3CB6 tubes in my stash.)

Is it normal for a 6.3V Tube to glow white hot and then burn out after 3 seconds in a socket originally meant for a 3V tube in a series string set?
I was thinking that it was possible to install a higher voltage tube in a lower voltage tube spot in series string radios and TVs (like how you can sub in place of a 35L6 a 50L6 on old Series string radios and it would run fine.)

Am I missing something here?