Old Muntz TV for sale Locally to me, Should I pick it up?

[jr_tech]

There is also a possibility that the sagging/blooming high voltage slump is caused by downstream problems such as a weak horizontal output or damper tube, or perhaps the horizontal frequency being way off. In such a situation, a good strong 1B3 might worsen the symptoms, while a weak one might act as a current limiter.

I would not pitch any 1B3s biased on performance in this semi-working set.

jr

[Kevin Kuehn]

Originally Posted by jr_tech

There is also a possibility that the sagging/blooming high voltage slump is caused by downstream problems such as a weak horizontal output or damper tube, or perhaps the horizontal frequency being way off. In such a situation, a good strong 1B3 might worsen the symptoms, while a weak one might act as a current limiter.

I would not pitch any 1B3s biased on performance in this semi-working set.

jr

One could tweak the horizontal frequency slug and see if there's improvement.

[Electronic M]

Originally Posted by Kevin Kuehn

One could tweak the horizontal frequency slug and see if there's improvement.

Given the set currently has a good raster I'd recommend leaving the horizontal and HV system alone until video is made to work...If the horizontal looks off frequency with video adjust it, but don't risk messing it up until there is a clear and obvious problem.

Once he has video any small to moderate issues can be accurately assessed with a test pattern, followed by localized troubleshooting...

[old_coot88]

Originally Posted by Electronic M

Given the set currently has a good raster I'd recommend leaving the horizontal and HV system alone until video is made to work...If the horizontal looks off frequency with video adjust it, but don't risk messing it up until there is a clear and obvious problem.

Absolutely. Always tackle the most obvious problem foist.

[Kevin Kuehn]

Oh but it's so tempting to tweak.

[vortalexfan]

Well I'm back from my weekend trip to West Virginia, so now I will go ahead and begin more troubleshooting on this TV.

[vortalexfan]

Originally Posted by Kevin Kuehn

Also, leaving the 1 meg carbon comp resistor going to the CRT anode button original is asking for trouble. Only after you change it will you know if it's contributing to your voltage sag.

Tuner voltage issue - Looking at Sams schematic the tuner gets it's b+ from the voltage derived on the cathode(pin 8) of the 6V6 audio output tube(V12). A starting point would be to measure V12 pin 8 relative to ground, then R13 feeds that voltage to the tuners RF amp, mixer, and oscillator. So verify that you have the same voltage on one side of R13 as you do on pin 8 of V12. Next measure on the opposite side of R13 and see how much lower the b+ is at that point. Then from that point forward, R10 splits off b+ to the mixer tube( one half of V2) and R12 feeds b+ to the oscillator(the other half of V2). So measuring on both sides of those 3 resistors(all referenced to ground) should give some indication of where you're dropping too much b+ to the tuner.

**[edit]**

I just noticed R13 is under the main chassis(near the tuner), but R10 and R12 are inside the tuner, so would require removing the tuner cover to measure. If you get lucky, and actually the most likely is the problem will show up right around R13. According to your earlier voltage measurements there's not much drop in voltage between the 6AK5 and 6J6.

I just measured the Voltage from Pin 8 of the 6V6 in reference to Chassis Ground and I got 158.4 VDC and then on the input side of R13 I got 158.4 VDC as well, and then on the output side of R13 I got 154.4 VDC so only a 4 VDC drop between Pin 8 of the 6V6 tube and R13's output side.

I already have the cover removed on the tuner so I just need to figure out which resistors in the tuner are R10 and R12, so I can measure them.

[Kevin Kuehn]

Originally Posted by vortalexfan

I just measured the Voltage from Pin 8 of the 6V6 in reference to Chassis Ground and I got 158.4 VDC and then on the input side of R13 I got 158.4 VDC as well, and then on the output side of R13 I got 154.4 VDC so only a 4 VDC drop between Pin 8 of the 6V6 tube and R13's output side.

I already have the cover removed on the tuner so I just need to figure out which resistors in the tuner are R10 and R12, so I can measure them.

Apparently something has changed since you measured last with the tubes out. Try measuring again from the top on pins 5 and 6 of the 6AK5, with the tube out, still in reference to ground.

[vortalexfan]

Originally Posted by Kevin Kuehn

Apparently something has changed since you measured last with the tubes out. Try measuring again from the top on pins 5 and 6 of the 6AK5, with the tube out, still in reference to ground.

Well the only thing different was that the tubes were installed in the tuner when I took those measurements of Pin 8 of the 6V6 and input and output sides of R13, other than that nothing has changed circuitry wise in this TV.

[Kevin Kuehn]

Originally Posted by vortalexfan

Well the only thing different was that the tubes were installed in the tuner when I took those measurements of Pin 8 of the 6V6 and input and output sides of R13, other than that nothing has changed circuitry wise in this TV.

I don't see a problem with the voltages you just measured, but they don't seem to line up with what you reporting earlier with the un-tubed tuner socket pin voltages being so low.

[vortalexfan]

Originally Posted by Kevin Kuehn

I don't see a problem with the voltages you just measured, but they don't seem to line up with what you reporting earlier with the un-tubed tuner socket pin voltages being so low.

Would possibly using the wrong tube in the tuner cause some issues?

I ask because I have been subbing a 6AK5 in place of a 6AG5 tube in the tuner and I wonder if using a substitute tube rather than the original tube that it calls for in the circuit could be causing my tuner not to work right...

I know the tuners in these early TVs were quite finicky about how they worked.

[Kevin Kuehn]

Originally Posted by vortalexfan

Would possibly using the wrong tube in the tuner cause some issues?

I ask because I have been subbing a 6AK5 in place of a 6AG5 tube in the tuner and I wonder if using a substitute tube rather than the original tube that it calls for in the circuit could be causing my tuner not to work right...

I know the tuners in these early TVs were quite finicky about how they worked.

Sams schematic actually shows a 6AK5 for the RF amp. Double check the voltages again from the top side of the tuner sockets and see if they are still as low as before. Leave the tuner tubes out just like you did before.

[vortalexfan]

Originally Posted by Kevin Kuehn

Sams schematic actually shows a 6AG5 for the RF amp. Double check the voltages again from the top side of the tuner sockets and see if they are still as low as before. Leave the tuner tubes out just like you did before.

Yes I know, but I've been using a 6AK5 because I don't have any 6AG5s currently.

As for testing the tube socket voltages, I'll do that again and see what I get, which pins should I test?

[Kevin Kuehn]

Originally Posted by vortalexfan

Yes I know, but I've been using a 6AK5 because I don't have any 6AG5s currently.

As for testing the tube socket voltages, I'll do that again and see what I get, which pins should I test?

I meant they show a 6AK5. For starters just measure the plate pins, that's where we're looking for B+.

[Kevin Kuehn]

While you're at it try turning thought the channels and see if that changes the voltage. I just looked back at your earlier photo and that tuner has a major rust deposit on top. If mice were peeing on it, it could be there's a real mess down in the contacts.