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

[static1701]

It really is best to take your schematic and measure the voltage at the different points, You will find the problem that way. I was working on an amplifier the other day that had no sound after replacing the capacitors and as I traced the power from the capacitors, I found that both resistors that feed the plates of the phase inverter tube were open. Replaced them and had sound. You can't tell by looking, and you can't test parts while they are in the circuit. As for smoke coming out of something, replace the part. I had that happen on my predicata. At the age of the tv's we work on, all capacitors and resistors should be replaced, unless a tube is shorted or really bad... it will serve well enough for testing, you don't have to have a perfect one. Looking forward to seeing a picture of your set working.

[Electronic M]

If you pull the vertical output tube too and it still draws close to rated power (as I suspect it will) you still need to finish troubleshooting the power supply...Like I said the social coil circuit could be an issue...also depending on where that 390 ohm resistor is in circuit whatever is causing it to smoke is also a likely cause of the overload.

[Kevin Kuehn]

Originally Posted by Electronic M

If you pull the vertical output tube too and it still draws close to rated power (as I suspect it will) you still need to finish troubleshooting the power supply...Like I said the social coil circuit could be an issue...also depending on where that 390 ohm resistor is in circuit whatever is causing it to smoke is also a likely cause of the overload.

social coil circuit?

R62(390 ohm) is the plate load resistor for the 6V6 audio out(Sams calls it a filter). It supplies voltage from the wiper of the focus coil to the 6V6 plate circuit. This set uses the audio output stage as a voltage dropper, similar to Admiral sets of the time. It's plate voltage(pin 3) should be 205vdc referenced from the cathode(pin 8). Confusing as all get-out to troubleshoot. As mentioned above, best to follow Sams voltage measurement chart to isolate the problem area.

[Electronic M]

Originally Posted by Kevin Kuehn

social coil circuit?

R62(390 ohm) is the plate load resistor for the 6V6 audio out(Sams calls it a filter). It supplies voltage from the wiper of the focus coil to the 6V6 plate circuit. This set uses the audio output stage as a voltage dropper, similar to Admiral sets of the time. It's plate voltage(pin 3) should be 205vdc referenced from the cathode(pin 8). Confusing as all get-out to troubleshoot. As mentioned above, best to follow Sams voltage measurement chart to isolate the problem area.

Focus coil.

My smart-ass-phone has an overly aggressive autocorrect baked into it's typing utility and it likes to substitute different words for correctly spelled ones when it thinks I didn't use the right one in sentence context...it drives me nuts sometimes, and is even worse for brand name that were gone before my generation and TV service lingo that is otherwise dead.
There are also times it will botch a word in messages to friends and I'll retype the word to make it make sense and it will change it when I push send.... infuriating.

[vortalexfan]

Originally Posted by Electronic M

My smart-ass-phone has an overly aggressive autocorrect baked into it's typing utility and it likes to substitute different words for correctly spelled ones when it thinks I didn't use the right one in sentence context...it drives me nuts sometimes, and is even worse for brand name that were gone before my generation and TV service lingo that is otherwise dead.
There are also times it will botch a word in messages to friends and I'll retype the word to make it make sense and it will change it when I push send.... infuriating.

I also have issues with spell checker on my phone, although not nearly as bad as yours, and I agree it's infuriating.

I'll take a look at some more voltages.

[vortalexfan]

OK so this is weird but going across pins 3 and 6 on the 6T8 tube on the TV there is a 30 Ohm dogbone resistor that doesn't show up anywhere on the sams and it measures open which might be part of the reason why this TV has no audio as the 6T8 in this TV functions as the Phase Inverter for the 6V6 tube as well as the Audio Frequency Amplifier and the Ratio Detector Tube, and that dog bone resistor looks factory (which I know sometimes there were little changes made to these old electronics at the factory that weren't always put into the sams because they were done after the Sams were made.)

The other resistors on the 6T8 Tube which goes across pins 2 and 6 (which are the plates of the tube) measure nearly spot on.

so that open 30 Ohm dog bone resistor might be part of the reason why I have no audio.

As for the voltage and resistance readings on the tube sockets, the resistance readings on the 5U4 tube are are a little high, pins 2 and 8 which should measure around 22k ohms measures around 32k ohms and then pins 4 and 6 should measure around 68 Ohms but instead measure around 72 ohms.

That measurement was taken without the tube in the socket and the set powered off.

[Kevin Kuehn]

Don't worry about the 6T8, it has no bearing on your power supply issue and in fact you can remove it from it's socket if it's bothering you. So did you measure the voltages on the 6V6 audio output tube?

[Electronic M]

By the late 40s some pF range capacitors were made on tubular ceramic forms and color coded....they look just like dogbone resistors but really are dogbone capacitors....If it's presence bothers you check the schematic for capacitors connected in the way it is.

[jr_tech]

Originally Posted by Electronic M

By the late 40s some pF range capacitors were made on tubular ceramic forms and color coded....they look just like dogbone resistors but really are dogbone capacitors....If it's presence bothers you check the schematic for capacitors connected in the way it is.

Likely the 3 uuf cap shown between pin 3 and ground....I suspect that pin 6 was used as a tie point.

jr

[vortalexfan]

Originally Posted by Kevin Kuehn

Don't worry about the 6T8, it has no bearing on your power supply issue and in fact you can remove it from it's socket if it's bothering you. So did you measure the voltages on the 6V6 audio output tube?

No, I didn't yet.

But I did figure out that pretty much all the resistors in the audio circuit that are associated with the 6V6 and the 6T8 tube are all measuring bad (either way high or open), also the 6,000 ohm 10% 20 Watt wirewound resistor that's part of the HV section is measuring open as well in the Sams its called the Damper Filter-Wirewound, which might be why I'm not getting any HV and also might be part of what's causing the TV to motorboat.

[vortalexfan]

Originally Posted by jr_tech

Likely the 3 uuf cap shown between pin 3 and ground....I suspect that pin 6 was used as a tie point.

jr

Yep that's what it was, and it measures within tolerance so I'm leaving it alone.

But all the resistors around it are all out of tolerance or measure open, so they're all getting replaced.

[Kevin Kuehn]

Originally Posted by vortalexfan

No, I didn't yet.

But I did figure out that pretty much all the resistors in the audio circuit that are associated with the 6V6 and the 6T8 tube are all measuring bad (either way high or open), also the 6,000 ohm 10% 20 Watt wirewound resistor that's part of the HV section is measuring open as well in the Sams its called the Damper Filter-Wirewound, which might be why I'm not getting any HV and also might be part of what's causing the TV to motorboat.

You reported a few posts back that you had a raster, before R62 smoked, so at that point you had HV. All I can say is that there's been a whole lot of smoking going on.

[jr_tech]

Originally Posted by vortalexfan

But all the resistors around it are all out of tolerance or measure open, so they're all getting replaced.

Do you check all of the new resistors before you do the replacement... Once in a while a new resistor will be bad or mis-labeled. It is also interesting to recheck the old resistors after removal, to verify your diagnosis.

jr

[vortalexfan]

Originally Posted by jr_tech

Do you check all of the new resistors before you do the replacement... Once in a while a new resistor will be bad or mis-labeled. It is also interesting to recheck the old resistors after removal, to verify your diagnosis.

jr

Yes to both, my new resistors tested within spec (they are 5% tolerance resistors) and the old resistors tested way out of spec and or open, and that is the case with almost all of the resistors in this TV it seems and I'm going to have to order some resistors as well because there were some resistor values in the set that I didn't have in my resistor stash like 180k Ohm, 2.2M Ohm, etc.

Most of the resistors in the set I have already fortunately, just a few oddball values that I don't have in my stash I'm gonna have to order.

[vortalexfan]

Here's a couple of the capacitors that were inside the TV some Cornell-Dubilier "Tiny Chief" Capacitors!