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

[old_coot88]

[vortalexfan]

Originally Posted by Kevin Kuehn

Time for more voltage measurements. Does your tuner match that of the sams folder you've been using, a single 6AG5 and 6J6? If so verify that your DC pin voltages match what Sams call out for V1 and V2, from the voltage chart on page 8.

For anyone following here's the tuner portion of the Sams 101-5 schematic along with the voltage chart.

https://live.staticflickr.com/65535/...38a31f87_b.jpg

https://live.staticflickr.com/65535/...ec92c010_b.jpg

Yes, my TV has the 2 tube tuner in it.
Although I don't have any 6AG5 tubes so I subbed it out with a 6AK5 tube.

I'm assuming I can take the voltage measurements through the top of the tuner's tube sockets with the tubes removed?

[Kevin Kuehn]

Originally Posted by vortalexfan

Yes, my TV has the 2 tube tuner in it.
Although I don't have any 6AG5 tubes so I subbed it out with a 6AK5 tube.

I'm assuming I can take the voltage measurements through the top of the tuner's tube sockets with the tubes removed?

No the tubes definitely need to be installed, so I suppose that's going to be difficult unless you have one of the test socket adapters. You might be able to push the pins only partially in the socket and probe the sides of them. Maybe Old Coot will have a better idea on where to go next. I was going to suggest that you check for change in AGC voltage when you connect your signal source to the antenna input vs no signal, if so that would indicate that signal is getting though the tuner and video IF and at least as far as the detector. AGC voltage should go more negative with stronger signal. Great to hear the HV rectifier solved your brightness issue.

[old_coot88]

Have you checked for B+ going to the tuner? And can you get underneath the chassis to verify that there's B+ voltage on the plates and screens (G2s) of the video IF tubes?

[vortalexfan]

OK so here's the measurements I got from the tube sockets on the tuner in the TV:

6AG5:

What it should measure:
Pin 1: -.2 VDC
Pin 2: 0 V
Pin 3: 6.3 VAC
Pin 4: 0 V
Pin 5: 145 VDC
Pin 6: 130 VDC
Pin 7: 0 V

What I measured:
Pin 1: -0.6 VDC
Pin 2: 0 V
Pin 3: 6.8 VAC
Pin 4: 0 V
Pin 5: 83.3 VDC
Pin 6: 82.3 VDC
Pin 7: 0 V

6J6:

What it should measure:
Pin 1: 110 VDC
Pin 2: 83 VDC
Pin 3: 0 V
Pin 4: 6.3 VAC
Pin 5: -2 VDC
Pin 6: -6 VDC
Pin 7: 0 V

What I measured:

Pin 1: 80 VDC
pin 2: 74.5 VDC
Pin 3: 0 V
Pin 4: 6.8 VAC
Pin 5: .2 VDC
Pin 6: 0 V
Pin 7: 0 V

So it looks like some of my critical voltages for the tuner are a lower than they should be.

[vortalexfan]

Originally Posted by Kevin Kuehn

No the tubes definitely need to be installed, so I suppose that's going to be difficult unless you have one of the test socket adapters. You might be able to push the pins only partially in the socket and probe the sides of them. Maybe Old Coot will have a better idea on where to go next. I was going to suggest that you check for change in AGC voltage when you connect your signal source to the antenna input vs no signal, if so that would indicate that signal is getting though the tuner and video IF and at least as far as the detector. AGC voltage should go more negative with stronger signal. Great to hear the HV rectifier solved your brightness issue.

Well its kind of hard to access the tube sockets for the tuner from below because of how the tuner is setup.

and unfortunately I don't have test sockets.

I guess I could try the partially installing the tubes into the socket and probing the tubes for voltages that way.

I just now read your comment about the tubes needing to be in the socket for the voltage readings so disregard the voltage measurements I gave, because those were taken with the tubes out of the socket.

[Electronic M]

Your plate voltages should be higher with the tube out (and also because of your high line voltage) not lower. Tuner B+ is probably low. You may still have problems in your B+ system left to sort out.

[vortalexfan]

Originally Posted by Electronic M

Your plate voltages should be higher with the tube out (and also because of your high line voltage) not lower. Tuner B+ is probably low. You may still have problems in your B+ system left to sort out.

Yeah, I'll take a look into that.

I'll have to see where the B+ is sourced from for the Tuner and take some measurements from there.

[vortalexfan]

Here's a picture of what the TV's raster looks like currently.

[vortalexfan]

As you can see from the pictures there's diagnal lines scrolling across the screen and then 2 vertical "jailbars" on the left side of the screen.

But I do have a nice bright raster!

[Kevin Kuehn]

Looking good. Do those jail bars move sideways when you adjust the horizontal hold? You could try adjusting the horizontal drive and see if that has any influence. The diagonal lines are just vertical retrace which is pretty common on that period set. There's a possibly you can add a vertical blanking circuit once you get all the other bugs out. Make any headway on voltage measurements, and locate the b+ going to the tuner?

[vortalexfan]

Originally Posted by Kevin Kuehn

Looking good. Do those jail bars move sideways when you adjust the horizontal hold? You could try adjusting the horizontal drive and see if that has any influence. The diagonal lines are just vertical retrace which is pretty common on that period set. There's a possibly you can add a vertical blanking circuit once you get all the other bugs out. Make any headway on voltage measurements, and locate the b+ going to the tuner?

I have a quick question about the High Voltage Rectifier Tube.

I have 4 1B3GT HV Rectifier Tubes in my stash, the one that originally came with the TV when I got it that the only identifier marks on it are the words "VEE" stamped in red ink on the base of the tube and then the date code 9-53 stamped in red ink in the base, and then I have an RCA Branded 1B3GT Tube that's from the early 1950s, and then a Sylvania Branded 1B3GT Tube with a date code of 508 (50th week of 1948), and then a NOS IEC 1B3GT/1G3GT tube of which all of those tubes measure like brand new (the needle points squarely on 115 or so on each of them on the emissions test) on my Sencore Mighty Mite VII TC 162 Tube Tester and using the life test function on my tester the needle doesn't budge or barely budges which usually means that the tube is very good yet, and the grid leakage test measures around zero on all 4 of the tubes, but yet when I tried all 4 Tubes in my TV the tube marked "VEE" gives me the best picture out of all the tubes.

How is it possible for a tube to measure like brand new emissions wise and then perform like crap in circuit? Is it possible that my 1 Meg 1 Watt resistor in series with the picture tube anode cap could cause the High Voltage to perform like that?

And what I mean by the 1B3GT tubes performing like crap in circuit but measuring like NOS emissions wise is that when I use some of those tubes in circuit the picture cuts out when the brightness control is turned all the way up but then it comes back when its turned to the middle, but when the aforementioned tube marked "VEE" on it is in circuit the picture doesn't disappear when the brightness control is turned all the way up.

Any ideas about what could be causing that? Is it the 1 Meg 1 Watt resistor in series with the HV Anode Button for the Picture tube causing that?

Also I have not been able to get the B+ issue figured out on the Tuner yet, I tried the partially inserted tube method for measuring tube voltages like you suggested but I didn't have enough clearence under the tubes to insert my Multimeter probes.
Also the 6J6 tube has a shielded socket around it so it doesn't have any room at all for me to stick a test probe inside to get under the tube to take voltage measurements.

And no those Jailbars don't move with the horizontal hold adjustment, in fact when I adjust the horizontal hold knob I don't see any sort of difference in the horizontal adjustments.

[Electronic M]

Pretty much every tube tester made wasn't designed to subject a HV rect tube to it's designed opperating conditions so the test has very poor accuracy (to some extent that goes for dampers H outputs and HV regulators too)...
These tubes are best tested in a working chassis.

[old_coot88]

Yep, the only valid test of a HV rectifier is how well it performs in a working set. A damper may apprear to perform OK, but abruptly arc heater-to-cathode when you tap it (that's the best test for a damper tube). A horz.output tube may be slow to fill out the screen at turn-on. Yet a tube tester may show a tube 'good' in each case.

[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.