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

[vortalexfan]

Originally Posted by Electronic M

If the can wafer wasn't busted, and you had a 75W soldering iron I'd have suggested using the terminal strip you have and soldering the mount tab of the strip to the negative terminal lug of the can(instead of bolting it to chassis)....I do this sometimes and as long as you have a big iron and make a solid solder joint it works pretty nice. Some might complain it is not original workmanship but as long as it isn't a high buck set stuff like this doesn't make much difference.

I think I will just completely remove the old can capacitor completely out of the TV and just bolt a proper terminal strip down onto the chassis and just wire it up and go from there. Since the original filter cap was a 40/40/40 @ 450 VDC capacitor I don't think it will matter where I hook up the positive leads.

[vortalexfan]

OK So as luck would have it the tube socket for my Video Amp circuit on my TV is got a couple of damaged pins and I need a new tube socket, its an octal tube socket that mounts from below.

it looks like the one pictured in the link below.

https://www.tubesandmore.com/product...unting-centers

It also seems that I'll need a new 6AC7 tube as well for the Video Amp on my TV as one of the pins on the tube is broken.

[dieseljeep]

Originally Posted by vortalexfan

OK So as luck would have it the tube socket for my Video Amp circuit on my TV is got a couple of damaged pins and I need a new tube socket, its an octal tube socket that mounts from below.

it looks like the one pictured in the link below.

https://www.tubesandmore.com/product...unting-centers

It also seems that I'll need a new 6AC7 tube as well for the Video Amp on my TV as one of the pins on the tube is broken.

If the original socket is one of those molded bakelite jobs, try to find a scrap chassis with the same kind of socket and steal the contacts from it. It's easy enough to do. The only ones you cant repair is the flat phenolic wafer type.

[Electronic M]

Originally Posted by dieseljeep

If the original socket is one of those molded bakelite jobs, try to find a scrap chassis with the same kind of socket and steal the contacts from it. It's easy enough to do. The only ones you cant repair is the flat phenolic wafer type.

+1 Saves a lot of effort doing it that way. Takes a bit of skill to get the donor contact out intact especially if it was soldered, but still much easier than a socket swap.

[Electronic M]

Possible but highly unlikely.

To troubleshoot this (and I have had to troubleshoot similar issues before) disconnect the B+ rail and filter cap connection to your the 5U4 (remove all load from it). If it stops arcing you have confirmed the B+ rail has a short or severe overload. If it continues to arc with no load then the socket may have a short or the transformer may be supplying too high an AC voltage.

Assuming the arcing stopped reconnect the first filter cap then reconnect small parts of the B+ 1 at a time (not all at once) the first one to cause arcing is your short, and you'll have to pick it over with a fine tooth comb to find the root cause.

I've fought a few B+ shorts. Sometimes they are obvious if you look everywhere, sometimes they are hidden... Case in point: a 40s zenith chassis with only a couple rubber wires in seemingly good shape...the single rubber wire feeding the eye tube had one dry patch of insulation that had disintegrated right at the eyelet where it passed through the chassis, and was invisibly shorting to chassis there... just because you can't see a problem, and have replaced the likely suspects doesn't mean the problem isn't there.

[Kevin Kuehn]

All the electrolytic caps should be replaced, dry or not. Over time the dielectric breaks down just like the paper caps do. That 500 mfd cap can be replaced with a 470 mfd. Voltage rating can be higher, say a modern 25v shouldn't be much bigger than the original.

[vortalexfan]

Originally Posted by Kevin Kuehn

All the electrolytic caps should be replaced, dry or not. Over time the dielectric breaks down just like the paper caps do. That 500 mfd cap can be replaced with a 470 mfd. Voltage rating can be higher, say a modern 25v shouldn't be much bigger than the original.

I checked the Sam's for this TV and I Figured out that the 500 MFD 5 VDC Capacitor is the Bias Filter Capacitor, so it seems that if that capacitor has indeed failed like I am suspecting that it did, then it could very well be the source of my 5U4G's Arcing problems.

Would a 470 MFD 6.3 VDC electrolytic cap work as a replacement for this capacitor?

Also there's a 100 MFD 150 VDC capacitor that was a replacement at some point for C7 which was a 100 MFD 25 VDC electrolytic capacitor that must of failed at some point in time.
The strange thing is that when they hooked up the negative lead on that capacitor instead of using using the floating ground rail on one of the tube sockets or something they hooked the negative lead of that electrolytic to the chassis, which might also be causing some of my issues, C7 by the way according to the Sam's is the Vertical Output Tube Cathode Bypass Capacitor.

[vortalexfan]

Originally Posted by Electronic M

Possible but highly unlikely.

To troubleshoot this (and I have had to troubleshoot similar issues before) disconnect the B+ rail and filter cap connection to your the 5U4 (remove all load from it). If it stops arcing you have confirmed the B+ rail has a short or severe overload. If it continues to arc with no load then the socket may have a short or the transformer may be supplying too high an AC voltage.

Assuming the arcing stopped reconnect the first filter cap then reconnect small parts of the B+ 1 at a time (not all at once) the first one to cause arcing is your short, and you'll have to pick it over with a fine tooth comb to find the root cause.

I've fought a few B+ shorts. Sometimes they are obvious if you look everywhere, sometimes they are hidden... Case in point: a 40s zenith chassis with only a couple rubber wires in seemingly good shape...the single rubber wire feeding the eye tube had one dry patch of insulation that had disintegrated right at the eyelet where it passed through the chassis, and was invisibly shorting to chassis there... just because you can't see a problem, and have replaced the likely suspects doesn't mean the problem isn't there.

Well I'm actually wondering if that 500MFD 5 VDC capacitor is the problem because I looked at the Sam's and it says that the 500 MFD 5 VDC capacitor is the Bias Filter Capacitor, which if that's working right it may very well cause my rectifier tube arcing issue.

As for the B+ Voltage Rail and where it connects to the rectifier tube and how to test it where is that point on the Rectifier tube socket?

[Electronic M]

a 6.3V cap is a fine sub for the 5V.

The B+ connection point will be one of the 5U4 heater pins...Without the schematic in front of me, I can't tell you which, but it shouldn't be hard to figure out.

[old_coot88]

Replacing the 500mf@5V cap won't fix your problem, guaranteed. It's already got a very low resistance across it, probably 10 - 20 ohms or so (wish we could see the actual schematic). So even if the cap were dead shorted, the increased load on the power supply will be negligible.

[Kevin Kuehn]

Agree the source of your excessive current draw is not the 500 mfd cap, but it needs to go none the less. Since you apparently have the Sams folder now, how about checking out the resistance readings chart on page 8. For starters check the resistance from the 5U4 filament pins(2,8) to chassis ground. Chart says there should be approximately 22,000 ohms there.

[jr_tech]

Don’t power it up again to check voltage! There is likely a short to ground that you must identify and remedy first. Do some ohm meter tests first.

Originally Posted by Kevin Kuehn

Agree the source of your excessive current draw is not the 500 mfd cap, but it needs to go none the less. Since you apparently have the Sams folder now, how about checking out the resistance readings chart on page 8. For starters check the resistance from the 5U4 filament pins(2,8) to chassis ground. Chart says there should be approximately 22,000 ohms there.

jr

[vortalexfan]

Originally Posted by jr_tech

Don’t power it up again to check voltage! There is likely a short to ground that you must identify and remedy first. Do some ohm meter tests first.



jr

OK So testing pins 2 and 8 of the 5U4G tube socket I'm only getting 25.5 Ohms on those pins, and not the 22,000 Ohms I should be getting.

I'm guessing that means that the issues I'm having with the excessive (4.5 Amps, 520 Watts) current draw lies there somewhere?

Or is that a sign that something else further down the line is causing that excessively low filament resistance reading on my 5U4G tube socket?

[vortalexfan]

This TV has me seriously stumped, there is NOTHING in this TV that looks like it could of shorted to ground.
The 26.0 Ohm Reading I'm getting on the 5U4G rectifier tube Socket rather than the 22,000 Ohm reading I should be getting is leading me to think that perhaps my 5v winding in my power transformer had failed in some way shape or form.

Everything else measures fine and there isnt' anything else in the TV that I can see that looks to be bad, all of the resistors test within tolerance (which is surprising) and leaky capacitors wouldn't cause excessive amounts of current draw to the point that the unit is drawing 3x the current its rated for.

It can't be the power supply caps because I had already replaced those with brand new ones and was careful to observe proper polarity and its still drawing over 4 amps of current and over 500 watts of power and the 5U4G tube is still arcing so like I said this TV has me stumped I cannot for the life of me figure out whats going on with this TV.

[Electronic M]

Originally Posted by vortalexfan

OK So testing pins 2 and 8 of the 5U4G tube socket I'm only getting 25.5 Ohms on those pins, and not the 22,000 Ohms I should be getting.

I'm guessing that means that the issues I'm having with the excessive (4.5 Amps, 520 Watts) current draw lies there somewhere?

Or is that a sign that something else further down the line is causing that excessively low filament resistance reading on my 5U4G tube socket?

Are you measuring 2 to ground and 8 to ground, or measuring 2 to 8 ( 2 to 8 ain't helpful)?

Either 2 or 8 should have a choke(in series with B+) or B+ line connected to it... unsolder the B+ line or choke and check 2 and or 8 to ground resistance. If the resistance is much higher than before then you have confirmed the rect and transformer are good. You'll then have to disconnect splits on the B+ line from the main line and check b+ to ground resistance till you find the point that has the short.

Most B+ shorts happen in ways that make visually identifying the issue impossible. You gotta rely on instruments, logic guided by the schematic.

It is not impossible for paper caps to dead short and for that to effect the B+... usually there is a power resistor in series that smokes out first, but not all sets are wired the same.

If I had it on my bench I could probably isolate the short in 30 min.