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

[vortalexfan]

Originally Posted by Tube TV

That seems quite low, some of that could be the electrolytics loading the circuit down as they charge. To me it looks like its ahead of the transformer and rectifier.
You could power it up and watch the rectifier tube for arcing, and red plating.

without that white wire attached to the 5U4 tube socket the tube doesn't arc anymore which I'm guessing means that the filter choke is bad.

[Electronic M]

Originally Posted by vortalexfan

without that white wire attached to the 5U4 tube socket the tube doesn't arc anymore which I'm guessing means that the filter choke is bad.

All it means is that the power transformer and tube, and tube socket are good (and that the short is inor down stream of L1). You need to confirm L1 is bad by unhooking both leads on the choke and measure resistance of both to ground and confirm it is a measurable/low resistance to confirm L1 is bad. If L1 is infinite resistance to ground then it is good and you still need to find the actual short.

Gotta keep dividing and conquering... you've cleared some of the more important parts, and found a a direction to follow to find the short. Keep at it.
Don't let yourself get lazy or confused.

[vortalexfan]

Originally Posted by Electronic M

All it means is that the power transformer and tube, and tube socket are good (and that the short is inor down stream of L1). You need to confirm L1 is bad by unhooking both leads on the choke and measure resistance of both to ground and confirm it is a measurable/low resistance to confirm L1 is bad. If L1 is infinite resistance to ground then it is good and you still need to find the actual short.

Gotta keep dividing and conquering... you've cleared some of the more important parts, and found a a direction to follow to find the short. Keep at it.
Don't let yourself get lazy or confused.

Ok. Just curious but can a filter choke be wired up backwards, or does it not matter which way it's wired up?

[Kevin Kuehn]

Originally Posted by vortalexfan

It was but then I switched it around once I realized it was hooked up wrong.

OK, so you switched it around. Have you powered up the set with the white wire connected back to pin 2 of the 5U4 since you switched it? If you previously had that white wire going to the negative side of the C1A, & B caps, that alone explains why the set was drawing excessive current, because that point connects to the center tap of the high voltage windings. Normally there would be 15 ohms from that point to chassis ground, which is why I suggested you also measure the resistance of R93(should be 15 ohms)

Originally Posted by vortalexfan

I powered it up with that white wire disconnected from the 5U4 tube and it didn't arc anymore.

I'm guessing that means that the Filter Choke may be bad? How hard is it to replace those and how expensive are they to buy? Also how necessary is it to have that filter choke in the circuit? Can the set be ran without it in circuit?

[Tube TV]

Don't worry about replacing the choke until you know it's bad.
Heres how to test it.

There' a black wire that is connected to the filter choke that leads to the lower end of the terminal strip where the electrlyics are connected.
I can't see the other wire that come from the choke, but it too should be at the terminal strip. Mark these so that you can connect them back in the same places.
Unsolder these wires and and see if you can get any resistance between it and the chassis.
The reading with both wires off the choke should be infinity or at least in the several megohm range between the chassis and one of the choke leads
The reading between the 2 leads off the choke should be low. Somewhere around 3 to 20 ohms for example.

[vortalexfan]

Originally Posted by Kevin Kuehn

OK, so you switched it around. Have you powered up the set with the white wire connected back to pin 2 of the 5U4 since you switched it? If you previously had that white wire going to the negative side of the C1A, & B caps, that alone explains why the set was drawing excessive current, because that point connects to the center tap of the high voltage windings.

I did try it out with the wires switched and it still arced, but not nearly as bad as it did and the tube wasn't trying to red plate either like it was before I switched the wires.
Basically its doing the same thing it did before I replaced the power supply caps.

[vortalexfan]

Originally Posted by Tube TV

Don't worry about replacing the choke until you know it's bad.
Heres how to test it.

There' a black wire that is connected to the filter choke that leads to the lower end of the terminal strip where the electrlyics are connected.
I can't see the other wire that come from the choke, but it too should be at the terminal strip. Mark these so that you can connect them back in the same places.
Unsolder these wires and and see if you can get any resistance between it and the chassis.
The reading with both wires off the choke should be infinity or at least in the several megohm range between the chassis and one of the choke leads
The reading between the 2 leads off the choke should be low. Somewhere around 3 to 20 ohms for example.

OK thanks, I was just getting ready to do that.

[Kevin Kuehn]

Originally Posted by vortalexfan

I did try it out with the wires switched and it still arced, but not nearly as bad as it did and the tube wasn't trying to red plate either like it was before I switched the wires.
Basically its doing the same thing it did before I replaced the power supply caps.

Then by all means do as Electronic M suggested and check resistance from each lead of L1 to chassis ground. You may need to disconnect both L1 wires from the circuit to get an accurate reading.(as Tube TV said above my post)

[vortalexfan]

Originally Posted by Kevin Kuehn

Then by all means do as Electronic M suggested and check resistance from each lead of L1 to chassis ground. You may need to disconnect both L1 wires from the circuit to get an accurate reading.(as Tube TV said above my post)

I checked the filter choke with my ESR/LCR Meter (which also checks resistors and resistance loads) and the filter choke checks out within tolerance of the original specs given in the Sam's Folder, it checked at 27.7 Ohms and 1.69 Henries, which the original specs given in the Sam's Folder for the Choke is 32 Ohms and 1.5 Henries.

As for the individual leads checked to ground, one lead read 254 Ohms and the other lead measured infinite.

[Tom9589]

The filter choke is definitely necessary for proper power supply operation. It’s easy to install - there are only two leads. The bigger problem would be finding a replacement.

[Kevin Kuehn]

Originally Posted by vortalexfan

I checked the filter choke with my ESR/LCR Meter (which also checks resistors and resistance loads) and the filter choke checks out within tolerance of the original specs given in the Sam's Folder, it checked at 27.7 Ohms and 1.69 Henries, which the original specs given in the Sam's Folder for the Choke is 32 Ohms and 1.5 Henries.

As for the individual leads checked to ground, one lead read 254 Ohms and the other lead measured infinite.

[Edit] I'm not sure how it can measure 27.7 ohms across the two leads and be infinite from one lead to ground. But it's bad none the less.

[vortalexfan]

Originally Posted by Kevin Kuehn

Not sure how one lead could measure infinite to ground if as you say you measured 27.7 ohms between the two leads. It should show leakage from either lead to ground, one being 27.7 higher that the other. Make sense?

Well I just tried measuring the individual leads again and now both of them are measuring infinite to ground, which I'm not sure how that's possible, as you said. But of course I'm not sure if I had all that good of a connection between the multimeter probe and the wire coming out of the choke which when you have your multimeter on your workbench top and the choke wire is hanging in mid air its kind of hard to get a solid connection without using aligator clip leads, which I have but not for my multimeter.

[Electronic M]

Originally Posted by vortalexfan

I checked the filter choke with my ESR/LCR Meter (which also checks resistors and resistance loads) and the filter choke checks out within tolerance of the original specs given in the Sam's Folder, it checked at 27.7 Ohms and 1.69 Henries, which the original specs given in the Sam's Folder for the Choke is 32 Ohms and 1.5 Henries.

As for the individual leads checked to ground, one lead read 254 Ohms and the other lead measured infinite.

That 254 ohms from one lead to ground reading indicates a short to ground in L1 ( I assume you unsoldered L1s leads from the rest of the circuit)...........
.... however I'm suspicious of that readinds accuracy.
If you measured from 1 lead to another and got 32ohms, then measured 1 lead to ground and got 254ohms to ground then logic says the other lead should have in the neighborhood of 222 to 286 ohms to ground instead of open circuit that you measured(that or the 32 Ohms across the leads is actually open circuit)....

L1 probably is bad but I'd like you to redo all the measurements on it you just made to confirm no mistakes were made, and hopefully this time not obtain numbers that together should be impossible for this part.

Edit:I see progress was made while I was typing.
Do you you have alligator clip leads with an alligator clip on each end of the wire? If so clip one end to a probe on your meter and the other to the test point in circuit. You can do that for both meter leads to do hands free measurement. This may add as much as an ohm to a measurement, but in most tube circuit work that is too small a difference to matter.

[vortalexfan]

Originally Posted by Electronic M

That 254 ohms from one lead to ground reading indicates a short to ground in L1 ( I assume you unsoldered L1s leads from the rest of the circuit)...........
.... however I'm suspicious of that readinds accuracy.
If you measured from 1 lead to another and got 32ohms, then measured 1 lead to ground and got 254ohms to ground then logic says the other lead should have in the neighborhood of 222 to 286 ohms to ground instead of open circuit that you measured(that or the 32 Ohms across the leads is actually open circuit)....

L1 probably is bad but I'd like you to redo all the measurements on it you just made to confirm no mistakes were made, and hopefully this time not obtain numbers that together should be impossible for this part.

Edit:I see progress was made while I was typing.
Do you you have alligator clip leads with an alligator clip on each end of the wire? If so clip one end to a probe on your meter and the other to the test point in circuit. You can do that for both meter leads to do hands free measurement. This may add as much as an ohm to a measurement, but in most tube circuit work that is too small a difference to matter.

No I don't unfortunatly do not have double sided aligator clips.

The aligator clip leads are on my ESR/LSR Meter leads, which I did try to use as stand alone aligator clips to clip onto the filter choke lead on one end and then take the other aligator clip lead and clipped it to the multimeter probe and the banana plug end of the aligator clip lead that was attached to the filter choke lead and I was still getting an infinite reading (O. L.) on my multimeter for both choke leads, so it seems that the filter choke is bad.

[Tube TV]

Also wiggle the wires on L1 while rechecking for the short to ground to rule out a possible intermitent short . To be at infinity on one side of the choke is not possible.
The choke is simply one long run of wire on a transformer core.
Edit: also make sure that when testing one lead on L1 that the other lead is not touching the chassis or other parts in the circuit.