Mighty Monarch of The Air

[earlyfilm]

vts1134,

While it is possible that some component in the set has failed, you seem to have followed a logical step-by-step trouble shooting path and you have not located the problem. Let's do a little thinking out side of the box.

1) Is the variac that you are using an old fashion one with an autoformer and a mechanical slider in it?

1a) If yes, have you checked the output voltage with a different volt meter? It is possible that the built-in volt meter is off.

1aa) If yes and the meter is not correctly reading, check the variac wiring to confirm that both the meter and the output are connected to the same output taps because many autoformers have multiple taps and can we wired to either increase or decrease range of the output voltage.

1b) If the variac is a modern solid state unit designed for lamp dimming, then the non-sine wave output will cause a normal AC voltmeter to read incorrectly. (Only an iron vane meter can correctly read the peak-clipped output from one of those.)

2) Does your variac, or your service bench, have a constant-voltage transformer in it?

2a) If yes, then the non-sine wave output of that transformer will cause a normal AC voltmeter to read incorrectly. (Only an iron vane meter can correctly read the peak-clipped output.)

Originally Posted by vts1134

In the meantime my question du jour has to do with L18, the horizontal size control. The schematic calls for an impedance of 35 ohms. It doesn't give it a value range though. Would 35 ohms be on the high side, or low side? The reason I ask is that my horizontal size control is at 3 ohms and spins, but does not adjust in impedance. Obviously broken . . . . .

3) Are you confusing impedance with resistance? If not, how are you checking inductance?

4) As a final suggestion, since Pittsburgh is a large city, see if you can find a volunteer who is familiar with 60 year old electronic circuits to double check both the value and wiring of your replacement capacitors.


It has been my experience that I can almost never find an error that that I made while repairing a circuit.

Please understand, in my 60 year involvement with electronic circuits, I have been tripped up by each of the above mentioned items.

James.

[vts1134]

Originally Posted by earlyfilm

vts1134,

While it is possible that some component in the set has failed, you seem to have followed a logical step-by-step trouble shooting path and you have not located the problem. Let's do a little thinking out side of the box.

My favorite kind of thinking!

Originally Posted by earlyfilm

1) Is the variac that you are using an old fashion one with an autoformer and a mechanical slider in it?

Yes

Originally Posted by earlyfilm

1a) If yes, have you checked the output voltage with a different volt meter? It is possible that the built-in volt meter is off.

I hadn't until just now. It didn't occur to me that the meter could be off. Turns out it was. The built in meter reads low, 95v is actually more like 110v. 120v is more like 140v. Unfortunately with ACTUAL input voltages at line level the spark still happens in the 1X2, but ACTUAL input levels at 115 are ok. The last 10v on the input side are the killer.

Originally Posted by earlyfilm

2) Does your variac, or your service bench, have a constant-voltage transformer in it?

No

Originally Posted by earlyfilm

3) Are you confusing impedance with resistance? If not, how are you checking inductance?

I'm not sure what you mean here, so I probably am.

Originally Posted by earlyfilm

4) As a final suggestion, since Pittsburgh is a large city, see if you can find a volunteer who is familiar with 60 year old electronic circuits to double check both the value and wiring of your replacement capacitors.

It has been my experience that I can almost never find an error that that I made while repairing a circuit.

I do have some one locally that I could take the set to. I'm not sure I'm at that stage yet. If every one here is at that point with me then let me know and I'll cease my daily questions, no hard feelings .

Originally Posted by earlyfilm

Please understand, in my 60 year involvement with electronic circuits, I have been tripped up by each of the above mentioned items.

James.

I still run into things in my job that end up being a forehead slapper after hours of trouble shooting only to realize "press the power button" or any number of other day 1 lessons. It's always, always, always ok to "think outside the box" with me or "talk to my like I'm stupid" because I'll either learn something new or reinforce something I already know, either way I don't take offense.

[old_coot88]

Hey vts1134
Just for the heck of it, what voltage are the heaters getting? It should be a nominal 6.3 VAC (measured from point 'X' to ground). Is it signifigantly higher? Lower?

[vts1134]

Originally Posted by old_coot88

Hey vts1134
Just for the heck of it, what voltage are the heaters getting? It should be a nominal 6.3 VAC (measured from point 'X' to ground). Is it signifigantly higher? Lower?

6.3 pretty much on the nose on all tubes except V17- the damper, V18- the hv rectifier, and V19 the lv rectifier.

[earlyfilm]

I asked if vts1134 had double checked his input voltage:

Originally Posted by vts1134

My favorite kind of thinking!

Yes

I hadn't until just now. It didn't occur to me that the meter could be off. Turns out it was. The built in meter reads low, 95v is actually more like 110v. 120v is more like 140v. Unfortunately with ACTUAL input voltages at line level the spark still happens in the 1X2, but ACTUAL input levels at 115 are ok. The last 10v on the input side are the killer.

Your next step should be to connect your set to a DVD recorder or anything that will give you an analog RF output and bring up your set at lower-normal-voltage and adjust the set to get it working the best you can.

Once all the controls are set correctly, your still slightly too high voltage may correct itself.

Jas.

[old_coot88]

Originally Posted by earlyfilm

Once all the controls are set correctly, your still slightly too high voltage may correct itself.

Jas.

Possibly so. But the option of cutting the gain a bit on the 6AV5 may buy a little more headroom and require less 'brinksmanship'. oc