Mighty Monarch of The Air

[vts1134]

Originally Posted by old_coot88

Vts1334,
As was suggested back in posts 210 and 214, what you describe sounds more like something under the 1X2, not the tube itself, is doing the arcing/sparking.. like maybe a leakage path from the socket to ground.

As a test of this theory, if it's possible to temporarily 'float' the socket by removing whatever it's mounted to, that would eliminate a leakage path as the problem.
oc

I did this. The socket was only connected to the tube and the lead to the picture tube. I still had the same problem. The sparking is definitely coming from inside the tube itself. The problem I had below/around the tube was corona discharge from various locations, the "tire," the filament loop, the connection to the wire lead to the picture tube, etc...
Wouldn't it make sense that if those components are driven past their voltage limits that they would begin to show corona discharge?

Originally Posted by old_coot88

It seems very doubtful that three 1X2s are all gonna be displaying an acring/sparking problem such as you describe, even with the driving voltage being a little over spec. The tubes should have enough 'headroom' to be able to handle it without a problem.

How much head room do you think they have? With the input voltage at 90v y and z are already at 270vdc. At input voltage of 95v and the anode voltage reading 14kv (the limit according to the 16gp4 spec) there is no problem in the high voltage area. Above 95v input, when y and z get up over 310v then SPARK! I haven't measured anode voltage when the 1X2 is at it's fail point but I suspect it's a good deal over 14kv.

[old_coot88]

Originally Posted by vts1134

I did this. The socket was only connected to the tube and the lead to the picture tube. I still had the same problem.

Ok, my bad. I didn't realize you'd already done this.

The sparking is definitely coming from inside the tube itself. The problem I had below/around the tube was corona discharge from various locations, the "tire," the filament loop, the connection to the wire lead to the picture tube, etc...
Wouldn't it make sense that if those components are driven past their voltage limits that they would begin to show corona discharge?

Yes, now that you've done the 'float' test.

With the input voltage at 90v y and z are already at 270vdc. At input voltage of 95v and the anode voltage reading 14kv (the limit according to the 16gp4 spec) there is no problem in the high voltage area. Above 95v input, when y and z get up over 310v then SPARK!

I don't have access to the LV supply section of the schematic. But the most relevant voltage is where the flyback system itself is supplied. That would be at lug# 6 of the flyback. The print calls for 210V. If that voltage is signifigantly over spec, it could sure as heck be overdriving the whole flyback system.

The schematic shows 255V at other locations in the chassis. Is that voltage over spec too? If it is, it would suggest the LV power supply is putting out too much juice. Is there any evidence of the power transformer having been replaced?

Or if the 255V source is not over spec, could there be a miswire somewhere that's putting 255V onto the 210V line?

Maybe Phil could post the print showing the LV section.

One thing's for sure- we all gotta admire the heck outa your tenacity in rassling this critter. For a total Noob, it's truly been a baptizm of fire. When you get it whipped, you can rightly call yourself The Dragonslayer.

[jeyurkon]

If the focus coil were open or disconnected maybe the +255 would be too high.

Anyhow, here's the power supply section.

John

[old_coot88]

Originally Posted by jeyurkon

Anyhow, here's the power supply section.

John

Aha. Thanks John. One piccy's worth a thousand words. I think i forgot that Phil did post that earlier. Geezerly brain fade.

So vts1134, what is the actual voltage at the input side of the choke (L1)? What is the voltage on the downstream side of L1, where the focus coil connects? Is it signifigantly over the specified 255V?

What is the voltage at the downstream side of the focus coil, where it connects with filter C2D? Is it signifigantly above the specified 210V?


Forget 'Y' and 'Z'. That's just the 'floating' heater supply for the damper and not relevant to the problem at hand.

[old_coot88]

Just a little FWIW regarding the damper's floating heater winding. Since there is a high level pulse of a few thousand volts on the cathode, there's potential for heater-cathode arcing (a very common problem with damper tubes). By allowing the heater to float (rather than being clamped to ground like the rest of the heaters), the effective pulse level between heater/cathode is reduced, thereby reducing arcing potential.

Most sets don't use a dedicated supply to float the damper's heater. In fact this feature is found only in a few old high quality sets.

[vts1134]

Originally Posted by old_coot88

One thing's for sure- we all gotta admire the heck outa your tenacity in rassling this critter. For a total Noob, it's truly been a baptizm of fire. When you get it whipped, you can rightly call yourself The Dragonslayer.

Ha, just wait. This is only the latest problem, I haven't told you that I still don't have a picture yet. It might be a while until this is over. I know I've said it before but I can't thank you all enough for teaching me what I know refer to as my crack addiction. I can't wait until I can show you a picture on this bad boy, take a 5-7 minute break to admire it, and start the next one .

[vts1134]

Originally Posted by jeyurkon

If the focus coil were open or disconnected maybe the +255 would be too high.
John

The focus coil is right on spec.

[vts1134]

Originally Posted by old_coot88

Aha. Thanks John. One piccy's worth a thousand words. I think i forgot that Phil did post that earlier. Geezerly brain fade.

So vts1134, what is the actual voltage at the input side of the choke (L1)? What is the voltage on the downstream side of L1, where the focus coil connects? Is it signifigantly over the specified 255V?

What is the voltage at the downstream side of the focus coil, where it connects with filter C2D? Is it signifigantly above the specified 210V?


Forget 'Y' and 'Z'. That's just the 'floating' heater supply for the damper and not relevant to the problem at hand.

I've found that all of the above locations are above spec voltage, but not so much as to be a problem.
I'm going to continue to look for out of spec voltages. 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, but could this cause an over voltage situation on the fly? The schematic gives it two Majestic part numbers, they are B-1.533-1 and B-1.532-1. Does any know what these part numbers would correlate to on a replacement part?

[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 vts1134

The reason I ask is that my horizontal size control is at 3 ohms and spins, but does not adjust in impedance. Obviously broken, but could this cause an over voltage situation on the fly? The schematic gives it two Majestic part numbers, they are B-1.533-1 and B-1.532-1. Does any know what these part numbers would correlate to on a replacement part?

I'm sorry this was a mistake. I'd edit my post but I think it's been up a bit too long. The coil is right on 35 ohms. Should it change impedance when it is adjusted though?

[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.

[old_coot88]

Originally Posted by vts1134

I'm sorry this was a mistake. I'd edit my post but I think it's been up a bit too long. The coil is right on 35 ohms. Should it change impedance when it is adjusted though?

You're reading DC resistance, and it will not change with the slug adjustment. The impedance (AC resistance) will change with the adjustment when there is an AC waveform across the coil.

[earlyfilm]

Originally Posted by vts1134

The coil is right on 35 ohms. Should it change impedance when it is adjusted though?

Yes, it would if you measured it correctly.

If you measured it with an ohm meter, it would not change the value.

Confused?

Lets start this topic over again:

>>> 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 . . . . . <<<

>>>Originally Posted by earlyfilm
Are you confusing impedance with resistance? If not, how are you checking inductance?<<<

>>> Originally Posted by vts1134
I'm not sure what you mean here, so I probably am.<<<

OK, let me ask a similar question in plain language.

If you have a coil of wire and measured the resistance and you and got, say 35 ohms.

You then measured the resistance with a powdered iron core inside it, the coil would still get 35 ohms.

You then measured it with your finger stuck through it, it still would read 35 ohms.

Why, because your VOM / VTVM measures your coil using simple direct current.

Do you agree?

Now, impedance is just the alternating current measurement of inductance with a few capacitor variables thrown in for good measure.

Inductance measures alternating current resistance, in this case, a very high audio frequency of just over 15,000 cycles per second (or Hertz.)

When the powdered iron core is inserted, the alternating current resistance (inductance) increases, but the direct current resistance remains the same.

Now about sticking your finger in the coil, is unknown, but it probably would raise the inductance, but not as much as the powdered iron core. However, depending on voltage involved, I must might not wish to test it that way. :-)

On the other hand, if you stick a brass rod in, it will lower the impedance (but not below it's direct current value).

OK, now your horizontal coil ain't nothing more than a coil of wire with an adjustable powdered iron core inside, and a capacitor connected over part of it or in resonance with it.

If you measured the horizontal coil with an ohm meter, just like my example, it too would not change.

How did you measure the coil?