Mighty Monarch of The Air

[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?

[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?

[vts1134]

Originally Posted by earlyfilm

How did you measure the coil?

I measured it's DC resistance, 35ohms.

[old_coot88]

From the "thought i'd seen it all" department, this has gotta be the first problem I've ever seen caused by the HV being too high in a BW set. Color sets, yes. But never a BW before this one.
Anyhow, if adjusting the horiz. drive hasn't reduced the HV sufficiently, it's easy to cut back the gain of the output tube itself (the 6AV5). One method is to put a resistor in series with the cathode (say 100 ohms as a ballpark starting value). The other is to reduce the screen grid voltage (on pin 8). This is the method I would try first. Assuming you don't have a resistor decade box or a resistor assortment on hand, go to RadioShack (ugh ) and get a card of 2.2K half-watt resistors. Locate the 5.6K screen grid resistor R84. Open one leg and insert a 2.2K resistor in series with it. Bring the set up and see what the HV reads. This will give you a ballpark indication of which way to go with R84, ie., whether it needs more resistance or less. If it needs more, add another 2.2K in series. If that's too much, you can make a 1.1K by paralleling a couple of the 2.2K.
The caveat is, if you succeed in getting the HV down and the arcing cured with the set at full line voltage, the width may be reduced too much. I'm betting the width will still be sufficient. If it's not, then a new plan of attack is in order. oc

[vts1134]

Originally Posted by old_coot88

From the "thought i'd seen it all" department, this has gotta be the first problem I've ever seen caused by the HV being too high in a BW set. Color sets, yes. But never a BW before this one.
Anyhow, if adjusting the horiz. drive hasn't reduced the HV sufficiently, it's easy to cut back the gain of the output tube itself (the 6AV5). One method is to put a resistor in series with the cathode (say 100 ohms as a ballpark starting value). The other is to reduce the screen grid voltage (on pin 8). This is the method I would try first. Assuming you don't have a resistor decade box or a resistor assortment on hand, go to RadioShack (ugh ) and get a card of 2.2K half-watt resistors. Locate the 5.6K screen grid resistor R84. Open one leg and insert a 2.2K resistor in series with it. Bring the set up and see what the HV reads. This will give you a ballpark indication of which way to go with R84, ie., whether it needs more resistance or less. If it needs more, add another 2.2K in series. If that's too much, you can make a 1.1K by paralleling a couple of the 2.2K.
The caveat is, if you succeed in getting the HV down and the arcing cured with the set at full line voltage, the width may be reduced too much. I'm betting the width will still be sufficient. If it's not, then a new plan of attack is in order. oc

Decided to go with Bill's suggestion on this one. I stopped at my local antique electronic shop (sorry just couldn't bring myself to go to Radio Shack) and get myself a handful of resistors. After two hours of shooting the breeze with Don, which if you know Don is a very short conversation, I headed home ready to tackle the task at hand. It took two 2.2k resistors in series with R84 to bring the anode voltage down to the point where the 1X2 stops experiencing high voltage failure. At full line voltage the anode is still way over spec at 16kv, or at least that's what my meter and high voltage probe reads. There is no sign of high voltage problems any more, no sparking 1X2, no corona discharge around components in the hv cage, no black vertical lines on the screen. Tonight I go to sleep for the first time with a full screen raster . Granted there is no video, the horizontal isn't linear, and the screen is full of retrace lines but I'm pretty happy to be at this point .

Just some questions/concerns at the end here.
Horizontal size and Horizontal linearity control slugs do nothing to the screen when adjusted.
Can some one tell me what Horizontal Drive and Horizontal AFC are/do?

[old_coot88]

Well son of a gun. Fancy that. First of all, is your set the version with the 'color converter socket' and "color switch" (M7)? If so, clean the heck outa that switch with contact cleaner since it's in the video signal path and could be killing the video if it's dirty.**
Also if the set has a phono input and a TV-phono switch (M6), good idea to clean that switch too while you got the squirt can going.

Originally Posted by vts1134

Can some one tell me what Horizontal Drive and Horizontal AFC are/do?

Drive adjustment is supposed to vary the amplitude of the signal going to the 6AV5's control grid.
AFC= automatic frequency control. One section of the 6SN7 (V15) serves the AFC function while the other section is the oscillator.

**Just like the 'service switch' in color sets. Ask Phil about that.

[old_coot88]

Originally Posted by vts1134

...I stopped at my local antique electronic shop (sorry just couldn't bring myself to go to Radio Shack) and get myself a handful of resistors.

While i share your disgustipation with RS on several levels, in many places they remain the only walk-in source of small parts like resistors, caps, fuses etc. ever since local parts houses went the way of the dodo bird. I grudgingly have to patronize RS pretty regularly. oc