Mighty Monarch of The Air

[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

[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

[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?

[Electronic M]

One thing to check on the no video issue, is the detector diode(if it is not a tube). The SS diodes sometimes fail.

[roundscreen]

I am glad to see you have a full raster on your set and now you can run the set to fix the other problems. What I would do first is hook up a signal source to the set, Give the tuner a good cleaning. Check all the tubes in the if section and clean all the pins on the tubes in the if. Does the brightness and contrast controls make any changes in the raster? If they do, The video may be getting to the crt. Try turning the horizontal hold control in both directions and see what changes that makes in the raster. I am sure you do not want to hear this, But go through and re check your work. Ask any one here and they will tell you the same thing. We ALL make mistakes and need to check over what we have done. Do it ten times if ya have to. Also make sure you take a rest from the set. Pick at the set a little at a time. You will be surprised at the ideas that will come to mind when you are rested and take your time at it.
Ed

[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.

[roundscreen]

oc explains it better

[jeyurkon]

There seems to be a design error here. The Sam's doesn't show what the HV is, but a 16GP4 typical operating voltage is 12KV. If they were actually operating it at 12KV, the Peak Inverse Voltage that the HV rectifier would see is slightly less than twice this. A little under 24KV.

The 1X2 is rated at 15KV PIV. So, it would break down. They're probably running the 16GP4 at 10KV or less, maybe 9.5KV. That would still cause the 1X2 to break down.

The 1X2-A, and 1X2-B are rated at 20KV PIV, the 1X2-C is rated at 22KV PIV.

If you can find a 1X2-A,B, or C then it would probably work without the modifications you made.

John

[old_coot88]

Dang, this puppy's got some interesting early circuit topologies. The CRT is driven with video at the grid instead of the cathode, and brightness control is done via the cathode, the reverse of later standardization. And AGC is via a simple detector-driven, non-delayed type just like the AVC (automatic volume control) circuit in AM radios. And the damper is placed differently in the flyback's DC path than in later standardization, wherein B+ is supplied directly at the damper's plate.

Interesting study in the evolution of TV design.

[old_coot88]

Originally Posted by jeyurkon

There seems to be a design error here. The Sam's doesn't show what the HV is, but a 16GP4 typical operating voltage is 12KV. If they were actually operating it at 12KV, the Peak Inverse Voltage that the HV rectifier would see is slightly less than twice this. A little under 24KV.

The 1X2 is rated at 15KV PIV. So, it would break down. They're probably running the 16GP4 at 10KV or less, maybe 9.5KV. That would still cause the 1X2 to break down.

The 1X2-A, and 1X2-B are rated at 20KV PIV, the 1X2-C is rated at 22KV PIV.

If you can find a 1X2-A,B, or C then it would probably work without the modifications you made.

John

Just a little ditty for the "outside the box thinking" department , i wonder if at some point the flyback could've been replaced with one putting out higher HV, intended to drive a larger CRT.

[jeyurkon]

Originally Posted by old_coot88

Just a little ditty for the "outside the box thinking" department , i wonder if at some point the flyback could've been replaced with one putting out higher HV, intended to drive a larger CRT.

And even if they didn't replace it with a higher HV flyback, it looks like the original design was on the ragged edge.

[old_coot88]

Wonder how difficult it would be to convert it to a 1B3. Or better yet, for ease of conversion, a SS stick rectifier. Does anybody know where those can be obtained nowadays, other than out of a junked BW set of 1970s-'80s vintage? One fella on here converted an old BW Admiral, using a HV stick from a Quasar color set.

[jeyurkon]

I think the main difficulty would be putting in an Octal socket to replace the Noval socket. I suppose one could make a socket adapter without too much trouble.