I've seen cases of the horiz. being miles off-frequency, but never saw (or heard of) it causing the fly to put out 'too much' juice. The HV is not the product of the sweep frequency but of the fast "fly-back" spike of the sawtooth.

Just wondering if maybe the second 1X2 could be bad. This'd be one case where it would be handy to have a SS stick rectifier to sub in there. oc

Where might one procure such a thing?
The new 1X2B that I have was brand new in the box for whatever that's worth. I'll see if some one else I know has a known good 1X2 to test with.

Have you checked the 1X2's filament for continuity? Here's the data page with basing diagram..
http://www.nj7p.org/Tube4.php?tube=1x2

Filament has continuity.
After much thought I decided that this latest problem happened after I changed 10 tubes and 4 caps. I thought I would take a closer look at the items I replaced before the problem. Following the schematic to each cap I replaced led me to C62. C62 is connected to pin 3 on V17 and ground according to the schematic (as far as I can tell). Can some one confirm this? On the set it is connected to pin 3 and pin 7 on V17. I know I replaced lead for lead of the old cap and can still see a small amount of the lead of the old cap to confirm this. The old cap was one of the black beauties I mentioned that I missed before. I tested pin 7 and it is not connected to ground. Maybe I'm following some one else's botched repair? Or maybe I'm just misreading the schematic?
One other question. The schematic shows pin 7 and pin 8 of V17 connected to "Y" and "Z." There are some other connections on the schematic labeled as such. What does Y and Z refer to?

"X" and "Y" are probably tube heater windings on the power transformer, look around the power supply on your schematic, and you will probably find what they are connected to.

Tom C.

Yes, there is a separate filament supply (Y and Z) for the damper tube and kinescope (the other tube filaments are supplied by connecting to the X supply and ground):

http://antiqueradio.org/art/temp/Majestic1600PS.jpg

I think I read somewhere that a damper is given a separate filament supply to reduce the risk of heater-to-cathode shorts, when its cathode is at hundreds of volts above ground.

The schematic seems to show that C62 connects to ground in some models and to the +255vdc source in other models:

http://antiqueradio.org/art/temp/Majestic1600Damper.jpg

A note elsewhere says, "Dotted in parts are not used in all models. When dotted in parts are used, points marked X are broken." In other words, that leg of C62 would connect either to +255vdc or to ground, depending on model.

Referring back to the first picture, the +255vdc source is separate, not the same as the Y filament source that connects to pin 7 of the damper. So, if I follow this correctly, connecting C62 between pins 3 and 7 is not right for either model.

Here is a bigger chunk of the schematic showing other dotted-in stuff:

http://antiqueradio.org/art/temp/Majestic1600.jpg

There you see that C61 is like C62, connecting either to +255vdc or to ground, depending on model. Parts R95, R97, and C71 are also dotted. Perhaps if you check how all those components are connected in your set (and whether R97 and C71 are even present), that will give a clue how to connect C62.

Phil Nelson

Thanx for chiming in there, Phil. I had formulated a post saying essentially the same thing, but you beat me to it.:D

One thing's still puzzling- he says C62 was connected to pin 7 of the 6W4. That would put it from cathode (pin 3) to heater (pin 7), which would make no sense...

unless....

...the floating heater is clamped to the 255V supply via pin 7.

Otherwise, C62 has gotta go either to ground or to the 255V supply depending on model.

oc

I keep checking this topic to see- "is this the post to say he got it working?"

I've been on the edge of my seat... Great work so far, can't wait to see a picture on it :)

's what I love about AK - the restoration projects here aren't just one person's work - everyone takes part and can't wait to hear of or see the end result when it works.

Occupational hazard too - this feeling is contagious...

Fingers crossed- we've got the champagne sitting ready :D

Dug out this Zenith { Chassis14Z33 } from the B@W room and connected the HV probe to the to the anode of the CRT. I picked this set because it has a vary stable tube horizontal oscillator/output circuit and a coil for the horizontal hold control. Turned on the set and let it warm up, With a normal picture the HV reads 19kv on the probe. Then I turned the horizontal coil one and a half turns counter clockwise. The picture went out of sync and the HV went up to 22 KV. What else was interesting is when I turned the coil one more rotation counter clockwise the HV went back down to 19KV and the picture was a horizontal mess. This proves that there is a direct connection between the horizontal oscillator and the high voltage. I guess I just do not know how to explain the problem properly. All I know is I have seen this type of problem before in the 1950"s set's and they are hard to track down. Also the horizontal circuits are not as stable in a 50's set as the horizontal circuit in a 1969 zenith.
I am not a big fan on installing solid state diodes in place of a diode tube. I tried it once with a ctc 15 chassis damper tube and it increased the horizontal output tube current. Plus it looks funny on the chassis.
Ed

That's an interesting observation, Ed. To tell the truth, I had never tested the correlation between sweep frequency and HV level. But it stands to reason that changing the sweep freq also changes the duration of the retrace/'fly-back' spike from which the HV is derived via resonance (or near resonance) with the secondary winding (the 'tire').
But as you demonstrated, there's only a moderate peak as you tune through it, not a continuous ascent.

Re. the SS stick, I was referring to the HV rectifier type, not a damper. Replaced enough of those in CTC-22s. Gaak.:eek: oc

Quick question to all of you. Are there any tubes that if removed from the set would do damage to the set if it's fired up without them?

Oh yes indeed. The horiz. oscillator. If for any reason the H.output tube loses drive, it loses the negative bias voltage* on the control grid (G1). The plate current goes through the roof and if there were no fuse the output tube could be destroyed in short order, possibly cooking the fly also. That's why there's usually a fuse there for protection.

Removing either of the vertical tubes would kill vertical sweep, which could burn a line across the screen if allowed to run that way. oc

*This voltage is developed by the G1-cathode diode action rectifying the drive signal.

The reason I asked is I thought I would check back through the tubes to make sure I didn't mix some of them up when I reinstalled all of them. I noticed two things. V10 is a 6AT6 on the schematic and I have a 6AV6 installed. I mentioned this before and was told it was ok but thought I would mention it again. V15 (the horizontal output) on the schematic is a 6AV5GT and I have a 6AV6GA installed. Are these interchangeable or is this no good? Also I replaced C40 with a .022mf cap because that is what the capacitor list called for, but the alternate schematic (which is actually what I have) calls for a .002. Is .022 too much for a replacement? If the horizontal tube isn't the whole problem in a nutshell (I'm sure it's not, that would be too easy), I think I'll look back through the set and make sure I didn't replace other caps with the wrong capacitance because of the parts list being different from my set.

The 6AV6 and 6AT6 have identical specifications and pinouts.

A quick google shows me that the filament pins for these two tubes are not the same, so immediately I would say they are NOT compatible. It also looks as if one is a 7-pin tube and the other an 8-pin tube.

Can you trace the 6.3v filament line to the pins on the socket? The place they come out should indicate which tube is correct.

6AV6 specs - Filament pins 3 & 4
6AV5 pinout - Filament pins 2 & 7

Sorry I made a mistake. I have a 6AV5GA installed not a 6AV6GA. My mistake VintagePC.

Ah, that makes a little more sense :) No worries.

Per RETMA designation, they should be compatible - the original GT suffix just means glass tube, whereas the GA suffix suggests glass tube (G) and a revised version that's backward compatible (A).

What's funny is I read the Wiki pages for RETMA and RMA tube designation just for kicks once... now I keep finding myself back on them :)

OK, maybe I found it! I was looking over C61 and C62 again to make sure they are installed correctly. C62 is indeed connected to +255v so all ok there. However, I am 99.9% sure C61 is MISSING! I will be especially sure this is the case if some one can speculate that a missing C61 would cause my glowing V18 problem.

This is also further reinforced by the fact that I had a cap with same value as C61 left over when I did the original recapping.

That could well do it!

Considering C61 is part of what comes out of the 1x2 cap -> through a transformer.

That means without C61, your flyback won't operate properly.

I'd connect it in the same way as C62 - using the optional 255V connection.

I would say the optional 255V connection is the way to go. Every thing else I've seen on the schematics have been in the optional dotted line configuration. I'll give the set a second and third look over to make triple sure that it is not in place and if it's not we'll see how it goes.

If C61 was indeed missing, it'll be interesting to see what happens when he replaces it, since it is the bypass/'filter' for the bootstrapped (B boost) voltage. Since the vertical oscillator is supplied from B boost, the absence of C61 was probably introducing some wonkiness into the vertical waveform too.

What still puzzles me is- he was drawing a healthy 'air arc' off the plate connector of the 1X2. Assuming the replacement 1X2 is good, there should definitely be adequate HV coming out of it.. assuming there is no short to ground. One remaining possibility is that the second 1X2 is gassy. So one question- is the 1X2 getting hot after a few minutes of running? If it's hot, like too hot to touch, it would indicate the tube's gassy (even though it might still test good on a tester).

I've only had the set on for seconds after noticing the problem so I don't know if the 1X2 is hot to the touch. I could test this theory if you think it's ok to leave the set powered up for that long.

It should be all right, (and I'm sure you know this) but don't run it unattended. (and replace C61 before you do fire it up!)

I like to run things through a power bar so I have a kill switch on hand that's not near/on the set, just in case. Then, keep watching and listening for any funny business and kill it if anything else starts acting weird. Keep a good eye on the flyback and kill the power if it starts to drip wax!

I should add that gassy tubes usually have a blue-violet flickering glow to them, which is in the _space_ inside the tube... What it looks like you have (and you can confirm this, since cameras don't usually do fluorescent colours justice) is a pure, deep blue coming from the inner layer of glass itself- that's entirely the fluorescent emission of the glass from being bombarded with high-energy electrons.

There's a couple of videos on YouTube (heh) if you search "gassy tubes" that will help you distinguish between the two.

Umm.. considering the rarity and irreplacibility of that flyback, and since you haven't already run it for more than a few seconds in the fault state, please hold off on this test.
Rather (after replacing C61), do the 'air arc' test again. It will confirm whether the fly's putting out without loading it down.

Now, if the fly's putting out, install the 1X2 with the plate cap connected, and remove the doorknob. This will avoid loading the flyback (in case the tube is gassy). If the tube is good, the HV should come up and light the CRT. If the 1X2 is gassy, it may fry the 470K resistor (R89) in series with the HV lead. R89 is thus "sacrificial" and takes the load otherwise borne by the flyback with a gassy 1X2. Much easier to replace a resistor than the flyback.

Yah, some tubes can glow pure blue and work fine. I have observed this in a couple of sets.

Purple, not so good. The photo shows a 5U4G rectifier in my RCA T-100 just before it failed completely. Definitely purple rather than blue. There was nothing wrong with the TV, that old tube just gave up the ghost.

Phil Nelson

http://antiqueradio.org/art/temp/Fried5U4G.jpg

I guess .1% wins this time. I found C61. It is a .05 instead of a .035 though. It was one of the black beauties and didn't have it's rating on it. It had the same marking bands as two other black beauties that were .05 though.

A few youtube searches on gassy tubes and I think this is what I have. The last two posts came in after I did the test so didn't have a chance to read the "don't do that" warning. The set was still only on for less than a minute.
http://www.flickr.com/photos/23097242@N03/5873904324/
This will help make it a little easier to see what the tube is doing. The video is of the new tube. The old tube does close to the same thing, just not nearly as much blue glow. I suppose #3 could be the charm.

Are you still hearing the hissing or spitting sound? A length of plastic tube held to your ear can help you pinpoint its location.

Phil Nelson

I am hearing a sparking noise, but I think it's coming from the 1X2 itself. You can see in the video that it is sparking on the inside. This is also what the old tube did.

Killer suggestion on the length of tube though. I will definitely remember that for the future.

If the doorknob isn't causing the arcing, it could be the socket itself. Have you checked it yet? Carbon tracking on HV parts can cause shorts from seemingly nowhere, so make sure you inspect the rectifier tube socket and replace it if you're in any doubt.

Interesting thought. I'll inspect.

Damn, that thing is TOASTY!


http://www.youtube.com/watch?v=x7KK7bXJV2c

Tried this and it's not the problem.

Ok tests ran, here are the results. Fly is air arcing away. Door knob removed and HV going right to the picture tube. I want to rewind a bit to before. Miniman82 first suggested removing the doorknob cap and firing the set up to see if that solved the problem. The doorknob cap is secured to the base of the rectifier through a screw in the base to the top of the cap. On my first test I removed the screw. On this test I removed the screw and MADE SURE that the base was not in contact with the cap at all. Different result. The tube did not glow or crackle at all this time. Unfortunately a new arc has developed. It is between the flyback and the filament winding for the rectifier. I've indicated where it is with the white arrows below. It is not constant, and only happened 8 or so times total with all the tests I have done tonight. It seems that Miniman82 might have put his money in the right place and the doorknob is toast. It is not shorted to ground but it could be toast. A new doorknob might be the answer. I don't know what to do about the sparking flyback though.

http://farm4.static.flickr.com/3016/...a8bbe8cc94.jpg

Most people here will coat the flyback with a "sensor-safe" silicone product (regular silicone produces ammonia or acetic acid as it cures, which corrodes copper). That will likely kill the arcing. A few wraps of PVC electrical tape might work in a pinch for testing until you can get the right stuff.

At this point, I'd recomment replacing the filament winding for the rectifier and the doorknob cap. I often find filament windings have degraded insulation, and that's never a good thing around HV.

Got a good supplier for a 500pf 20,000v door knob capacitor?

Digi-key has a few... for example:
http://search.digikey.com/scripts/Dk...me=445-3890-ND
http://search.digikey.com/scripts/Dk...me=445-2235-ND


... but they won't be cheap :S

Well sunnava gun, so it was the doorknob all along, and now the filament winding is popping through. Some kind soul oughta send him a hunk of HV wire to replace that with, along with a doorknob.

So as I sit here and ponder I can't help but think that the door knob cap ISN'T shorted to ground. If that cap was shorted to ground it would certainly account for our problem, but could just a leaky cap cause our problem? If not could it be the ground side of the cap some how isn't grounded? Or some other problem other than the cap itself being bad. I just know that some times in my work when I think I've found the answer from trouble shooting I just end up "fixing" things that aren't broken and still not finding the real problem.

OK, did the CRT light up with a raster after you removed the doorknob? If so, it would pretty well prove the doorknob was at fault. Probably arcing internally since it measured open circuit on your ohms test.

Earlier you mentioned a "new arc" that's developed. I (probably erroneously) interpreted it to mean there's a hole in the insulation of the filament winding that's allowing a DC arc. That would be evinced by a loud, sharp snapping sound. If instead the "arc" is a bluish, lightly hissing corona discharge from the 'tire' to the filament loop, you may be able to insulate it with some silicone. Is it possible to move the filament loop further down on the frame, away from the 'tire'?