Mighty Monarch of The Air - Page 12 - Videokarma.org TV - Video

Phil Nelson · #**166** 06-22-2011, 11:35 PM

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):

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:

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

old_coot88 · #**167** 06-23-2011, 08:10 AM

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

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

CoogarXR · #**168** 06-23-2011, 03:52 PM

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

VintagePC · #**169** 06-23-2011, 05:59 PM

Quote:

Originally Posted by CoogarXR

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

roundscreen · #**170** 06-24-2011, 06:59 PM

Quote:

Originally Posted by old_coot88

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

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

old_coot88 · #**171** 06-24-2011, 09:39 PM

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.

oc

vts1134 · #**172** 06-25-2011, 02:37 PM

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?

old_coot88 · #**173** 06-25-2011, 03:37 PM

Quote:

Originally Posted by vts1134

...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.

vts1134 · #**174** 06-25-2011, 06:44 PM

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.

VintagePC · #**175** 06-25-2011, 07:03 PM

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

Quote:

Originally Posted by vts1134

...schematic is a 6AV5GT and I have a 6AV6GA installed.

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

vts1134 · #**176** 06-25-2011, 07:17 PM

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

VintagePC · #**177** 06-25-2011, 07:23 PM

Quote:

Originally Posted by vts1134

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

vts1134 · #**178** 06-25-2011, 08:28 PM

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.

VintagePC · #**179** 06-26-2011, 06:39 AM

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.

vts1134 · #**180** 06-26-2011, 07:05 AM

Quote:

Originally Posted by VintagePC

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.