Mighty Monarch of The Air

[old_coot88]

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]

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]

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

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]

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

[VintagePC]

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]

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]

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.