Mighty Monarch of The Air

[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.

[vts1134]

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.

[old_coot88]

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.

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).

[vts1134]

Originally Posted by old_coot88

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.