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Author Topic: Afterglow - now I really mean it!  (Read 2030 times)

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Offline pboser

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Re: Afterglow - now I really mean it!
« Reply #30 on: June 05, 2020, 12:02:59 PM »
Yes, that’s right.
Peter Boser

Offline Paul Joppa

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Re: Afterglow - now I really mean it!
« Reply #31 on: June 05, 2020, 12:18:48 PM »
Well, you want 2A3 pins 1 and 4 to be about 200v, pin 3 about 155v. One of the 5965s seems to get you there in either amp - I'll tentatively conclude that the amps are basically wired correctly. The voltage is a little high (220 not 200) but that might go down with some tens of hours burn-in, so I won't suggest optimizing it just yet.

But the seemingly bad 5965 is inconsistent - it works differently in each amp. Could be oxidized tube pins of course. Or a difference in the tube/socket interface, like worn socket contacts, not-quite-straight tube pins, etc. Check to be sure that small movements of the socket contacts can't cause unwanted shorts.
Paul Joppa

Offline Doc B.

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Re: Afterglow - now I really mean it!
« Reply #32 on: June 05, 2020, 12:29:25 PM »
Quote
But the seemingly bad 5965 is inconsistent - it works differently in each amp.

Maybe the two amps are wired to swap triodes, so one amp is uses the left triode for the voltage amp, the other amp uses the right triode.
Dan "Doc B." Schmalle
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Offline pboser

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Re: Afterglow - now I really mean it!
« Reply #33 on: June 05, 2020, 01:06:30 PM »
Hi Doc,
I remember that Buddha suggested that setup for the 5965, but I'm pretty sure the triodes are paralleled.  I checked the assembly manual and it seems I haven't changed that part since the beginning.

PJ,
I took out the small tubes, cleaned the pins with scotchbrite pad, straightened the pins, and looked at the underside of the socket.  I might have had the new cathode resistor too close to the adjacent pin, so I bent it away.  Put the tubes back in where they had been most recently - the second test.  Here's what I got:
220/190
441/450
173/139
220/189

So, on the theory that one of my new NOS tubes may be ng, I dug out another pair of 5965 - not the ones that were originally in it a few weeks ago.  And I got this:
203/207
445/445
159/164
203/207

So that's pretty good, right?   What do you think about the pin 2 readings?
Peter Boser

Offline Paul Joppa

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Re: Afterglow - now I really mean it!
« Reply #34 on: June 05, 2020, 02:04:47 PM »
Pin 2 is just where I hoped it would be  :^)

Those voltages look satisfactory to me. Listen to it for a few weeks to be sure the 5965s have settled into their groove, then re-check the 2A3 voltages - then we can talk about refining the voltages if it seems worthwhile.

I expect it will sound different now ...
Paul Joppa

Offline pboser

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Re: Afterglow - now I really mean it!
« Reply #35 on: June 05, 2020, 02:25:46 PM »
Okay, I'm ready to find out!  Thank you, PJ, PB and Doc!
Peter Boser