Re: Type CA module in a 545

Tom Lee

Sorry to be late to the party, but first, congratulations on getting it to work.

If you ever intend to revisit the repair, I’d suggest measuring the filament voltages, just to be sure that something global wasn’t causing the tubes to run on the cold side, as the marginality you’re seeing is somewhat surprising. It is of course possible that you have a group of tubes that have aged similarly ungracefully, but I’d look at other possibilities too.

— Cheers,

Sent from my iThing, so please forgive typos and brevity.

On Jun 26, 2021, at 12:53 PM, David Kuhn <> wrote:

No, no, no, sorry, the 6AU6 tubes.

I fixed the problem. I cheated. I kept going back and forth between the
"good" and "Weak" module. The differences were so subtle. I do think I
have a few weak 6AU5 tubes, but I can not prove that to myself anymore.
Anyway, I cheated and turned the gain of the 545A chassis up (R1027) up a
bit. Now all modules can be calibrated for proper gain.

On Sat, Jun 26, 2021 at 3:42 PM Jeff Dutky <> wrote:

Where are you seeing CA plug-ins for $10 (much less 99 cents) on eBay? All
I see are $39 + $9.99 shipping.

Not that I need another CA, but at those prices I might have a need for a
parts mule or three.

-- Jeff Dutky

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