On Jan 5, 2024, at 3:45 PM, Steve Wedge, W1ES/4 via <w1es@...> wrote:

I may have found the problems.? Note the use of plural here. I'm going to let it sit for an hour before I declare "Victory!".

I did what I should have initially done when confronted by such a bizarre issue: Shotgun all of the tubes at once and work backwards.? When I "shotgunned" all of the tubes, the problem seems to have gone away.? So far, I am fairly sure that at least three different tubes contributed to this, as Ray Magliozzi used to say, "Woe and Intrigue".

First of all, I discovered that a former owner had put a 6AU6 into V2's position.? Fair enough: it uses the same basing as the 6HS6 but doesn't have nearly the gain and its curve is quite different.? In fact, I have owned so really early stuff (an R-4 and a T-4) that used a 6AU6 at that location.? This seems to have affected the gain but not impacted the AGC.

V3 (12BE6) seems to be a contributor.? These are famous for going gassy and when they do, tube testers don't always find them until they're really bad.? So V3's replacement is staying in.??

V5 (12BA6) looks like it was a contributor.? Again, I had swapped it out by itself and didn't see much of an improvement.

Right now, I've replaced V4 and V9 with the original tubes and V9 pulled things down very quickly V4 was also contributing.

SO Gary, thanks for your suggestion!? I had swapped one tube at a time and kept having trouble.? There were .multiple bad tubes that were contributing but one of the 12BA6's was the worst offender.

Ronnie can finally get his receiver back!

73,

Steve Wedge, W1ES/4

Time flies like an arrow.? Fruit flies like a banana.

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On Friday, January 5th, 2024 at 1:36 PM, Steve Wedge, W1ES/4 via <w1es@...> wrote:

Thanks, Gary.

Yeah, I swapped out tubes already but one at a time.? I have cleaned out the sockets and used a Proxabrush with DeOxIt in all the sockets.

I've changed four more resistors and thought I had a "Eureka!" moment but it didn't happen.

To completely discount the tubes, I think it's now time to replace all of the tubes at once.? I'll let y'all know if that did it.? You're in the right direction and I have had gassy 12BE6's mess things up in the past...

Steve Wedge, W1ES/4

Time flies like an arrow.? Fruit flies like a banana.

Sent with secure email.

On Friday, January 5th, 2024 at 11:23 AM, wb6ogd <garywinblad@...> wrote:

Wow, poor Steve..
Sounds like you have replaced everything, what a tricky one.

The one thing that I know pulls the AVC line is gassy tubes.? I don't know how much the gas changes with warmup, maybe Richard or someone does?

I might try pulling tubes on the AVC bus and watching the AVC lines during warmup where you are seeing the problem.? The voltage won't be right but
just look for drift.
73,
Gary
WB6OGD