Foreplay II - tube issue

[Psimon]

Another of my vintage Bottlehead units, my Foreplay II amp.

I was trying to eliminate some hum today and to help me trace the source I swapped the left & right the tubes on the Foreplay. The source of the hum turned out to be something else. However I noticed that the Foreplay had suddenly become extremely microphonic. The tubes rang, dinged if I gently tapped the top, if I touched any metal part there was sizzle of squeaky noise from the speakers even if the volume was at zero.

I swapped them back and the noise has gone, back to normal. However, the right channel has been slightly lower volume for awhile. I had presumed it was my phono stage tubes. But having recently put in a new solid state phono stage, the problem persists. Could it be time for new tubes in the Foreplay? The unit has been running at least 15 hours a week for over 20 years.

Any thoughts? Does it sound like an aging tube of could it be something else? Any recommendation on buy new tubes?

The current tubes are 5965s. I guess a like for like replacement is easiest.


Thanks
Simon

[pboser]

I calculate your tubes have about 15000 hours on them, which sounds like a lot, but what do I know - I'll let experts weigh in on that.  (This source brags about a 10000 hour life: https://www.tubesandmore.com/products/5965-dual-triode)  It won't cost too much to try a new pair of these.
P.S.  Didn't the Foreplay II originally use 12AU7 tubes and their variants? Isn't the 5965 a 12AV7 variant?  Did you make changes to use the different tubes?

[Paul Birkeland]

I wouldn't absolutely say that your tubes are worn out, but it's certainly worth throwing in a new pair to see.  You may also have oxidized pins and pulling and reinserting each tube a few times may clean that off.

-PB

[Psimon]

The guy who built my amp used various mods to the design including transformer, tubes etc. These are the original tubes he fitted over 20 years ago. I'm certain the amp will have been built around using these tubes. He told me it was the best sounding Bottlehead combo he'd made.

I'll try and clean up the pins and see if it makes a difference. But I've found plenty of these 5965s going cheaply on line so I may as well change them.

Thanks,
Simon

[Doc B.]

Put in 5963s instead of 5965s That's what it was designed for and the gain will be much more manageable.

[Psimon]

I'm pretty certain the builder modded the design to match 5965s. If i switched to 5963s would I have to start switching resistors and capacitors?

[Paul Birkeland]

I'm pretty certain the builder modded the design to match 5965s. If i switched to 5963s would I have to start switching resistors and capacitors?

Did the builder replace the power transformer or add another one?  A pair of 5965s will draw too much heater current for one thing.