18 watt tremolo starts. Then slowly loses intensity and stops

[Fiat_cc]

As the title says. Trem was working fine, and has been for some time. Now it starts, but slowly (over 30 seconds or so) loses intensity and stops. I’ve tried replacing the tube with another, and no noticeable improvement. I know this circuit can be finicky, and sensitive to tubes, but it’s frustrating me as it has been fine for months.

[Williamblake]

What plate voltage do you have? I am using the  18w tremolo and it stopaped working when the rectifier died. And did you tweak the oscillation  loop?

[Fiat_cc]

What plate voltage do you have? I am using the  18w tremolo and it stopaped working when the rectifier died. And did you tweak the oscillation  loop?

Can’t remember plate voltage on that tube now. It’s been ages! Around 180 on the oscillator and 125 on the gain stage from memory, but I’ve built a few amps since then, so could be mis-remembering.
Yes, I used the well know tweaks and updates available at 18watt.com. It has been really well behaved up until now. My voltages are definitely higher than usual because I’ve put the 18 watt preamp in front of a Super Reverb output section, so the B+ starts much higher. Obviously I’ve used dropping resistors to get in the ball park, but yeah, suddenly the trem is misbehaving. It had been on for quite some time, so I wonder if heat related maybe.

[sluckey]

Get a handful of tubes and start rolling 'til you find (hopefully) a happy one.

[Fiat_cc]

Get a handful of tubes and start rolling 'til you find (hopefully) a happy one.

So they really are just that finicky on tubes?
My next version I plan on using the Fender VibroChamp tremolo circuit.  Same overall effect, being preamp bias wiggle, but hopefully more reliable.