70s Twin Reverb - Unusual noise

[falconer333]

Hi all,
I've just joined as I have too many amps and most they have some form of issue! My current disappointment is a 70s Twin reverb that I had professionally serviced and fully re-tubed a little over a year ago. It's been kept in the same place since I got it back, played a handful of times and over-wise flight cased. Turning it on today, (for the first time today in around 6 months), it is suddenly producing this strange continuous noise (not a typical hum) a couple seconds after flicking the standby switch. (See video clip below)

Any opinions on what could be causing this would be greatly appreciated.
Thanks,
Jonathan

[Kaaskop]

I don’t know enough to weigh in based on the sound clip by this might be a starting point.

https://robrobinette.com/Tube_Guitar_Amp_Troubleshooting.htm

[Latole]

Did the noise stop with volume at 0 ?

It could (not sure) be from defective filter caps.
Have they been replaced?

First I would clean all the lamp sockets.
A tube amp that has not been used for a long time can produce oxidation on the sockets

Unplug and plug tubes few times may do the job