Collins 390 (non A) audio problem

[iw5ci]

I noticed that my 390 receiver has maybe some capacitor issue in the audio board (i suppose).
Unnoticeable while connected to an antenna, when the receiver is disconnected from the ant, i ear some (frrr frr frrrrr i cannot really write the sound  ) from the speaker not continously but randomly present.
If i pickup the audio from the diode output, the problem is not there.
So it's probably a condenser leaking in the audio amplifier stage.
I have never dismantled a 390 and i need some help of the best and unpainful way to reach the audio amp ad check condensers on it.

thank you.

[w3jn]

It's easy.  Just turn the receiver over, and find the green Philips screws holding the audio/regulator chassis in.  Disconnect the wiring harness and it'll come right out.

This could be a filter capacitor problem, causing the voltage regulators (6082 tubes, a pair) to oscillate.  Then again, could be anything.