Fender silver face twin amp sizzling sound

[Jay D]

Hello forum:
I have a Fender silver face twin reverb amp who is experiencing a "sizzling sound" when you try playing a guitar through it.
I have done a complete cap job (filter caps, cathode bypass caps) and New output tubes. Went through each pre-amp and driver tubes replacing with new ones, one at a time, and then each plate resistor checked with an oscilloscope. the problem still exists. Set up a small mic, amp, and headphones, and connected the amp's output to a non-inductive resistive load. I then proceeded to go close to major component on the chassis, played the connected guitar, and when I miked the output transformer, here is where I heard the sizzle sound.

Has anyone experience this problem?

Thanks,

Jay D.

[pdf64]

So this sizzle noise is being made acoustically by the OT in response to signal?
Just to be clear, can it be heard through the speakers? Observed on a scope (of the speaker output, either with real speakers or resistive load)?
Pete

[Jay D]

Hi Pete:
The sizzle noise can be seen and heard with speakers and oscilloscope. The previous stages and power stage look good, 'scope on output - see problem.

Thanks,

Jay D.