Shielded mains cables are used in Industrial and hospital environments to prevent interference from mains into the equipment. These equipment usually measure in micro volts of some thing and very suseptable to mains noise. The screen does not help if teh grounding is noisy. They also use clean earth which is separate from electrical earth.
These equipment also have line filters to filter wide band noise.

The skin effect always exists, but very very negligible at mains frequencey. The higher frequency you go, the current at the center compared to the outer conductor goes towards zero. The dead area also increase with frequency. This increases the effective ac resistance (impedance) of the cable. In practice, they use tubular conductors for high frequency or use litz wire for smallar currents- many fine strands of thin wire insulated from each to improve effective current.

There is no need for these cables in guitar amps, unless it is a marketting hype.
Good grounding methods are just what is required.


regards,
mandu

'I ruled out the speaker.  The buzz is present within the note, but isn't there when there is no signal'

Did you try with another speaker? All speakers are quite when there is no drive.

regards,
Mandu

Thank you all for so many guide lines. About 12 years before I have built 20+20 watts class A amp with sucess. For the heat sink I used a VSD chassis. That time I did not have the guitar to test. I gave it as a present to one of my friends. I believe that design was from Elector magazine, with two 2n3055 at the output with upper transistor acting as a current source.
I am looking into a good heatsink now, I may go with a fan cooling if I get a smaller one. This will be all descrete amp. Since mechanical construction is a pain, I believe could be done in a months time. This will be a amp head only, difficult as a combo.

For the preamp, I would like to use all FET preamp.
Thank you all once again.

Thanks for the feedback.
I am not aware of any branded class A amp in the market, but looking into building a 30 - 40 watts amp (pushpull, with output transformer)
I play cleanonly.
regards,
mandu

Could also be
the output stage bias current is a bit low due a component problem.
This buzz usually disappear at higher volumes and returns when the sound is about to die.
OR
the speaker is rubbing on the cone.
You can try with another speaker if possible

regards,
mandu

I never had a chance to use a class A solidstate amp with guitar.
Anybody has experience trying a guitar with such an amp?

Thanks in advance.
Mandu