[TenTec] Argosy 525 keying problem

[SSmith9831@aol.com]

Hi-

Purchased an Argosy 525 at a local hamfest this weekend but found it might
have a problem.

When I key the rig I hear a thumping sound that accompanies the sidetone.  It is very noticeable when wearing headphones like it is overdriving the phones
but I dont think that is the problem. When the drive knob is turned down to zero the thumping disappears or is very muted and it increases in volume as
the drive knob is advanced.

I am thinking that it is one of the switching transistors or FETs thats gone bad. 

Anyone have any thoughts as to what components I might check or possible solutions?

Also the sidetone is sort of hard sounding and I remember someone mentioning in an earlier posting that some of the early Ten Tecs generated a square wave
sidtone.  Is there a modification out there to smooth or soften the sidetone? 

Thanks

Steve
KI0MZ
Castle Rock,CO