Hello Tom!
On 03 Feb 98, Tom Scioscia wrote to Rich Lockyer:
 RL>> in the preamp with shielded cable, with one end of the shields all
 RL>> tied to one ground point.
 TS>        Exactly what does parasitic oscillation sound like?
Kinda like a reverb feeding back, but at a relatively low volume level.  It 
gets worse as you increase the volume.  Tom's Traynor was fine here, but when 
I took it to him and we turned it up from "condo-volume" to "house-volume", 
it started doing it.  It didn't start immediately, rather, right after I hit 
a chord.  It almost sounded like a microphonic tube, and was 100% 
high-frequency stuff.  My solution was to replace the wires that I made 
longer with shielded cable.  Fender's solution was to hang small caps 
everywhere to bleed the HF off before it hit the grids of the output tubes.
 TS>        But with true GAS, do you know what you're spending until it's 
oo
 TS> late?
Sure... and in advanced cases, you explain to the wife that list price could 
have bought FOUR of what you just bought.
 TS> My dad-in-law just spent a grand on a Peavey 412MS and two Peavey PA
 TS> cabs and then wondered why. :)
Nope... not true G.A.S.  A true G.A.S. sufferer has no remorse after getting 
home.
 RL>> You checked the plate voltage on the Marshall?
 TS>        No, but I assumed that if they got up that high, the higher gain
 TS> Marshalls were probably being hit with that much.
Probably not.  Output wattage is a function of plate voltage, the impedance 
of the output tubes, transformer, the number of output tubes, and of course, 
the level of the signal hitting the grids.  IF an EL34 has the same impedance 
as a 6L6 (it's gotta be reasonably close because Carvin allows you to use 
either with a simple flip of a bias switch), then the plate voltage would be 
comparable in any 100 watt amp.
 TS> This was a JCM 900. I
 TS> couldn't get any output distortion out of it at all. I had to crank the
 TS> output on my processor to get any sweetness out of the amp.
You couldn't get a JCM900 to distort on 10?  Something was wrong with it... 
that's one of the highest gain amps available.
 TS>        Well, I know I like the sound of the 30 year old RCAs in there. 
)
 TS> I'd like to see what unused ones sound like. :)
Like I said... give Jim at AES a call.  He's got plenty of NOS tubes at 
reasonable prices.
C-ya! Rich
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