I suppose I should have mentioned this but the term Plexi is a pretty
generic term. The one I'm speaking of is the one with the tied
cathodes on the input stages. I also fiddled with the bias
arrangement and reduced things to one cap. Works just fine either
way.

Anybody have any experience with either the Clarostat or Spectrol
multi-turn pots? Dimensionally they're about 1-1/4" with 0.3"
spaced leads. Should beat the hell out of that little bitty thing that's
on the Hoffman board which always made me a little nervous.

Carl Z 

Carl,
I use Clarostat 2 watt sealed plastic conductive pots
exclusively(sometimes Allen Bradley if I can't get the Claros) for
the signal circuits in my amps and usually the same for the bias
control. I have used the multi-turns on a few amps but I find that
the locking 2 watters are nearly as good. I find that the Clarostat
pots are excellent. I also use Clarostat resistors. Of course I use
the cheap CTS carbon pots for repairs if that's what the amp had in
it to begin with.

Peter S 

Better quality resistors like MF and CF
make an amp sound better because you bring the noise floor down. 

For future projects of a similar nature, if you are unable to obtain
the original carbon comp resistors and blue axial poly film and foil
signal caps, here's a solution for obtaining the original tone:

For signal caps, use the SBE orange drop PS series caps (poly film
and foil). Their construction is very similar to the originals and they
are of high quality. For resistors, use modern carbon films, but use
values that are around 10% (or even more, up to 20%) higher than
the those called for by the schematic. Not all of them have to be
this way, but I would at least do this for all plate and cathode
resistors. Most of that "old" tone is due to drifted carbon comp
resistors (which almost always drift UP over time) -- but I strongly
believe it is the actual resistor value, not its construction, that makes
most of the difference (not taking into consideration noise, which is
a lot worse with CC resistors).

   As for the never-ending debate between types of coupling caps,
I recommend the following experiment: for one of the more critical
coupling caps wire up a switch so that you can select between
different types (ceramic, mica, polyester, polypropylene). The
difference can be most noticeable if the signal is very rich with lots
of harmonic content. Or not... if there is a lot of compression and
high freq roll-off after that point in the circuit you might not hear that
much difference. With something like a 470k/470pF RC "couplet"
after a distorted stage I could really hear the difference between a
ceramic and a mica cap- like night and day.

Speed's view of the foodchain (FWIW)
I don't think resistors matter anywhere near as much as caps, 
and caps don't matter anywhere near as much as trannies &
speakers 
and nothing matters as much as tubes. :-) 

Your view of the food chain is 100% dead on IMO. I do the same
thing with regard to caps and function. Resistors too. I only use
WW in the PS and usually CF in the tone chain, although I use
CC's when a customer wants them. I also have a couple of amps
that I built for myself that have CC's in them(Dont ask). I rarely use
MF.

marshall presence cap



Generally speaking, in a given amp, the traditional .1 value will give
you a much more spikey hissy sound when turned up....the .68 will
effectively bypass the feedback circuit and give you gobs and gobs
of incredible output stage distortion, but the bottom will stay
tight(unlike removing the feedback resistor)......a .47 cap will act
alot like the .68 only it will give a bit more(apparent) midband
emphasis. I like the .68 and .47 caps on amps that I normally run
full blast. I often find that the .1 is too shrill.....of course, it depends
mostly on plate voltage...higher voltage amps tend to be brighter.
You can try any value you like here betweeen .068uf and 1uf and
see what you like best. The 1uf will mush the low end at high
volume on most amps....the .047 will shear off the top part of your
head from just below the ears on up.

Peter S