ASKAMPMAN
Peavey Problems
Hi Jeff,
I’ve had a Peavey Classic 30 for about
seven years. For what I do, I like it a lot.
At first it had an indescribable response
and tone which I could not believe for the
price. However, in the last year I’ve started
having some problems. The overdrive channel is more distorted and muddy sounding,
although the clean channel sounds great
and remains the same even when overdrive channel acts up.
better or worse than another, they just sound
different. Some have slightly more gain than
others. Some distort differently than others.
Each has its own tonality. The same holds
true for EL84s. Not only do different manufacturers’ EL84s sound different, but the bias
current will differ under identical operating
conditions. This can lead to an amp that
sounds cleaner or possibly even dirtier that it
did with the previous set of tubes.
tubes went “bad, with no life or light burning,” as well as another incident where two
of the EL84 output tubes “went bad at the
same time.” This leads me to believe that
there are at least two different intermittent
failures in the filament supply circuit and that
the tube company was probably correct in
telling you that the tubes probably didn’t all
go bad at once. Let me explain.
The tubes also need changing more
often. It has four EL84s and three
12AX7s, and I
use matched sets whenever possible
from a reputable tube company – whose
name I won’t mention but wouldn’t
believe me when two EL84s went bad at
the same time. 12AX7s go bad quickly,
usually one at a time, but at one point
all three of my 12AX7s were “bad,” with
no life or light burning. This happens
after two to three weeks on the road,
playing about 2/3 of the nights.
This particular amp has a very atypical filament arrangement. The fact is that there
are actually two distinct sources of filament power, one for the preamp tubes and
another for the output tubes. In addition to
that, the filaments of the preamp tubes, as
well as the filaments of output tubes, are
wired in series. This is akin to the old style
strings of Christmas lights where one goes
out, and they all go out. A failure anywhere
in their respective filament circuits – even an
intermittent solder connection on one pin
of one tube socket – can affect the entire
string of tubes.
Before this I spent hours a day jamming
louder and harder at home and didn’t
change a tube for years. Maybe it’s my
ears or my taste is changing. What’s your
perspective?
Thanks!
Will
Hi Will,
After reading your question, it’s my opinion
that there are a few different issues here
to be dealt with, so let’s take them one at
a time.
In other words, replacing the 12AX7s and
EL84s with different type tubes can absolutely cause you to wind up with an amp that
sounds and feels markedly different. One
thing you do need to bear in mind is that
today’s tubes, at least in my opinion, seem
to go microphonic more quickly than tubes
made back in the heyday of the ‘60s and
‘70s. This is especially true in a combo situation where the tubes are subjected to the full
vibration being generated by the speaker(s).
One more aspect of this failure to consider
is that these intermittent conditions may be
preventing the tubes from getting a consistent filament voltage and current. If that
is the case, the operation of the tubes will
suffer, and a tube that is not heated properly
will not function properly and therefore will
not sound the same. Have your technician
thoroughly go through the filament circuits,
including the solder connections on the 5-
watt resistors associated with the tube filament supplies, and you should have a much
more reliable amp.
First, you mention that the overdrive channel
is more distorted and muddy sounding than
it used to be. One cause of this could be as
simple as tubes. I know that you’ve replaced
the tubes, so they obviously can’t be old and
worn out, but what did you replace them
with? If they were not the same tubes that
were originally installed in the amp, then
chances are the amp is going to sound different. A Chinese 12AX7 sounds different
than a Russian 12AX7, which sounds different
than another 12AX7. Not that one sounds
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Another possible cause of your amp sounding more distorted and muddy might be
speaker fatigue. While your amp is not terribly old (assuming you purchased it new),
the speaker(s) could be sounding old and
tired. Even though you perceive the amp to
be sounding good in the “clean” channel,
speakers respond differently at lower cleaner
volumes than they do at louder more distorted conditions.
Here’s hoping you get that “Classic” tone back.
Jeff Bober
Co-Founder and Senior Design Engineer
Budda Amplification
jeffb@budda.com or www.budda.com
©2007 Jeff Bober
Now on to something that I believe is actually a problem with your amp. You mentioned
that at one point three of the 12AX7 preamp
