[Harp-L] Re: BR Princeton cap replacement

[Jim Rossen <jimjimdr@xxxxxxxxx>]

Cap type can make a significant difference.
Your amp has three basic types of caps- power supply filter caps,
signal caps, and cathode bypass caps.   Filter caps are electrolytic
caps that operate in the power supply of the amp with conversion of
the wall AC to the high voltage DC (called B+ voltage) the amp needs
for operation.  They are prone to failure with age, and should be
replaced in an amp of this age.  The cap type/mfg is not a significant
determinate of tone but the value will influence tone.   However,
replacement of old caps can lead to an increase in power supply
voltage to the amp because old leaky caps will reduce the voltage.
This can lead to the tone change you describe.

Signal caps are within the music signal path of the amp and cap type
can make a substantial difference in tone. Generally, signal caps do
not need replacement and should not be replaced unless they have
failed, or a specific change in cap value is desired.   Vintage caps
may be highly prized.   One occasionally hears stories of dishonest
techs stripping an amp of valuable vintage caps and replacing them
with current production caps, with the intent of selling the former at
a premium.   Different mfg of caps of the same value will sound
different, and there is great variety of opinion about which is best
for a particular amp and purpose.  There can be a 20x difference in
cost of signal caps.   I have been pretty happy with relatively
inexpensive Mallory 150 and Sozo caps for harmonica.

Cathode bypass caps are electrolytic caps that are also signal caps,
but also deteriorate with age.   Replacement is often recommended in
amps of this age.  The mfg seems less important or unimportant for
these.

Jim R


On Aug 23, 8:08 am, "Jon Clark" <jdcl...@xxxxxxxxxxx> wrote:
> I have a 1964 BF Princeton, no reverb. I recently had the caps changed by a local technician.  It seems that the sound is a little tighter or "cleaner" that it was with the original caps. Might be my imagination though. My question is whether different types of caps make a difference in the sound and if so, what cap recommendations are there for a harp application of this amp.  
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