Replacement tubes for a Sonny Jr

I have a Sonny Jr 2.  Actually, I have two of them!  (One, virtually unused,
might be for sale, but I digress.)

One of the points emphasized in the promotional material for the amps (both
SJ1 and SJ2) was their self-biasing feature.  You can switch out rectifier
and power tubes without rebiasing, as the amp is self-biasing by design.

Barbecue Bob is right: pre-amp tubes are self-biasing.  This does not depend
on the design of the amplifier.  Even in a fixed-bias amp, you can switch
out pre-amp tubes for other tubes, even tubes with very different gain
factors, without rebiasing.

According to my understanding, it is always best to check the bias on a
fixed-bias amp when you change **either** power tubes or a tube rectifier,
and adjust the bias if necessary.  I do not know how to do this.  I bring my
one fixed-bias amp (tweed Harvard, 5F10 circuit, the smallest fixed-bias amp
Fender ever made) to a trusted tech when I change power tubes or the
rectifier.  You may get away without doing this, or you may not.  As Mr.
Eastwood put it, "Are you feeling lucky today?"

Again, this is unnecessary in the case of the Sonny Jr.s

Gary Onofrio (Sonny Jr.) is really good about supporting his amps.  You can
email him at:



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