Re: set-up tuning

[Barry C Schaede <barrys@xxxxxxxxxxxxxxxxxxx>]

Fender amplifiers do not have what is commonly referred to as vibrato.  
They amplitude modulate.  They used two basic circuits for this 
modulation.  The first is a tube oscillator circuit that varies the bias 
to the output tubes this was used on the early Concerts and Supers along 
with the Bandmaster 3-10 and the Princeton's.  I also think the Pro and 
Tremolux used the same circuit.  The second more common Blackface circuit 
uses an opto coupler device with a neon bulb that's flashed on and off by 
an oscillator circuit this in turn is coupled with a light dependent 
resistor that goes off and on to the beat of the flashing light turning 
the output tubes on and off.  FJM