Set Bias Current Acoustic Amp TDS420 ACC 260 261 Tremolo Q3 500mvpp 1k Hertz Heathkit Sig-Gen DSO150

Setting the Tremolo Circuit bias current on the Acoustic Control Corp 261 Amp involves sending a one kilo-hertz signal into the input jack. Sampling the input signal level at the emitter of transistor Q3 to make sure it reads 500 mili-volts peak to peak, sign wave. After that ground oscilloscope probe to chassis then test the signal at Base of Q4 to see if the level requires adjustment, the adjustment involves setting the signal level to be pretty much the same as Q3e output, half a volt peak-to-peak.
The adjustment is made via R67 on the underside of the Reverb Tremolo Board on. This 1970s amp may have bad variable resistors that make setting the bias difficult.
Tools Used:
Insulated philips screw driver from automotive electronics kit.
Techtronix TDS420 scope
DSO150 pocket scope
GE Isolation Transformer
Killowatt AC current meter
5AMP Variac
Heathkit IG-82 Signal Generator, any input device that can play a tone can be used, like tone app and cell phone, etc.