Voltage Readings - DYNACO ST-70 Assembly Manual

* Note # 1 – Make sure you have your meter set to AC or DC as mentioned below. Ground is
any point on the chassis frame. Place the black or negative probe on the chassis and the red
or positive probe on the point mentioned. All tubes should be plugged in, inputs shorted or
connected to your preamp, speakers connected and no signal should be running through the
amplifier. Be careful not to cross two pins with the positive probe !
* Note # 2 – Readings very slightly above or very slightly below the range are not normally
a sign of a problem. Line voltages vary slightly throughout the country. Differences in the
GZ34 rectifier tube can cause variations also. The use of a solid state rectifier in place of the
GZ34 may cause some voltages to be higher.
GZ34 – Pin 2 to ground – 410 - 450 volts DC
Pin 8 to ground – 410 - 450 volts DC
Pin 4 to ground – 330 - 370 volts AC
Pin 6 to ground – 330 - 370 volts AC
Any EL34 – Pin 1 to ground – approx .400 volts DC (depends on bias setting)
Across pins 2 and 7 – 5.9 – 6.5 volts AC
Pin 3 to ground – 400 - 430 volts DC
Pin 4 to ground – 400 - 430 volts DC (2 or 3 volts higher than pin 3)
Pin 5 to ground – minus 30 to minus 38 volts DC
Pin 6 to ground – minus 30 to minus 38 volts DC
Pin 8 to ground – approx .400 volts DC (depends on bias setting)
Quad cap – Section # 1 (square symbol) –----- 410 – 440 volts DC
Section # 2 (half circle symbol) ---------- 400 – 430 volts DC
Section # 3 (NO symbol) ------------------- 400 – 430 volts DC
Section # 4 (triangle symbol) ------------ 380 – 420 volts DC
Central 12AT7 – Pin 1 or pin 6 to ground > 130 – 160 volts DC
Two outer 12AT7's – Pin 1 or pin 6 to ground > 240 – 280 volts DC
Any 12AT7 – across the two incoming heater wires > 5.9 - 6.5 volts AC
"-50 VAC" on driver board > 48 – 55 volts AC
"B+" on driver board > 380 – 420 volts D

Voltage readings

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