Peavey Tube Driver Distorts-Solved!

[CJ]

got a peavey deuce 6l6 100 watt on the bench, sounds distorted,

traced the problem to the transistor driver circuit, 1979 amp, Soundmeyer creation, looks like he was inspired by the musicman transistor driver,

input wave is fine from the opamp preamp section, output signal at collectors is clipped,

 

[CJ]

looks like the transistors are over biased, thus dragging down the collector supply voltage,

voltages comes off main B+ ( 6l6 OPT supply) through a pair of 22k 1 watt to the driver circuit, ollector voltage s/b 145 but is about 22

so i need to trim the bias down to increase transistor resistance to plug voltage drain,

transistors were changed to NEC types which i replaced with some nice RCA's from Tektronix stock, hfe = 50

maybe original 2n3439 had lower gain? these are hi v types, 350 volts,

replaced the lytics.

any ideas? thanks!

 

[CJ]

if you guessed increase emmiter degen resistor, you were right!

4.7K > 6.8 K did the trick.

collectors at 105 which is about as up close and personal i want them to get to 525 vdc.

waveform good, ship it. after i figure out which colored knobs go where.

i bet Peavey gain selected/matched those transistors for the 4.7 K circuit.

still do not know why the + 16 v supply is connected to the base via 10 k.

full schemo>

 

[JohnRoberts]

if you guessed increase emmiter degen resistor, you were right!

4.7K > 6.8 K did the trick.

That isn't emitter degeneration (which would be two resistors, one in series with each emitter) but setting the bias current of the LTP lower which will also shift the dc voltage of the Grid(?) resistors higher. (I am not the tube guy)

JR

collectors at 105 which is about as up close and personal i want them to get to 525 vdc.

waveform good, ship it. after i figure out which colored knobs go where.

i bet Peavey gain selected/matched those transistors for the 4.7 K circuit.

still do not know why the + 16 v supply is connected to the base via 10 k.

full schemo>