mixed mode class A amp - e.g., anode and cathode outputs with gain.

[DummyLoad]

fiddling with a mixed mode AF amp. this was taken from the fender vibroking, a design by bruce zinkey. the plan provides 2 outputs with a moderate amount of gain. the cathode output is in phase with the input and the anode output is out of phase with the input as we'd expect with a RC coupled grounded cathode amp. this one has a twist: both outputs have gain.
 
some observations:
works really well. impressed with the headroom. i used the values used in an original vibroking amp except for the anode (inverting out) coupling cap.

i grafted this input stage to the 6L6GC practice amp i posted recently out of convenience and because i wanted to hear what is sounded like. schematic attached with telemetry.

AV on the cathode (non-inverting out) is about 10. AV on the anode (inverting out) is about 24. Ibias is about 1.9mA with values indicated with ~280V B+. 

in the pics in the link below:
1) input signal from low distortion osc. is ~1KHz @ ~100mV pk.
2) in pic 1 the lower trace is the input signal - Ch.1 set to 100mV (probe 1X). upper trace is cathode out - Ch.2 is set to 1V/div. (probe 1X) sweep at .5ms. trigger source Ch. 1. notice that both channel traces are in phase.   
3) in pic 2 the lower trace is the input signal - Ch.1 set to 100mV (probe 1X). upper trace is anode out - Ch.2 is set to 2V/div. (probe 1X) - notice signal is hotter than cathode output and out of phase, as we would expect with a grounded cathode class-A amp.

https://www.dropbox.com/sh/haoolp69r5nowxs/AADGC6NzlEnTmTMTV258aBhMa?dl=0

--pete 

[SILVERGUN]

I have some interest in this because I've had a Vibroking build idea in the holster for quite some time now.


Looking at the schematic it appears that the signal off of the cathode would have a path to ground.
What am I missing? 

[DummyLoad]

I have some interest in this because I've had a Vibroking build idea in the holster for quite some time now.


Looking at the schematic it appears that the signal off of the cathode would have a path to ground.
What am I missing? 

it's a 270K load resistor: random value pulled out of the breadboard resistor tray. it's simply simulating a load. ;-) 


--pete

[SILVERGUN]

it's simply simulating a load. ;-) 
--pete

Ahhhh….I see, said the blind man

[DummyLoad]

it's simply simulating a load. ;-) 
--pete

Ahhhh….I see, said the blind man

... as he picked up the hammer and saw.


--pete