hybrid output

jfetter

Member
2012-06-25 12:57 pm
na

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needtubes

Member
2003-05-24 9:23 pm
I have done something similar in my most recent headphone amp using the 6418 and ZVP3306 with a ZVN3306 sitting on top as a mu follower (discovered the circuit myself somewhat by accident last fall, though its topology was probably known before). It simulates very well with these parts, but I've not successfully generalized it with other combinations of tubes and MOSFETs. Seems some playing with settings is required to get it to settle down. At any rate, the amp works great with the 6418 and 3306's, and I just posted pictures today of my completed build.

Is that your circuit, or did you find it in a reference book? I've been wondering where to look to determine if I had reinvented the wheel...
 
I've had success using something like this for the input section of a SET power amp. My breadboard version uses a 6J6 twin-triode diff amp, an NPN constant current load for the PNP gain stage, then a BJT Sziklai pair buffer driving the power tube in class A2. I don't use the diode. Distortion at closed-loop gain of 100+ and 90Vpp output is below the FFT mud in a good Tek scope, so better than 50dB down.
 

jfetter

Member
2012-06-25 12:57 pm
na
use a horizontal output BJT on the low side and connect the collector to the plate , base to cathode 10 ohm emitter resistor and adjust setup for proper operating current.
this way a cheap $4 transistor has 1500v blocking ability.
6922 works fantastically in similar setup


i want to double check i picturing correct. can you sketch it out?
thanks
 
He's talking about the triodington configuration, used to make a small signal triode appear as a power tube. Unfortunately, those high voltage transistors generally only have a beta of about 10 and small signal gain of a little less. The configuration works well when using the standard output transformer configuration, but I take it your looking for a direct drive type of circuit.