SuperTriode with BJT and MosFet - a good idea?

[KlausB]

Here are the driver and the power supply.

 

[stocktrader200]

works fantastic, I built a amp using MJE13007 transistors and 6922 twin triode.
no feedback pure triode power. 25 w with 165v B+ and 3k transformer.
simply hang the transistor off the cathode and bias with 1N4148 plus 1.5k resistor

 

[KlausB]

Hi stocktrader,

that sounds great. Do you have a schematic?

Regards

KlausB

 

[stocktrader200]

Klaus, I started a thread on it a while back.

http://www.diyaudio.com/forums/tubes-valves/268043-3-x-3-tube-amp-30-watts.html

 

[KlausB]

Congratulation, this is truly a neat Project. I also prefer BJTs over MosFets. Their main problem is secondary breakdown at higher voltages + biasing class A. That is why i have to use a MosFet as the cascoding transistor.

 

[KlausB]

The two power supplies of the single ended hybrids are already assembled and contain a lot of Swedish iron. When I switched it on the first time I was seriously impressed for it was deas quite, no hum, no vibration, just plain quite with all voltages standing. I also was surprised that the simulations matched the real life voltages and currents within the limits of the component tolerances. LT spice is truly a great help.

 

[stocktrader200]

BJT 's are more linear in the on range and have lower c-b capacitances so are better for VAS stages. Mosfets however are much better power switching devices as they don't latch up and have a softer turn on / off characteristic.
I set the 3 * 3 amp so that the BJT's are always on.
I used them here as the BJT will draw current from the 6922 respective of load
The 12AX7 rolls off from miller effect well before the 6922 & MJE13007 setup

 

[KlausB]

My finalized single-ended hybrid project can be found here:

http://www.diyaudio.com/forums/tubes-valves/71300-photo-gallery-792.html#post5082409

Regards
KlausB