Replace EL34 in the powersection with MOSFET?

[JMFahey]

Long time ago I made a class A+B output stage, bridged, for the BEAG guitar amp with damaged output transformer. The guy wanted it to be repaired overnight, but I did not have an OT, and did not have a chance to rewind one, so I installed instead of it a PS with 50W toroid, and made a SS output stage. It sounded nice, and musicians were impressed that a guitar amp now can play bass. B|

It is not class AB, it is class A+B, you can see what I mean on the graph to the right. Transistors never cut-off, and the amp goes from "triode" to "pentode" mode when overloaded, exactly like output tubes.

Sorry but you are showing that transistors DO go into cutoff for a large part of the cycle (almost 50% of it by the way) , enlarge the image and you'll see they stay at ZERO amperes for a long time.
Depicted as: "0.0A"
Your graph shows (minus) -0.3A as the bottom line, where of course transistors do not reach.

You just set a very high (compared to what's usual) idle current of 300mA so this AB2 power amp stays a little longer in the Class A section, maybe up to a couple watts, but not at full power (or even half ) .

Why you state "from "triode" to "pentode" mode" is beyond me, transistors are 3 legged devices but behave as pentodes all the time.

And power pentodes behave as .... well ..... "pentodes" ... unless wired as triodes which is usually not the case, even less in Guitar amps.

 

[gabdx]

Hello,

I obtained an old amplifier, with transistor preamps and a tube invertor and power amp with EL34.

I am going to use the oputput trafo on a different project.

It seems wasteful to me, to waste a EL34 power amp on an old transistor preamp.

I was thinking would it be possible, to keep the power transformer, throw out the output transformer and build a mosfet power end?

Shcematic here

Thanks

Took a glance at the schematic and it seems there is a phono and tone controls with transistors.

What is wrong with the sound??? It looks a very well made amp!

If you want a clean sound bypass the tone control boards and insert directly the CD player input RCA to the volume pot at the first tube, the impedance sound be ok with a pentode

 

[kacernator]

Long time ago I made a class A+B output stage, bridged, for the BEAG guitar amp with damaged output transformer. The guy wanted it to be repaired overnight, but I did not have an OT, and did not have a chance to rewind one, so I installed instead of it a PS with 50W toroid, and made a SS output stage. It sounded nice, and musicians were impressed that a guitar amp now can play bass. B|

It is not class AB, it is class A+B, you can see what I mean on the graph to the right. Transistors never cut-off, and the amp goes from "triode" to "pentode" mode when overloaded, exactly like output tubes.

Would like to use your circuit as guitar power amplifier. But to get good guitar sound, I need low damping factor. What is the output impedance of your circuit?

Thank you.