1 tube reverb & mosfet

[tubenit]

Guys,   would this work?   Any advantage of doing it this way over the typical one tube 12A_7 type?   Would it give a little more oomph/boing?

Does the 220R or the diode need to be there?

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwj1p5amwp3YAhXjYd8KHUmAAEwQFggsMAA&url=https%3A%2F%2Fwww.vishay.com%2Fdocs%2F91059%2F91059.pdf&usg=AOvVaw100_m9cXFoh9ujk2BDruNT

With respect, Tubenit

[kagliostro]

This way ..... 


May be with the mosfet connected as Source Follower you have the advantage of the stronger current on the signal that drives the tank


but how to connect the transformer ? Only to the source follower, between the mosfet and ground ??


If so you require a transformer with a low primary impedance

The way you planned it I don't know  , OK, it remind a paralleled tube, but really don't know


Franco

[tubenit]

May be with the mosfet connected as Source Follower you have the advantage of the stronger current on the signal that drives the tank

I was pondering that approach also?  But like you, I'm not what reverb tank would be needed then?

With respect, Tubenit

[kagliostro]

The problem isn't in the reverb tank

is in the primary of the reverb transformer

I think you must use a low Z transformer like those who are used to drive lines from a CF

if I remember correctly Richard has build such a circuit with Edcor transformer in a mic octal preamp he build few years ago

No, the preamp I was remembering wasn't Richard's Mic Preamp ( http://www.el34world.com/Forum/index.php?topic=10116.msg94794#msg94794 )

The preamp was this Bass Preamp (from one other guy who also post on the forum)

http://www.frontiernet.net/~jff/SonOfAlembic/SonOfAlembicF2B.html


But those are 15k/600ohm OT, not low primary

Franco

[tubenit]

is in the primary of the reverb transformer

Yes, the transformer not tank.  Thanks!   With respect, Tubenit

[PRR]

> would this work?

The IRF is dead-off, does nothing.

The most common MOSFETs need the Gate +positive+ of the Source. You have it negative by the amount of the tube cathode voltage.

You can throw-out the tube there and re-bias the MOSFET. Slightly complicated.

Source follower is not a great answer. Resistor-loaded amplifier is MUCH less efficient than transformer-coupled. The "low output impedance" is only for small signals; large signal impedance is still V/I and for~~0.1Watt output with ~~300V supply you need a many-K load (a transformer) or a lot of loss (excess heat).

[tubenit]

PRR,

OK, thanks for the response!  I appreciate it.  I'll scrap that idea. 

With respect, Tubenit

[2deaf]

The IRF is dead-off, does nothing.

How about when the input signal gets bigger than 4V_p plus the tube cathode voltage?

- - - - - - -

An IRF820 can easily be convinced to drive a standard Fender transformer.  Attached is an example that uses the source follower phenomenon to create a driver that is incredibly similar to the standard Fender driver.

   

[2deaf]

LND150's can also drive the Fender transformer, but it requires a parallel pair in order to stay in the SOA and to operate without those little heat-sink hats.

[kagliostro]

I don't know if this can be of some help



Franco

[sluckey]

You guys are getting close to inventing a totally solid state guitar amp. I've heard that will be the next great generation of guitar amps. 

[shooter]

I've heard that will be the next great generation of guitar amps. 

 
I just turned down a request to "fix" a dead valvestate, I explained why, customer satisfied, he's now asking questions about tubes

[bnwitt]

I gutted and turned several of those Electar Tube 30 amps into 5E3 amps many years ago.  They looked great but sounded like crapola before the conversion.  After the conversion they sounded fantastic and looked great too.

[kagliostro]

I've find this






https://www.tubecad.com/2015/04/blog0321.htm

Franco