Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: tubenit on September 08, 2011, 07:00:01 am

Title: Timbo's tubes and mosfets
Post by: tubenit on September 08, 2011, 07:00:01 am

I saw that Timbo had posted this under solid state but since it's definitely amp designing and using tubes in the circuitry, I wanted to reference what he shared here so others would be sure to see it.  He shares how to use mosfets to add reverb and vibrato to a tube amp.  That could be useful if there is limited space.

http://www.el34world.com/Forum/index.php?topic=12259.new#new (http://www.el34world.com/Forum/index.php?topic=12259.new#new)

With respect, tubenit

Title: Re: Timbo's tubes and mosfets
Post by: TIMBO on September 08, 2011, 02:26:58 pm

Hi guys, Here's the link where i found it (interesting amp) was also hoping to find a mosfet active loop but so far nothing (maybe they don't work that way  :think1:)I had thoughts that this loop circuit could be a good candidate because when turned on (with nothing plugged in)it only slightly adds gain  :dontknow: Hope the more SS savvy can help.Thanks

http://www.blueguitar.org/new/articles/other/mikede30.pdf (http://www.blueguitar.org/new/articles/other/mikede30.pdf)

Title: Re: Timbo's tubes and mosfets
Post by: Fresh_Start on September 09, 2011, 10:31:53 am

TIMBO - thanks for that link!  Interesting circuit.  I hadn't thought of injecting tremolo that way for a cathode biased amp.  Any downside that you know of?

Cheers,

Chip

Title: Re: Timbo's tubes and mosfets
Post by: tubeswell on September 09, 2011, 11:49:16 am

Quote from: TIMBO on September 08, 2011, 02:26:58 pm

Hi guys, Here's the link where i found it (interesting amp) was also hoping to find a mosfet active loop but so far nothing (maybe they don't work that way  :think1:)I had thoughts that this loop circuit could be a good candidate because when turned on (with nothing plugged in)it only slightly adds gain  :dontknow: Hope the more SS savvy can help.Thanks

http://www.blueguitar.org/new/articles/other/mikede30.pdf (http://www.blueguitar.org/new/articles/other/mikede30.pdf)

Interesting that he used jfets on the mosfet sources like that. I wonder whether you could get away with just using IRF820s as a straight sub for a triode stage with drain going to (what would otherwise be) the plate connection, gate to the grid connection, and source to the cathode connection. I see he has the gate reverse-biased with a zener and bypass cap and the jfet hooked up (like some kind of voltage regulator?) to give the source voltage the same way you'd get a cathode voltage in a triode stage. Is that just a belt and braces approach? Or is there some other wisdom for that? (I guess I don't really understand SS stuff that well)

Title: Re: Timbo's tubes and mosfets
Post by: Fresh_Start on September 09, 2011, 12:38:32 pm

Google "MOSFET Follies" for R. G. Keen's take on replacing tube triodes with MOSFETs.

HTH

Chip

Title: Re: Timbo's tubes and mosfets
Post by: kagliostro on September 09, 2011, 01:37:13 pm

Many thanks for sharing the link Timbo & Tubenit

Kagliostro