SS buffer on a tube preamp and clean channel question

[dschwartz]

Hi all, i´m designing a tube preamp pedal, based on the dual rectifier preamp..

the thing is, i don´t want to use 3 tubes (the mesa preamp uses 5 triode stages), so i want to know if i can replace the last stage (the buffer) with a solid state buffer..

what would work best? mosfet? fet? silicon? opamp?
in case i chose fet/mosfet buffer..should i lower the drain voltage to what?

other question..
i need a clean channel out of it..i was thinking bout taking the signal out of one stage and drive a different tone stack..
wich stage do you recommend me to take the signal from?

at last.. the power supply..will a 7812 regulator be enough for two tube heaters? and for the SS buffer..should i make a 24v regulated output too?

warm regards to all!!!!

[petemoore]

  I was reading hifiguys using Mosfet as near drop in replacement for a 12ax7 stage and liking it.
  Don't remember every detail, but do remember it was supposedly quite easy to do, and the results were 'boutaz good to preferrable.
   As far as the regulators, I'd look at the tube data sheet and see what current it uses, use that to calculate for the number of heaters, compare to the regulator[s max current.
 

[snoof]

looks like at 12v, it's 150ma per triode.

[CraigR]

Daniel

Read this - http://www.geofex.com/Article_Folders/mosfet_folly/mosfetfolly.htm    It is the article in cited earlier about swapping MosFets for triode stages as cathode followers.

I hope you are planning to run the tube stages off higher voltages (>140VDC).  12A_7's run off low voltages sound lousy IMO.

[dschwartz]

HA HA..i was just reading that article!! well, the question bout replacing the buffer is answered then!!

i´m planning to use 300VDC or so!!

it seems that a 7812 will do the job.,.. it stands 1amp.. and 4 triodes are 600mA..so..i´ll use it ..well colled obviously..

but the question bout the clean channel.. can i use a part of the signal chain as a clean channel?