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6v6 preamp
6v6 preamp

My next project.

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Hi Guys

Note that diode bias for gain stages is highly restrictive and could be thought of as a form of fixed-bias that is nonadjustable. As TUT described, diode bias also blocks the option for voicing via the cathode.

TUT describes the use of power tubes as preamp gain stages. It is generally low on return for investment, shall we say, but if it provides the character you desire then just do it. The iteration shown here may have a conflict between the fixed cathode potential and the variable screen potential, assuming the pot will be on the panel rather than used as a preset. If it is to be a user control, it would be better to have conventional cathode biasing.

The inductive load will allow for a high output, but power tubes do not have that much voltage gain per se. They are also noisier than preamp tubes. The heater current is quite the penalty, as well. On the other hand, you can drive fairly low load resistances since there is far more cathode current available than any preamp tube could offer.
This not for a guitar amp. Is for computer stereo multimedia amp, to drive the input of Surface Amplifier. Also, my version of a morph control. Surface needed one more gain stage to get the 5 watts per channel, that I was looking for.
Since people here are unfamiliar with a "Suface" amp an explanation of exactly what it is might make your post more interesting. It would also be helpful to understand why you'd pick a power tube driven pre-amp over the hordes of various pre-amp tubes out and why you'd choose LED biasing over other methods. To try it? Some technical reason? Personal preference etc. Without context it's very hard to say anything about your post.
All good questions.

The name Surface started as an adjective, as in an audio amplifier for a Surface tablet computer. Then, as time went on, the adjective became a noun. 

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I choose build a preamp to drive the input of Surface, because inside Surface not enough gain to be driven from just the headphone jack from a laptop computer. I was going to use Surface as the preamp, and have it drive a power amp stage. But, at the last minute, I choose to have Surface driven from an external preamp. I choose to build it as a 6V6 gain stage, as a rebuttal for S***** throwing me off from DYI*****.com.   He did it first , I'm going to do it better....... Although  Surface does not include electronic power braking ( I only use that to generate over-drive tones ),  it does include my take on what a morph control could be.....

LED biasing. I've always used lamp biasing in all my gain stages , audio amps and guitar amps.. .... and no you don't bypass the led bias lamp with a cap... let's just say it's personal preference.

Why a 6v6 tube, instead of varies 12ax(x) tubes ? I read once , it was the opinion saying "big" tubes generate "big" tone. 
I once did a big SE guitar amp using one 12ax7 / T / 12ax7 / 12au7 / EL-34 for the treble tone control channel , and one 12SL7 / B /  12SL7 / 12SN7 / KT-88 for the bass tone control channel , and then mix the both of those into the primary of the O/T ; for a client from Sidney. One could see how I divide the tone stack in half, and then recombine them at the O/T.
Ya , big sound from that one, for sure.........


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