Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: nepalnt21 on April 03, 2021, 08:55:09 pm

Title: considerations for a SS preamp with valve output stage?
Post by: nepalnt21 on April 03, 2021, 08:55:09 pm

hello, new here.

    i have never worked with high voltage, and will ABSOLUTELY be reading all relevant literature and taking ALL necessary precautions BEFORE i attempt any amp building or modification, so there's that out of the way.

   i have dabbled with electronics, including guitar pedals but am still a novice.

     basically, once i learn everything i can, i plan to go for a single ended class A design (i'm thinkig champ, i really also like those tiny valco/ supro amps a whole heck of a lot), and i have been led to believe i like el34s the best (but would like to be able to trial 6v6, kt66, etc. if possible)... but i honestly do not like the sound of preamp tube distortion, and would prefer to design my own solid state preamp.

     aside from being able to supply power correctly to the solid state and tube side, what considerations do i need to keep in mind when designing the preamp?

i'm thinking along the lines of >>> what voltage/ amperage does the guitar signal need to be, and what circuitry would i need between the last component of the preamp and the first component of the power tube stage?

Title: Re: considerations for a SS preamp with valve output stage?
Post by: TIMBO on April 03, 2021, 10:42:09 pm

Welcome
I had no trouble marring the two together...
https://www.guitargear.net.au/discussion/index.php?topic=45138.msg502523#msg502523

Title: Re: considerations for a SS preamp with valve output stage?
Post by: thetragichero on April 03, 2021, 11:09:20 pm

dual rail supplies (+/-15v) seem to be popular with solid state preamps. i would run them off a separate transformer winding (~22vac needed for a full wave bridge, slightly more will allow you to run linear voltage regulators, 7815/7915 for example)
voltage needed to drive the tube would depend on the tube and its operating conditions. datasheets are your friend

Title: Re: considerations for a SS preamp with valve output stage?
Post by: PRR on April 04, 2021, 12:16:30 am

> i honestly do not like the sound of preamp tube distortion, and would prefer to design my own solid state preamp.

It is perfectly possible to make a 6V6 cry without straining the preamp. "Preamp distortion" usually needs some mis-design to happen conveniently. You can certainly devise a SS preamp you won't like.

The AA-Champ is your all-purpose starting point. Build that, then mod.

Title: Re: considerations for a SS preamp with valve output stage?
Post by: nepalnt21 on April 04, 2021, 05:35:42 pm

ok, great stuff!

thanks for the replies.

are those rca 6973s i see for sale online at a certain tube store in texas legit? i thought they were unobtanium and i can apparently get them sent to my house for under a hundred bucks per matched pair. sounds too good to be true.

if it *is* true, and i get one or two, will i just need to check the datasheets and change the resistor at the power tube cathode to match what i need for a 6973 in a champ type circuit?

thanks again, everyone;

gives me more to learn and think about, which i like.