Single triode boost?

[Ripthorn]

Okay, so I am building up a tube preamp and will have an unused triode section.  I was wondering if there are any plans for a simple single triode boost.  I could also go with a single jfet boost, but I would like it very simple so that I could use it to drive my last gain stage harder for more distortion.  Any suggestions?

[frequencycentral]

Why not just use the first stage of a Valvecaster as your boost?

[MarcoMike]

well, I guess he's going Hi-voltage on this project, so why going the low volatege way on the booster??
I can't suggest you any specific circuit, but maybe just the simple first gain stage of every old school amp with a volume knob after it... and a switch to insert it before the proper first stage...

when I made my 1987 inspired amp (single input) I wired the unused triode for a switchable 1987<->2204 preamp. I always use it in 1987style mode... but at least the triode is not completely unused... now actually a simple booster would have been a nicer feature...

[frequencycentral]

well, I guess he's going Hi-voltage on this project, so why going the low volatege way on the booster??

The Valvecaster at higher voltage just gives more boost and clean headroom. You can apply whatever B+ you want to it (within reason). That boost stage at 70 volts is an untamed beast of a boost. And very simple to implement.

[MarcoMike]

first of all... sorry for a bit of dyslexia today... I don't know where "volatege" came from...

and... ok.. I've never tried the valvecaster... and didn't know about experiences at high voltage.... so, why not!

[frequencycentral]

first of all... sorry for a bit of dyslexia today... I don't know where "volatege" came from...

Though I would replace the 50K gain pot with a 100K, it will give more range of cleans. And put a small value resistor between the gain pot and ground (maybe 4K7 ?) - that pot can 'thunk' when maxed out as the cathode directly connects to ground. You'll know what I mean if you breadboard it - then you can experiment with the resistor value to avoid it.

[Ripthorn]

I looked at the valvecaster, but totally spaced using just the first stage.  I am still trying to decide if it would be better to put the boost before the first input stage or before the first "high gain" stage.  I guess I will just have to try it, now won't I?  I guess I could also look at the fetzer, since they took that from a 12ax7 stage anyway.

[Mike Burgundy]

Weeeellll... It all depends, as always, on *what you want to achieve*.
Same basic sound (aside from possible poweramp OD, etc) but louder: stick it at the back.
Slam more gain into clean (for that bluesy edge) and/or into dirty channel (soaring leads?) - stick it at the front.
If you want it solely as an extra-high gain solo boost, you'll probably want some etra voicing too - some cutting of lows perhaps.
Component selection is highly dependant on periphery and requirements (supply voltage, bias point choice, desired gain, desired frequency response), but I'd say copying the first input stage is a good place to start. Stick it where you'd like it to be and tune from there.



Randall Aiken has excellent stuff on his site (aikenamps.com) on designing tube stages.

hih

[Ripthorn]

I haven't been to aiken amps, so I will definitely check that out.  Thanks for bringing up those points, they give me some very good food for thought.