Ken Moon...question for you

[iknowjohnny]

In a old post where someone was asking about paralleling triode stages you mentioned that in an amp like a plexi or such that it would be particularly advantageous to do that ans you suggested another use of the extra stage. This quote is yours from that thread..

I'd rather use the extra triode for another gain stage (a 2k7/100k unbypassed stage up front is popular - some even call this a "tubescreamer" stage, because the effect is similar to using a TS9 as a booster in front of the amp

I bring this up because i love the way a tube screamer sounds in front of an amp as a clean boost. I don't want to add more gain tho i know it will. I can always dump some down the line tho. Can you tell me in what way it sounds like a TS up front? Does it add that mid bump or what? And how close to unity gain would a 2.7k cathode unbypassed be?

[Ken Moon]

I've seen that reference a few times over the years on different amp forums - I think it got that name as more of a general description than as a technical description. There may be more history to the term, but I don't know it - the first time I read it, it was referring to modding JMP Marshalls into JCM800s.

Adding another gain stage will definitely increase the amps "gain" (gawd I hate that term), in that no matter how it's biased, it's still going to have a voltage gain of around 50.

If by 'gain' you mean distortion, it will usually add that too, depending of course on the rest of the amp.

I don't have time at work today, but if you go over to Merlin's Valve Wizard website, or to Randall Aiken's website, you can see how to calculate the frequency response and gain of a 12AX7 stage with an unbypassed 2k7 cathode resistor, at whatever preamp B+ the amp in question uses, and compare that to a TS EQ curve.

I'm not an expert on the freq response curve of a TS, but there are some articles out there that get into it in excruciating detail - here's one:

http://www.geofex.com/article_folders/t ... sxtech.htm

and here are links to the other sites I mentioned:

http://www.aikenamps.com/CommonCathode.htm
http://www.freewebs.com/valvewizard1/Co ... _Stage.pdf

[iknowjohnny]

I see. So i guess when they refer to it like that they are basically just saying a uncolored signal boost and tubescreamer just happened to be the description used probably because they are so common as boosters.

I tried paralleling the spare stage i have after $hit-canning my cathode follower with the last stage b4 the tone stack last nite. I left the plate and cathode values the same tho, and i'm not sure it made any difference to the good, but it's definately subtle. Suppose i should 1/3 all the values as was said in that thread except the bypass cap which they said to double and see what happens. Thanks for the reply