Tubes Tubes (ping Eric)

[Harry Bissell]

I have a Fender Twin which I modified to allow use of one pair of output
tubes at a time (or both) One 6L6 pair is wired as a triode, one as a
pentode.

The triode pair has lower output, less power supply rejection (more
backgrond hum) and clips at a lower level, but it is a soft "spongy"
clipping.

The Pentode pair has higher output (maybe 25-20%), much less hum, and stays
clean until clipping (which is "harder" or more fuzzy then the triode).

So the comments about high order harmonics are probably correct...

Which one is preferred is another story... If I had to choose just one...
I'd go Pentode...
But IMHO the best is to run them both together... at low levels they track
fairly well, but then the triodes fart out leaving the pentodes to carry
the load alone until they chip also...
A nice rich sound at all levels...

Why the poor hum rejection for the triodes ???

You got your ears on Eric ????

:^) Harry (who won't say you're crazy for having a tube guitar amp... only
for lifting it) Bissell

(The twin I have weighs 90lbs...)



Hallgeir Helland wrote:

> Don Tillman wrote:
> >    The tube transfer curve is somewhat linear in that the harmonic
> >    distortion is almost entirely first and second harmonics.
> >
> > Arrggh!  Of course I meant second and third harmonics.  Both from the
> > transconductance curve of the tube and from the dynamic variation in
> > plate voltage.
>
> I've been told that there's a significant harmonic difference between
> triodes and pentodes in the output stage of a tube power amp:
> triodes have far less harmonics from the fourth order and upwards, than
> pentodes do. (this is when the output stage is slightly overdriven)
>
> So triodes are favourites in the output stage. Preferably single ended,
> class A and zero feedback. :-)
>
> Tell me if I got it wrong.....
>
> thanks,
> Hallgeir
>
> --
> .,.,.,.,.,.,.,.,.,.,.,.,.,.,.,.,.,.,.,.,.,.,.
>  Hallgeir Helland   hhelland at mailandnews.com
>     Evlogia           http://fly.to/evlogia
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