[Harp-L] Re: Fender Pro Jr....



While swapping twin triodes of different characteristics without
circuit (mainly cathode and plate resistor value) changes may result
in the tube operating with less gain or more distortion, this
"suboptimal" condition may be beneficial in a harmonica amp.  I think
that many harp amp tinker-ers do this with favorable effects.  Concern
is sometimes voiced about the ability of amps to safely use a 12AU7
because of the increased current demands of this tube, but I have not
noted problems with this sub.

Jim R

On Jul 8, 1:09 pm, "Joel B. Chappell"
<joel.b.chapp...@xxxxxxxxxxxxxxx> wrote:
> You really can't [make that shouldn't] capriciously swap dual triodes
> 12AX7,12AU7, 12AT7, 12AY7 etc. around as each type has a different
> transconductance curve thus a different plate impendence for each type...
> which really suggests that you change some other discrete components else
> you may buy some additional distortion... loss of gain etc. Understandably,
> I realize the guitar boys want more distortion. In all actuality the 12AY7
> has the lowest noise figure. If you were to re-bias the circuit to take
> advantage of its gain and run DC on its filaments you would reap some
> worth-while benefits, otherwise if your amp has a 12AX7 in the socket, leave
> it there. The chap that designed the amp knew what he was doing, at least
> back in the day he did.
>
> Joel B. Chappell
> 21 Billings Street
> Milford, NH 03055
>
>
>
> -----Original Message-----
> From: On Behalf Of Splash!
> Subject: Re: [Harp-L] Re: Fender Pro Jr....
>
> You can't have mine.  I'm keeping it.  =8^D
> Great little amp.  I tried several vintage tubes of lesser gain in V1 and
> went back to a 12ax7.
> Tones deep into my bones!
>
> When life asks you to jump in...
> Splash!- Hide quoted text -
>
> - Show quoted text -




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