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

[Rick Davis <bluesharpamps@xxxxxxxxx>]

"You really can't [make that shouldn't] capriciously swap dual
triodes 12AX7,12AU7, 12AT7, 12AY7 etc. around..."


Yes, that is right.  However, the 5751 can be swapped in place of a 12AX7
without any worry about incompatibilities.  The NOS JAN Philips  5751 is an
industrial-quality version of the 12AX7 with 70 percent of the gain, and a
warmer sound, to my ear.

-- 
-Rick Davis
The Blues Harp Amps Blog
http://www.bluesharpamps.blogspot.com/


On Fri, Jul 8, 2011 at 12:09 PM, Joel B. Chappell <
joel.b.chappell@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!
>
>