amp mod for harp

[Dina Janzen and Jim Rossen <dlj@xxxxxx>]

John-  I would like to learn of the details according to Weber.
I have installed a cap across the preamp tube plate resistor on several
amps. I am running a Princeton Reverb and a Gibson GA40 with this now.  It
works.  Caps of 1000 pf to 1500 pf are typically suggested, but I have had
good luck with 2200 pf (same as .022 mfd) caps.  The cap is soldered with a
lead on either side of the plate resistor (parallel connection).  The power
supply line supplying the plate resistor is at AC ground so the effect is to
bleed off treble to ground,  decreasing the the treble signal directed to
the next stage of the amp.  Caps should be rated for high voltage operation.
250-350 V is an approximation of the power supply voltage to the preamp
plate resistors, so caps rated at 600 V or more would be my choice.  I have
used them on the first gain stage.  It probably works on other stages as
well.   I doubt  that the idea originated with Weber or that a description
in one's own words of the content of his article would be a copyright
infringement.  

Jim

> 
> Date: Sun, 27 Jul 2003 15:47:36 -0700 (PDT)
> From: john kuzloski <jkuzloski@xxxxxxxxx>
> Subject: amp mod for harp
> 
> The "cap across the plate resistor" trick for rolling
> off highs (thus helping eliminate feedback and
> allowing more use of the amps tone controls) is
> described by Gerald Weber in the September 2003 issue
> of Vintage Guitar, pp. 106-7.  I'm not sure how much
> more I can say without infringing on copyright.  Email
> me if you have any questions.  Gerald Weber is the
> author of "Harp Amp Secrets and Tips" that many of you
> have already seen at the jt30 website.
> 
> Anybody have any experience with or thoughts about
> this modification?