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Date: Mon, 9 Apr 2001 20:38:57 -0400
From: "STACHNIK,GEORGE (HP-Cupertino,ex3)"
Subject: Amp Mods

I read Gerald Weber's article on "Harp Amp Secrets" from
the May issue of Vintage Guitar with great interest. I'm
now looking at some of the older amp's that I've accumulated,
(and found to be less than stellar for playing harp through)
with a whole new level of interest. If anybody actually tries
some of the things that Gerald suggests in his article, let
me beg you to *please* share your experiences with the list.
This article looks like it could be the beginning of a wealth
of good techniques for making amps more harp-friendly....

I have an old Gibson GA-5 Skylark. One of the problems with
Gibson amps is the fact that Gibson used the same name and
model number to describe so many different amps. The one
that I have is an oddball - it uses 6AQ5 power tubes,
a 6EU7 preamp tube, and a 6C4 in between the two. If you'd
like to see a schematic of my amp, there's one online at
http://schematicheaven.excelland.com/gibsonamps/ga5_crest.gif
The schematic says it goes with a Gibson Crest, but so far,
it sure looks like my Skylark. (BTW, the same circuit is
also very close to an Epiphone EA-50, which I hear is also
quite a good harp amp...)

The tone that I am getting out of the Skylark is quite good.
The amp is positively killer when you play guitar through it.
But when I play harp through it using either my Shure GB or
my JT-30, it has a shrill quality - very much like what
you get with a Fender amp *before* you substitute lower-gain
12AU7 or 12AT7 preamp tubes for the 12AX7s that come stock.
I have sought in vain to find a tube substitution for
the 6EU7 that would make this a more harp-friendly amp. So
now (per Weber's suggestion), I'm thinking about lowering the
plate voltages, and increasing the value of the coupling cap's.
I'd be very interested in hearing any experiences that other
harpitologists may have...