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The 12AU7 has about 19% of the gain of the 12AX7 - not much signal
amplification at all - I'm not surprised at the effect! Personally,
I don't think I would substitute anything other than a 5751 or a
12AT7 - just my preference.
In case you haven't seen it, The Tube Store has a cool pre-amp tube
substitution page that's worth checking out. Here's the link:
-Dick
--- In , James Barnett
<elreydelart@e...> wrote:
> A pal and I tweaked our reverb units this past weekend and we
found a 12AU7
> instead of an AT7 made 'em nice and mellow sounding (but maybe not
as deep).
>
> At 03:54 AM 9/27/2003 +0000, you wrote:
> >Here's my $.02 on your tank issues:
> >
> >The 5751 tube has a bit more gain than a 12AT7 (the 5751 has about
> >70% of the gain of a 12AX7, while the 12AT7 has about 60% of the
> >gain of a 12AX7), so you may want to try a 12AT7 to reduce some of
> >the harshness.
> >
> >The 7025 tube was a low noise version of the 12AX7 - I don't think
> >they're really in commercial production now (although Sovtek may
> >have such a model). Any 12AX7 should work fine in the tank. I
think
> >the tank tube chart reference to the 7025 is for "authenticity"
> >reasons in the reissue.
> >
> >Even with the cap mod (and with old 6K6, 12AX7, and 12AT7 tubes in
> >place), my reissue still has a good bit of the treble-y "ice pick"
> >effect (at least when compared to the 6G15 tank I built). Don't
> >know if you'll ever get "full tone control", but maybe a 12AT7
will
> >take a little edge off of the tank. Good luck!
> >
> >-Dick
> >
> >--- In , "rio452001"
<mpietra102@a...>
> >wrote:
> > >
> > > I recently got one of the Blackface Reverb Reissues from MF.
> > >
> > > It arrived with the RCA connection from the tank unplugged,
so I
> >had
> > > to fiddle around with that first, and then after I got the
reverb
> > > working, I couldn't turn the tone past "1" due to the harsh
high-
> >end
> > > thing.
> > >
> > > I was aware of the issue from the various posts here, so I
headed
> > > over to my local used/vintage instruments shop to pick up a 6K6
> >and
> > > AT7. I ended up with a Marconi 6K6 ($15Cnd) plus a back-up. But
> > > instead of an AT7, the amp guy suggested a 5751.
> > >
> > > That allowed me to turn the tone control to "3".
> > >
> > > Mainly I play a '65 Jaguar through a '66 Bandmaster, and the
> >reverb
> > > sounds very nice, but I suspect it could sound even better if I
> >had
> > > full tone control.
> > >
> > > Would the AT7 be preferable to 5751 (Sovtek, no less)? Should I
> >look
> > > for a 7025? Is there anything else I can do, short of the cap
mod?
> > >
> > > Incidentally, like someone else has noted here, the tube chart
on
> >the
> > > inside of the unit refers a 7025, but it came with a (GT)
12AX7 in
> > > its place.
> >
> >
> >
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messages,
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> >
> >
> >
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