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Date: Fri, 31 May 2002 14:41:22 EDT
From: Markburne~ol.com
Subject: Re: Preamp tube subs revisited (was: Bassman '59 RI)

Hi all,

FJM has a point, different brands of 12AX will display different
characteristics...some of the best sounding Bassman RI's I've heard had all
12AX preamp tubes. Subbing preamp tubes in a Bassman amp is worth
investigating but it is one factor...not a "be all & end all".

However, there is more going on than just different gain values, lower gain
tubes usually draw more current and runs less voltage on the plate in the
same circuit. This can sound warmer/softer, but may lack punch. Higher gain
tubes will have more low end. If your amp sounds harsh/brittle you might
prefer lower gain tubes, if your amp has a "soft" sound with little front on
the note you might prefer higher gain tubes (assuming you have that option)
-
the point being that different players (and mics) sound different and have
different requirements. For example I prefer 12AX's in my Twin, but another
player I know sounded the best I'd ever heard him when I tested it at a jam
with a 12AY...which I hated.

Part of the logic in going to lower gain tubes in an RI Bassman is that this
is what they came with, they also ran lower voltages (I guess that a '59
might run around 170-190v on its plates with AX's fitted, compared to
240-250v on the stock RI). An RI fitted with AX's is unlikely to sound much
like the original though that's not to say it won't make a good harp amp.

My findings are rather different to John Thaden's, fit a 12AU phase inverter
and your crunch might not happen... at any volume. But I agree that output
distortion is what most people are after, keeping a high gain tube in the
phase inverter helps push the output stage. I always preferred a 12AT in the
middle position when my amp (Bassman RI) was stock. Colder biasing of the
output tubes can also help.

Another factor is how loud are the people you are playing with. Sometimes
you
might hae to sacrifice tone and go with lower values just to free up some
headroom and save yourself dancing about on stage to avoid feedback. An amp
that sounds cool in your living room might be as much use as a chocolate
fireguard when you put bass and drums behind it.

Regards, Mark.