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Date: Fri, 31 May 2002 06:07:37 -0400
From: "Chris Hammond"
Subject: Re: Preamp tube subs revisited (was: Bassman '59 RI)

After having done some pretty extensive experimentation with tubes on the
Bassman, I can say with certainty that the response is as I have said. The
explanation I think, is that lowering the gain in the preamp section allows
you to crank the main volume up much higher without feeding back. The
effect is definitely that you get more power tube saturation without
feedback, thus giving you the "desireable distortion". It also gives you
much more "throw" on the volume knob. With all 100X preamp tubes in place
(12AX7's) you have very little variation in the volume control before you
get feedback. Also you get almost know breakup, just really clean harp.
The best distortion or crunch to have is power tube crunch.

>From: John Thaden
>To: Chris Hammond
>CC:
>Subject: Preamp tube subs revisited (was: Bassman '59 RI)
>Date: Wed, 29 May 2002 10:07:14 -0500
>
>
>I was prepared to contradict Chris (see below) when I realized I
>didn't have things straight myself. I think there are different
>cases, but I think you can generally say that changing the gain of
>tubes upstream of the tube that provides the 'crunch' you like is not
>going to affect the volume at which that crunch occurs.
>
>So If the sound you want from your amp comes when (and because) the
>final-stage output tube(s) is being driven past the linear range,
>then swapping in a lower-gain preamp tube (12AY, 12AT, 12AU) will
>have little or no effect on the volume at which that sound is
>produced, but it will increase the setting on the volume control knob
>where it happens, and thus give you more control. If the preamp tube
>gain is ~too~ low, then that sound won't happen at any setting.
>
>If on the other hand the sound you like from your amp comes when and
>because a preamp tube is being driven past the linear range, then
>that tone should be achievable at many different volumes, since most
>amps have a volume knob controlling the gain of the final output
>stage and that gain will amplify the distorted sound. Swapping in a
>lower-gain tube for the one being distorted will generally lower the
>lowest volume at which distortion occurs, but lots of other factors
>about that tube besides its gain will affect the sound.
>
>The prevailing wisdom seems to be that output-stage tube distortion
>is more pleaseing for harmonica than preamp stage tube distortion,
>and that is certainly true on my Blues DeVille. I don't know about
>the '59RIs.
>
>
>
>On Wed, 29 May 2002 05:59:14 -0400, Chris Hammond wrote:
> >As far as preamp tubes, selecting the lower gain tubes lets
> >you get breakup at lower volumes. The lowest of the low is
> >12AU7 which if you put it in slot one (or actually more than
> >one slot) you will get breakup at successively lower volumes.
> >The gain factors for the tube amps can be found on this
> >page
> >
> >http://users.erols.com/bluestat/preampgain.html
>
>
>--
>John Thaden, jjthad~lash.net on 2002/05/29
>
>

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