From powe–(at)–wdc.com Mon Nov 4 08:51:39 CST 1996
Article: 26469 of alt.guitar.amps
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From: O’Connor
Subject: Re: ’59 Bassman Reissue (Help!)
Date: Mon, 04 Nov 1996 06:12:47 -0800
Organization: London Power http://www.wwdc.com/~power/
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> >Help! I bought a ’59 Fender Bassman Reissue because a buddy has one
> >that sounds great! But mine sounds too bright and brittle. I turn the
>
> >treble, presence and bass to “0” and the middle to “5” and I still get
> >the bright sound!! Are there any mods that will “warm up” the amp?
A customer of mine had the same complaints about his “re-issue” Bassman.
The amp is not an exact copy of the 59, so there are a couple of things
you can have a tech do:
1) There are likely to be rattling problems if you try the tube rectifier
route. I installed a couple of power resistors in series with the
solid-state rectifiers to achieve tube-like sag with better reliability
and no tube rattles!
2) Replace the ‘presence’ pot with a 1-meg audio taper
3) Add a pair of 1k5 grid-stopper resistors to the power tubes (one per
tube)
4) Rewire the ‘presence’ control to be a ‘cut’ by: slashing a trace on
the control PCB; move the end of the 4k7 to ground; with a shielded
2-wire cable, tie the new pot across the grid-leak side of the 1k5
grid-stoppers, with a 5nF-400V plastic cap in series with one of the pot
leads (NOTE: You only have to use the wiper and one end of the pot)
5) For best versatility of tube selection; Add a second bias circuit and
connect the existing one to one power tube and the new one to the other.
This allows hum-free performance to be obtained from any set of tubes.
6) Install some 1-ohm current sense resistors in series withpin-8 of each
power tube to ground. This makes reading bias currents a lot easier and
safer (than the transformer-shunt method).
The grid-stoppers roll off the high end a little in the power amp, and
makes the circuit truer to original form. The re-wired ‘presence’ gives
at ’10’ what tone you used to have at ‘1’– now you can smooth out the
highs at will, while a non-zero setting of your ‘treble’ pot allows some
high-end sparkle.
These mods allow a mellow vintage tone to be obtained from the new amp,
with greater reliability.
