Mic Kaczmarczik's RI Bassman Mods Information

RI Bassman Mods


Fender

RI Bassman Mods

This directory contains USENET articles Mic has saved about guitars, equipment, pickup, techniques, players, and so on. Mic has graciously granted permission to post the stuff on the JT30 page on the off chance that it might be useful in the context of Blues Harmonica. Mic is not responsible for the content, just the collection.

Fender

RI Bassman Mods
From powe--(at)--wdc.com Mon Nov 4 08:51:39 CST 1996
Article: 26469 of alt.guitar.amps
From: O'Connor
Newsgroups: alt.guitar.amps
Subject: Re: '59 Bassman Reissue (Help!)
Date: Mon, 04 Nov 1996 06:12:47 -0800
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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.





 

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3 Spring Reverb Tanks
3 Wire Cord installation
5R4 not enough current
5V4 in BF Deluxe
6550s in Super
68 Princeton Rectifier
68 Super Reverb
6L6 in Champ Again
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6V6 In 6L6 Amp Test
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Bad Fender Mods
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Birth of Fender Reverb
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Blues Deluxe review
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CBS Deluxe Reverb Changes
Champ 8ohms
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diy
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Early Blackfacing
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Eyelet Board Problems
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Fender 6V6 Overvoltage
Fender AA568 circuit
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Fender Amp Covering
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fender
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Red Knob Twin problems
Reduce Champ Screen Voltage
Replacing Glued Baffles
Restoring Grille Cloth
Reverb Amp Effects Loop
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Reverb Pan Bottom
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Reverb Unit Mods Page
RI Bassman Mods
Rivera Designed Fenders
Scrape Vibrato Pot
Screen Resistors
SF Deluxe mods
SF Deluxe Reverb Questions
SF Reverb Cathode Resistor
SF Vibrolux Changes
Shielding Plate Problems
Showman vs Twin
Silverface Changes
Silverface Pro Reverbs
Small Trannys Sometimes Better
Super Champ 6C10
Super Molestation
Super Too Much Bass
Tolex Repairs
Tremolo Tick Tips
Tweed Champ Filter Caps
Tweed Deluxe Bypass Cap
Tweed Deluxe Transformers
Tweed Twins
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Twin Reverb overdrive
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Vibrato Click Fixes
Vibrato Tick Svc Bltn 9
Vibro King fat switch
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Vibroverb tone
What is Hi Pot
What Makes Fender Sound
What Was Ice Cube
Why 68K Input Resistors
Why No More Cloth Wire
Why Silverface Changes

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