From PYLO–(at)–su.edu Sun Feb 4 17:46:55 CST 1996
Article: 9082 of alt.guitar.amps
Path: geraldo.cc.utexas.edu!cs.utexas.edu!news.eas.asu.edu!news.asu.edu!ppp2-16.INRE.ASU.EDU!PYLOT
From: PYLO–(at)–su.edu (Ruth and Dale VanZile)
Newsgroups: alt.guitar.amps
Subject: Re: BF conversion for Bassman?
Date: Mon, 5 Feb 1996 01:06:32
Organization: Arizona State University
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In article <4erpt5$7i--(at)--ark.ucdavis.edu> ez00455–(at)–oris.ucdavis.edu (George Kaschner) writes:
>A lot of the detailing comes down to not
>only component selection but lead dress – how a particular wire gets from
>one place to another. Even if you match component values and lead dress,
>you may find that the power transformer is giving a higher voltage to the
>tubes.
Lead dress is the biggest change, and is most likely what necessitated all the
extra parasitic oscillation supression (all those ‘extra’ caps). See, UL
decided that they wanted to see a plastic-insulated wire in the amps, for
increased safety. This forced a change in lead dress, as the plastic wires
tended to melt and short out when run under the tagboard like the older amps’
cloth-covered wire was. So, the wires were moved, and then parasitics started
showing up due to the lead dress not being as good as the old, original amps.
Since they didn’t have Leo there any more telling them not to do it, at this
time, the engineers decided to add that wierdo cathode resistor and cap to the
output tubes, to get rid of all that unwanted distortion. A good idea for
hi-fi, a bad idea for guitar. BTW, I’ve seen Bassman heads with the
cloth-coverd wire clear into early ’68, SF with aluminuminum trim and all, so
you’re probably still wired with it…
>Before you even start modding the silverface, make sure it is working up
>to spec.
Before you change anything, look at your tube chart for AB165 or AA864. Then
look inside for the cloth-covered wire. If you have both of these, you don’t
need to change a thing…. Then:
>Check the power supply filters,
Look for white powdery or globby stuff oozing out of the positive end
(usually) of the caps. If they’re not oozing, leave ’em alone….
>put in fresh tubes, and properly bias the amp.
If the thing needs ’em. Look at the power tubes in front of a white sheet of
printer paper, in good light. If you see any brown deposits on the glass
(called ’emission burns’) and/or a brown ring around the getter flashing (the
silvery stuff on the inside of the tube’s glass envelope), start saving for
new tubes. Try the Sovtek 5881/6L6WGC, as they’re really solid, and many
people (myself included) like the tone.
>Then, carefully consider the impact of each
>change you make. Don’t get caught up in making sweeping changes
>throughout the amp at once. If you want to learn how the changes affect
>the amp, make one mod at a time and listen to the effect before you
>proceed to another. Consider keeping a log of changes made and their
>result. That way if it starts sounding ratty ( I almost said “like a
>Torres”) you can change it back.
Good advice…
Dutch
