Reconditioning Checklist

From larr–(at)–erakusa.com Fri Sep 1 22:58:54 CDT 1995
From: larr–(at)–erakusa.com (Dr. Nuketopia)
Newsgroups: alt.guitar.amps
Subject: Re: Revive my BandMaster
Date: 1 Sep 1995 16:04:43 GMT
Mime-Version: 1.0

In article <425s1v$q9--(at)--ews.continuum.net>, griggs–(at)–.continuum.net
says…
>
>I have a circa 1967 Bandmaster amp and it is tired. Symptoms:
> weak output, not (as much) punch, acoustic feedback when the
> head is on the speaker cab. It has been modified by replacing the
> 6L6GC’s with RCA 7027A’s fixed bias (50 ma idle). I checked the
> cap ripple and it seemed reasonable. Nothing else has EVER been
> done to this amp. What do the guru’s suggest? New Tubes? Whose?
> From where? New caps? OK. New speakers? I’m game. This used to be
> a solid amp.

Here is how I would do it:

Check the C- power supply rectifier: If it is a selenium rectifier stack,
replace it with a silicon diode. You may have to add a resistor or change
some values in the bias supply to compensate for the new diode’s
higher efficiency.

Replace all the tubes with the spec’ numbers for the amp. The Sovtek
5881’s are great replacements for the 6L6GC, and reasonably priced. Stay
away from the Chinese tubes. Either go Russian or N.O.S. American or
European tubes. Make sure your output tubes are matched pairs.

Replace all elctrolytic capacitors. Use the +20/-0 value rule. i.e. try
to up the values by 20%, but never less than the stock values. Always be
careful to get the CORRECT working voltage capcitors.

Examine all the critical signal coupling capacitors, replace any
wax/paper caps with metal film (mylar or polypropelene, Sprague “Orange
Drops” are pretty good)

Resistors that have gone off value should be replaced with new metal film
resistors. Pay special attention to the values of resistors used in the
critical phase-inverter/driver stage. Use 1% tolerance resistors here.

Pay special attention to carbon-composition resistors. Often, the leads
will seperate from the resistive material inside and form intermittant or
microphonic connections.

Clean all the pots.


Dr. Nuketopia
Technology Director of the World-Wide Monetary Conspiracy
Opinions strictly reflect the party line

 

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