From Teleologis–(at)–orry.noEmail Fri Feb 2 18:26:04 CST 1996
Article: 8907 of alt.guitar.amps
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From: Al
Newsgroups: alt.guitar.amps
Subject: Re: Fender Pro Questions
Date: Wed, 31 Jan 1996 06:58:48 -0600
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Ken Cutler wrote:
>
> Hello to all you Fender Amp heads. I’ve a few questions about my
> blackface Fender Pro Reverb.
> Second question: I was fixing a bad ground (and replaced the power
> cord with a three-wire set-up), and decided to try adjusting the output
> bias by ear. Since then, I acquired a schematic for it, which indicates
> a recommended -51V at the grid bias resistors junction. Should I go with
> this?
The AB165 Pro Reverb sometimes gets a bad rap because it was sold only as a
CBS amp. My guess is it was one of Leo’s last projects! The Circuit is
identical to the highly regarded AB version of the 1×15 Vibroverb and with the
exception of the Middle control, the AB Super Reverb. Kendrick doesn’t like
the output transformer, but if you check the numbers, it’s the same one used
on the Bandmaster!
6L6’s will generally bias properly somewhere between 48 to 55 volts in these
amps. Biasing by current is better, if you’re looking for clean sounds try
between 30 to 35 ma per tube. Of course all the caustions apply.
There are 2 schools of thought on the 470ohm screen resistors. The other is
NOT to increase the wattage rating since these resistors protect the power
transformer if a power tube shorts screen to grid. There is also a 470 ohm
resistor in the bias circuit (next to the diode on the small fishboard). IMHO,
I would rather replace resistors than power transformers. Definately agree
about using flameproof resistors though!
A lot of Pro Reverbs came with Utah speakers. You can get Jensens, either
original or reconed from many Vintage dealers – Check out Vintage Guitar
News-Magazine.
From Teleologis–(at)–orry.noEmail Fri Feb 2 18:26:31 CST 1996
Article: 8926 of alt.guitar.amps
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From: Al
Newsgroups: alt.guitar.amps
Subject: Re: Fender Pro Questions
Date: Fri, 02 Feb 1996 06:57:12 -0600
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Mark Garvin wrote:
>
> In <310F6788.26D--(at)--orry.noEmail> Al
>
> >There are 2 schools of thought on the 470ohm screen resistors. The other is
> >NOT to increase the wattage rating
> Problem with under-wattage carbon comps is that they’d just as soon
> decrease in value as increase. Check the resistance next time you
> see a toasty-looking one.
I’ve seen this happen with originals, but have not experienced any problems
with modern high quality flameproofs doing this. Even so, I’d still
rather blow a tube as opposed to a transformer. In my own amps, I check all
the power circuit resistors whenever I change tubes. Learned about this
after once having the ‘pleasure’ to inform the owner of a nice SVT that his
power xformer was dead because someone who had the amp before was tired of
replacing resistors every time a power tube blew & upped all the wattage
ratings. Ken Fisher also subsribes to this same theory & I believe Kendrick
does too.
