From tremolu–(at)–ol.com Tue Dec 20 11:19:17 CST 1994
Article: 35142 of rec.music.makers.guitar
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From: tremolu–(at)–ol.com (Tremolux)
Newsgroups: rec.music.makers.guitar
Subject: Re: Help: Biasing 5881’s in a Deluxe Reverb
Date: 19 Dec 1994 23:27:05 -0500
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Reply-To: tremolu–(at)–ol.com (Tremolux)

Careful making blanket statements like that regarding biasing, or someone
will blow up their amp. The LAST thing you would want to do is put 5881s
in a Deluxe and bias them for 50 ma per tube. No way, Jose!!!

The Deluxe power supply and output transformer were not designed for
anything near that. I run mine (I have Russian 5881s in my 64 Deluxe
Reverb) at 30 ma per tube, and this results in the output transformer
primary winding dropping over 5 volts between center tap and plate due to
IR losses. Any more would be too much. The 5881s in my Deluxe give it a
real strong and clear clean tone with mondo low end, and a sweet high end
as well.

Bear in mind that the Deluxe’s magnetics were not designed for 5881s, so I
have measured the output at 25 Watts at the onset of clipping. I’m
running a solid-state rectifier in it, and I have replaced all the
electrolytic filter caps (originally 16 uf–(at)–450V) with 22 uf–(at)–500V
units, in order to stiffen up the supply a bit for the 5881s.

This is not to sell short the 6v6s. These tubes sound great, if you can
get NOS American tubes. The current production Russian and Chinese 6V6s
suck big time. The Groove Tubes 6V6HD is NOT a real 6V6, it’s really a
wimpy Russian 6L6, so forget it. I put in the 5881s specifically to get
the thing to go as loud as possible before breaking up, and it worked. In
the Deluxe, the 5881s are dead reliable.

The 50 ma bias figure sounds more like Calss A operation to me. Class A
amps usually run at lower plate voltages so as not to over dissipate the
tubes since they run at high idle currents. Don’t try to get an amp
designed for Class AB1 to run Class A, because the magnetics probably
won’t take it.

In amps designed for 6L6/5881s from the beginning, such as Super Reverbs,
etc., the right AB1 bias value is around 35 ma. The 50 ma value will
result in the power transformer running really hot (maybe too hot),
probably hum due to inadequate filtering for this current level, short
tube life (they would really be cooking), very early break-up, and
probably a somewhat mushy sound.

Sorry, Omar, but I disagree with you on this one, without your putting in
any qualifiers.

Regards.