[Harp-L] Re: Webster Chicago 66-1A Amp

[HTownFess <Spschndr@xxxxxxx>]

I have two of those.  They were meant to be driven mainly by a crystal
phonograph cartridge that had a much higher output than today's
cartridges or even a mic, so they don't have an input stage--they're
just a low-gain phase inverter, a push-pull main stage, and a
rectifier to power them.  The volume knob is right on the input, and
the tone circuit is like top boost on an AC-30, just phase-canceling
across the output stage.  A mic straight in does very little, but
putting a preamp in front of it gets it going, as you found: it needs
another gain stage.

The phase inverter is a paraphase type and has a little gain on each
triode, so I rewired the PI socket for a 6SL7 and added a 50 mfd
bypass cap on each cathode, used 1K cathode resistors, all to boost
gain.  0.1 mfd coupling caps and a 47 mfd. first filter cap to fatten
it up, 5Meg pot on the input to try to get more signal in.  It came
out kinda cool--gets going without a preamp now, though only near the
top of the volume knob.  The original alnico Oaktron speakers don't
last long under the beating, and ceramic Weber Signature 8s fit in
there.  I have used both the ribbed and smooth cone versions, no
decided preference there.  It is about as loud as a healthy Champ,
does not feed back easily.  The metal chassis parts and grille screen
will rattle and bang if you get the amp going too hard, holds the amp
back a little, as does the undersized rectangular speaker opening--
it's entirely possible that they designed it around oval speakers and
switched to round ones without changing the cabinet.  I built
extension speaker jacks into mine and it will push a 12" okay, though
I wouldn't call a 66-1A 15 watts even with a preamp in front.

I modified mine because I didn't want to carry around a preamp too.
The 66-1A is good components in an interesting box.  Sams Photofacts
folders for it w/ schematic are out there.

Stephen Schneider

On Feb 23, 11:23 am, Michael Posey <harr...@xxxxxxxxxxx> wrote:
> Just picked up a Webster-Chicago 66-1A. Believe it was manufactured about 1947-48. 15 watts, 8" speaker, 2 6V6, a single 6N7 preamp tube and a tube rectifier. Looks like a small burgundy colored suitcase. Pretty stiff running straight from a mic. Put my pre-amp and DM-3 in the chain and this little thing screams!  Anybody else using one of these? I get a few hits on the web but nothing in the harp-l archives. Thanks
>
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