[R-390] R-392 Audio Module

Sun, 10 Nov 2002 20:31:58 -0800

Barry,

Without aligning myself in any way with something that can only be viewed
with disgust, I do have to point out that modern low impedance solid state
audio output modules do not need coupling transformers to match the 4 to 32
Ohm speaker impedances, but do need a means of de-coupling the speaker from
the DC potential present at the complementary symmetry output connection.
Hence, the large electrolytic...

The module was probably capable of some Watts of power output. The larger
the cap value, the more power to you, Buckaroo, especially at the low
frequency end. Imagine Amperes of current through the cap to a woof-woof...

Bob

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Barry Hauser
Sent: Sunday, November 10, 2002 7:50 PM
To: [email protected]
Subject: Re: [R-390] R-392 Audio Module

Hi Gang:

No -- not that audio module, but an oddball retro-fit.  Once again, a toob
radio turns up on my doorstep with something other than all tubes plugged
into it.

This one is Model 1240 audio amp made by Epitek Electronics, Ltd. of Ottawa.
It's about 1 X 2 inches and a bit over 1/4" thick with an aluminum plate
(probably a heat sink).  The back is marked "R-76-49"

I found this, along with a 1000 mfd 50v electrolytic, stuffed into the cubby
where the 26A7 is supposed to go and secured with masking tape. (yup)  It
looks like the cap tossed its cookies.  There's also some white stuff around
one corner of that module, but I don't know if that's an inside job or not.

Anyone know anything about this module.  Obviously a home brew addition.
Only 5 solder-on terminals -- "GND" wired to pin 2 & 7 (grounded) of the
tube socket, "IN" - wired to pin 3 (which makes some sense), "+40" - hooked
to pin 6 (26v filament).  "OUT" is wired to pin #1 of J613 -- bypassing the
output transformer and going directly to the audio out.

The fifth terminal is marked "CAP" and connected to the negative lead of
that electrolytic.  The positive lead was just dangling -- apparently
disconnected itself and it looks like it was originally tacked onto the
"OUT" tab.  Does this make any sense -- a 1,000 mfd cap from the output to
what?

It also appears that the original wiring was left unmodified to the tube
socket - there's some instances of "tack soldering" which suggests
tentativeness (i.e. "It still don't woik!")

Anybody have any info on this module?  Any suggestions?  Probably doesn't
pay to mess with it -- I'll probably pull it out and re-tubify the audio.

Barry

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