I am considering adding a product detector to my S40A. Has anyone used a
6SN7 to replace the 6J5 BFO and feed the IF signal to the grid of the second
triode with the cathodes tied together? The original oscillator circuitry
would be wired to the first triode. Audio from the plate resistor of the
second triode (after IF filtering).

--
Kind regards,
Terry Judkins


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TerryJ wrote:
I am considering adding a product detector to my S40A. Has anyone used a
6SN7 to replace the 6J5 BFO and feed the IF signal to the grid of the second
triode with the cathodes tied together? The original oscillator circuitry
would be wired to the first triode. Audio from the plate resistor of the
second triode (after IF filtering).

No, but I do have an SX-99 with a product detector already installed in it,
which I have no real need for any longer. It has a Collins mechanical
filter of unknown width and extremely low audio output. I think it was
originally done according to the QST article but I am not sure. It's
definitely a project set but make me an offer.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

TerryJ wrote:

I am considering adding a product detector to my S40A. Has anyone used a
6SN7 to replace the 6J5 BFO and feed the IF signal to the grid of the second
triode with the cathodes tied together? The original oscillator circuitry
would be wired to the first triode. Audio from the plate resistor of the
second triode (after IF filtering).

I'm sure its been done but the question is why would you want to?
Ok, its fairly deaf on 20 SSB and really deaf and getting quite unstable
for SSB on 15. Forget 10. Its more than adequate on 40 and 80 if you
ride the controls the way you should. I don't see where a product could
offer any improvement.

-Bill

"TerryJ" ) writes:
I am considering adding a product detector to my S40A. Has anyone used a
6SN7 to replace the 6J5 BFO and feed the IF signal to the grid of the second
triode with the cathodes tied together? The original oscillator circuitry
would be wired to the first triode. Audio from the plate resistor of the
second triode (after IF filtering).

You'd be wanting QST for April 1954. "Modifying the S40 for S.S.B. Reception"
by Edward Sommerfield. It's also reprinted in the ARRL's "Single Sideband
for the Radio Amateur", first edition which came out in '54.

He adds a crystal filter for selectivity. Then a third IF stage to compensate
for the loss in the filter. He injects the BFO into the grid of this stage,
complete with a front-panel control for injection level. He changes the
detector to a 1N34 diode, but it's still an envelope detector.

He even shows a means of modifying the existing BFO for crystal control.

At a glance, he also ads a stage of audio, to componsate for the (likely)
use of the RF gain control to cut back on gain.

He adds a VR tube to regulate the voltage going to the local oscillator
and BFO. He even adds a tuning eye tube.

Michael VE2BVW

Hallicrafters must have used those mods and built the SX99.
Looks like I am reinventing the wheel. I have made a few changes
(reversable). I replaced the RF amp 6SG7 with a 6AC7 with appropriate
changes to bias, AGC and screen voltage, replaced the 6SA7 with a 6SB7Y and
replaced the first IF with a 6SG7. I also added a tuning eye which plugs
into the S meter socket and added a zener regulator to B+- for the BFO. It is
a VERY sensitive and stable receiver. SSB reception is just OK though.
+ACI-Michael Black+ACI- +ADw-et472+AEA-FreeNet.Carleton.CA+AD4- wrote in message
news:ccfv7m+ACQ-c3a+ACQ-1+AEA-freenet9.carleton.ca...
+AD4- +ACI-TerryJ+ACI- (suptjudno+AEA-comcast.net) writes:
+AD4- +AD4- I am considering adding a product detector to my S40A. Has anyone used a
+AD4- +AD4-
+AD4- You'd be wanting QST for April 1954. +ACI-Modifying the S40 for S.S.B.
Reception+ACI-
+AD4- by Edward Sommerfield. It's also reprinted in the ARRL's +ACI-Single Sideband
+AD4- for the Radio Amateur+ACI-, first edition which came out in '54.
+AD4-
+AD4- He adds a crystal filter for selectivity. Then a third IF stage to
compensate
+AD4- for the loss in the filter. He injects the BFO into the grid of this
stage,
+AD4- complete with a front-panel control for injection level. He changes the
+AD4- detector to a 1N34 diode, but it's still an envelope detector.
+AD4-
+AD4- He even shows a means of modifying the existing BFO for crystal control.
+AD4-
+AD4- At a glance, he also ads a stage of audio, to componsate for the (likely)
+AD4- use of the RF gain control to cut back on gain.
+AD4-
+AD4- He adds a VR tube to regulate the voltage going to the local oscillator
+AD4- and BFO. He even adds a tuning eye tube.
+AD4-
+AD4- Michael VE2BVW
+AD4-


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Hi Terry:

I think your idea of using the 6SN7 is better than the '54 QST article. The
6SN7 makes a great product detector with 1/2 as the bfo. Not a lot of work.
Audio might be a bit low, but you can cheat and use a transistor audio
preamp powered by the cathode voltage developed by the audio output stage as
a voltage source. I used a similar arrangement in an ARC-5. Just do not
tell any of the diehards that you have a transistor buried under the deck or
they will take you out of their will.

Re-inventing the wheel is not all bad

73, Colin K7FM


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