Steve,
With your permission I'd like to add this to the information on the W8KC
Virtual Ten-Tec Museum.
Do you have any photos? I sold my Corsair to finance the Omni VI.
73! =paul= W8KC
Collector of Ten*Tecs and other fine plastics.
Visit the Virtual Ten*Tec Museum at http://mywebpages.comcast.net/w8kc
Listen to 7.040 MHz from anywhere with Media Player v9
http://www.w8kc.com/stream.asx
-----Original Message-----
From: tentec-bounces@contesting.com [mailto:tentec-bounces@contesting.com]
On Behalf Of Steve N4LQ
Sent: Sunday, October 17, 2004 1:01 AM
To: tentec@contesting.com
Subject: [TenTec] MOD: Corsair Sinewave Sidetone
TenTec Corsair sinewave sidetone modification:
The sidetone in the Corsair produces a sawtooth wave, rich in harmonics and
is unpleasant to listen to for most of us. Fortunately, there is a very easy
solution.
The Corsair has two audio oscillators. One is the sidetone, activated when
you close the key and the other is the spot feature, activated by pushing
the spot button. Push the spot button and notice how pure it sounds. This is
a sine wave oscillator. We are going to use this for our cw sidetone.
The process is very simple:
1. Turn the Corsair over. Remove the Corsair's bottom cover.
2. With the Corsair's front panel facing you, locate the IF/AF board. It is
on the right, front side of the rig.
3. Locate connector 28. It is located on the left, front side of the IF/AF
board.
4. Using a piece of wire, short the two outer pins of connector 28 together.
I pulled the connector off, stuck the fine wire inside each outer hole and
plugged it back in taking care not to allow the jumper to contact the center
pin. This could be done from the top of the plug. It's you're preference.
5. Turn the volume down completely on the original sidetone.
6. Key the rig and adjust R2 for proper pitch and R3 for desired volume.
Further refinements:
1. To clean up some of the audio thumps, solder a .22uf (224) capacitor
between the center wiper of R2 and ground. I obtained ground from the lug on
the PTO.
2. The original sidetone will leak some of it's nasty tone even when turned
down to minimum. I grounded the front end of R4 which totally kills the
beast. Use the PTO lug for ground. There are other solutions but this one is
easily undone.
Side effects:
The sidetone will now sound very clean. Adjusting the pitch and volume will
not be as easy unless you knock out a hole in the chassis under R2 and R3.
Pushing the spot button will still produce the tone but it will be slightly
different from the sidetone's pitch. This could be compensated for very
easily by installing a trimmer pot in series with the spot button however I
seldom have need for the spot button and the difference is very slight.
Corsair II.
The Corsair II's spot button functions totally differently. Instead of
keying another oscillator, it changes the frequency of the BFO. So from what
I can tell by the schematic this mod will only work with the older Corsair.
Note: When I aligned the BFO oscillators, I set the offset for 600hz instead
of the factory 750hz because I prefer the lower pitch. To adjust the new
sidetone, you can connect a frequency counter to the speaker and adjust for
600hz a pitch. This is strictly user preference.
Note 2. Using an MFJ-281 ClearTone speaker will produce beautiful cw and
reatly reduce some of the anoying thumps associated with the Corsair's agc
and qsk system.
73
Steve Ellington N4LQ
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