A Two Tube transmitter
After using my improved 3 tube superhet in the 2001 AWA OT CW contest I felt the need to improve my 6L6 transmitter. My number one priority was adding "spot" capability. I ended up building another transmitter. The basic transmitter is listed in the 1940/5th edition of the Stancor Hamanual as the Stancor 10P. I eliminated the AM modulator section, added a PA keying/spotting switch between the oscillator and final stages, separate (regulated) B+ for the oscillator stage and, for safety, shunt fed the output coil/capacitor.
The PA keying/spotting switch serves a couple of uses. In normal mode both the oscillator and power amp stages are keyed. This allows break-in operation but some crystals will sound "chirpy" in this mode. In the "spot" position the oscillator runs all the time but the 6L6 stage is still keyed... Not good for break-in operation but some crystals sound better.
In order to minimize chirp the 6J5 oscillator should have a stable supply voltage . See here for an example.
I built my transmitter on an aluminum 7"x9"x2" chassis that I found at a swapmeet. As of December 2005 Antique Electronic Supply lists 6"x10"x2" chassis that should work. Look under "enclosures". Another chassis option is wooden slat construction. See photos at http://www.prismnet.com/~nielw/6v6 for a 1950 ARRL Handbook example. Lay four octal sockets out in a straight line ( xtal-V1-V2-coil ) supported by two pieces of wood slat spaced correctly to support all four sockets. As usual, remember that lethal voltages present and handle accordingly. Even with wooden slat construction, have a front panel. My front panel is a 7"x9" piece of masonite painted with black wrinkle paint.
| C1 | 50mmfd |
| C2, C3, C5, C7 | .002mfd |
| C4 | 250mmfd |
| C6 | .01mfd |
| C8 | 300mmfd |
| C9 | .002 1000Volt |
| R1 | 25K |
| R2 | 1K |
| R3 | 100K |
| R5 | 25K 10Watt |
| L1 | 80 - 27.5 turns on 1.75" x 2.75" coil form 40 - 18.8 turns on 1.75" x 2.75" coil form |
| L2 | 80 - 6 turns on top of grounded end of L1 40 - 3 turns on top of grounded end of L1 |
| RFC1, RCF2 | 2.5mH |
| XTAL | Crystal, Fundamental freq |
| SW | DPDT Spotting Sw |
| K | Key |
| M | 100mA Meter |
| V1 | 6J5 |
| V2 | 6L6 |
Construction was fairly straightforward and designed to match my receiver.
For more about this transmitter see my 6J6/6L6 blog entry
here.
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