Hello all AMers. I have started collecting and laying out parts for the homebrew 40 meter AM transceiver. I plan on using two 4d32 tubes modulated by four KT90 tubes.
The preliminary design goes like this.... Transmitter TX xtal osc: 5763 TX driver: 5763 Output: pair of 4D32 tubes Mike amp:12AX7 Tone control amp: 6EU7 Phase and driver: 12BH7 Output:PPP KT90 ........................... Receiver Osc/mixer: 6U8, or 6BH6 osc, 6BE6 mixer IF amps: two 6BA6 Detector: 6BJ8 S meter amp: 12AU7 BFO: 6BH6 The design will have an outboard power supply, variac between 0 and 1000 volts, separate adjustable screen supply with modulation choke, adjustable RF output bias, adjustable grid drive and grid leak resistance, no grid tuning, no antenna input tuning, xtal controlled rx and tx frequency. Controls will include: Mike gain, bass, treble, grid drive, grid leak resistance, bias voltage, screen voltage, screen resistance, rf gain, frequency select, bfo level, selectivity selection (4Kc and 5.5Kc). I am still not sure if I should include the mike amp and tone controls in the transceiver, or use the station setup like the other transmitters do, and eventually build a tube mike preamp/eq/compressor. Driving the grids of the KT90 tubes through a good hifi 8 ohm to 5000 ohm transformer would work very well, and enable me to playback recordings, use the good mike, and so on. On the other hand, building a good speech amp and using the D104 would be fun. I have a very good high voltage transformer, from Fair radio a long time ago, Collins, solder sealed, 550ma, a nice UTC cg choke, 500ma, 7000 volt CCS rated, nice oil filled caps, a nice 300 watt thordarson mod transformer, chassis, side supports, front panels, variac, pi net rf choke, caps, coil, etc. I need to get some high voltage brick diodes, two matching 4d32 tube sockets (I have 2 different kinds), the KT90 tubes, the receiver IF filter board, and a few other odds and ends. The rig should work well, 200 watts out at 600 volts, with about 200 watts of audio available at 600 volts, into a 300 watt mod transformer. Lots of current though, 400 to 440 ma on the final, 200 ma? on the modulator. Should I separate the power supplies for the rf and mod deck, with separate variacs? (I love knobs and meters) Brett N2DTS
