I'm deciding on what circuit I'll use, based on recent measurements, for a CW receiver for 3500-3650KC, built 60 years late (as was 8PV4) but for fun. Specs wanted: * 3.50 - 3.65MC with no drift after 1 hour warm up * Circuitry to fit 12 X 5" chassis, with front panel of 5 X 8" (8PV4 XMIT mate) * Narrow selectivity as for tight CW only, covering only CW sub-band. * only the gain needed for Y2K conditions, using full size dipole (50uv). * to run on +250V, 105V and 6.3V and give 100mw to 800mw AF output. To meet all those specs, using the 470KC CW crystal filter mentioned earlier, I may have to use a circuit as shown (tentative plan) in the pix, which has its oddities: * the 6SN7 works as Grounded Grid RF amp (which gives plenty of gain for Y2K use) and as audio output amp. * The 6SQ7 works as push pull detector (diode version of the Wunderlich detector) and BFO. * C202 adjusts BFO injection which determines at what point over-strong signals naturally get weaker in loudness (as they over ride BFO). that forms a sort of AVC action which will be good enough for CW (distortion not important). But as signal gets so strong as to grossly over ride BFO, a negative voltage will then be sent to V5, 6SG7 and so cut its gain. This will prevent being blasted. V3, 6SG7 might also get this voltage too, as AGC volts (see dotted line circuit). Experiments will tell what changes are needed, so the open-sides chassis will make it easy to make those changes. C1's tuning dial will likely be dial cord and pulley. So the front panel will be held away from chassis by 1/2" to fit pulley, dial cord and drive shafts between and give 2 support points for each. Since receiver will always by tuned to same frequency as the crystal controlled transmitter (8PV4, described earlier) the dial need not be micro precise in action or readout, just easy to zero in on signal with. Unlike the ARC-5 receivers, this will be CW only - no AM or MCW (nor SSB) so many things will be preset, not using controls; thus few knobs and levers on front panel: TUNING (FREQUENCY) and VOL (LOUDNESS) in this version. In all versions of receiver to fill those specs, all will be rather similar, use and function-wise, thus front-panel-wise. Much of final design choice depends on parts I have, can get and ability to do metal work the way I must do it now. ----------------------------------------------------------------- Another design being considered: 8PV6 has one more tube, which will be the 6AC7 HFO, replacing 6SA7s function as OSC/MIX, making it be just a MIXER and having an audio derived AGC (audio is rectified and used to cut back gain when signal is strong). C201 BFO injection cap is set so loudness rises (at 1st) with an increase in a weak signal, with jumper JJ1, open circuit. C201 then must be a bit larger than usual. But if too small, a strong signal will actually be less in loudness - except for the keying thump - and so fool the AGC into not working. In 8PV5 the BFO injection cap is set to a low value so only weakest signal is loudest. As signal rises in strength it over rides BFO strength and sounds weaker (except for the thump) - acting as if AGC'd until so strong that the rectified I.F. cuts gain via its biasing of 1st audio tube 6SG7. 8PV6 is a lot different then.