While I'm waiting on a few big tubes (another 805 and Two 811s) to arrive which will let me Heising modulate my big homebrew Xmitr, I decided to build a small low power (est. 3 to 5 watts) AM rig.
Tube lineup is all 1920s Cossor brand: 215HL for audio preamp (xformer coupled input), 220PT Pentode for Heising modulator, 220P Power Triode for oscillator.
I can push it up to 200V on B+ but I'm better off running the tubes towards their max rated voltage (150V).
It currently tunes across the entire 80m band and modulation can approach 100% if I keep the Osc. grid current down (black knob next to the right-hand varicap is the gridleak adjustment for this purpose).
The left-hand varicap is for antenna coupling and a small lamp to tell me when antenna line current is peaked. Frequency stability is surprisingly good, though it will vary as I load it up of course.
I'll try it over the next several days and see if I can make any local contacts while I'm waiting on the big tubes.
73s
geo
VE3GZB
