John,
It¡¯s not really pointless to adjust the 20 M coil, with L10 used exclusively for 20 M band resonance. ?There is a threshold inductance value that will cause oscillation: correct inductance is essential in this design. ?It is possible, if the coil is so far out of adjustment (or DC open-circuit in the winding), oscillation will not occur, confirmed with no grid leak bias. ?Consider noting the present position of the coil¡¯s adjustment screw, then experimentally adjust this coil, without going beyond the mechanical stops. ?You can always return to the present coil position if an adjustment doesn¡¯t help. ?But, yes, it sounds like point-to-point continuity checks and short-circuit isolation is in order, first. ?(I expect you have already done a close visual inspection.) ?Check the DC continuity through L10, from the junction (node) of C73 and C74 to ground, with the Band switch in the 20 M position; the capacitors should provide a good DC block to the remainder of the oscillator circuit, although you may see some capacitor charging. Then, switch to the 15 M band with the ohmmeter probes in these locations and confirm open circuit.
Do you know that the 18000.00 kHz crystals you have are series resonant, third overtone crystals? ?I have a Tedford Labs HC-6/U crystal in my radio ¡ª verifying, there are no markings on the container indicating parallel or series resonance, so I know of no way for you to confirm series resonance at this frequency, unless you have a dedicated test circuit.
If you haven¡¯t already, try lightly tapping on these dysfunctional crystals with a finger nail during in-circuit operational check: this may provide indication of an circuit connection problem within a crystal.
73,
Michael Smith, N4KZO
