[MRCA] MAK oscillator continued

[Ray Fantini]

Additional information on the MAK issue. As per Mr. Smith's suggestion I did try running the transmitter on reduced voltages on some of the other channels that still have the original rocks. On both 3.000 and 3.155 the oscillator and transmitter work without issue all the way down to 10.5 volts. There is reduced output but the oscillator starts every time without issues so it appears that the original huge crystals have something that allows them to work at the reduced voltage where the modern crystal won't do it.
I like the idea of maybe trying a lower frequency crystal like something on 1.9425 that would have a second harmonic on 3.885 but would have to order a crystal. Perhaps another option may be to build up a small solid state oscillator that can plug into the crystal socket and treat the 12A6 as a buffer amplifier? I can steal twelve volts from the filament string and use that to power the oscillator but this involves building an external component that would fit in the radio and not be period correct. The other issue would be the oscillator can only be on during transmit because if its running during receive that will be a problem.
In a perfect world would hold out for something like one of the rocks that's used in something like a BC-669 or other huge rock to stuff in the transmitter but somehow think anyone who has something like that would not be willing to part with it so may try bread boarding a solid state oscillator and trying that or maybe look at the addition of a small trimmer between the plate and grid just to see how that goes but want to avoid frying the one crystal I have for 3.885 unless absolutely necessary.
Can always look at doing something different for the power supply but the solid state inverter that I am using now is an old Heathkit mobile power supply and the B+ section originally used a half wave doubler to get 250 or 275 VDC depending on how you taped the transformer. I modified the power supply to a full wave without the voltage doubler and that's where I am getting the 150 volts for the B+ On radios this old I find it hard to run full B+ or over and feel much better running ten or fifteen percent below the original value.

Ray F/KA3EKH



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