Charles, you obviously are familiar with this transmitter. You don't happen to know where I can get a schematic, do you?
Joe On Fri, Jun 21, 2013 at 5:07 AM, Charles P. Steinmetz < [email protected]> wrote: > Joe wrote: > > I have an old AM transmitter that has three 6AL11 compactrons. The crystal >> is a fundamental, cut for 660 KHz. I don't have a schematic for this >> thing, >> but I believe that one half of one 6AL11 is used for the oscillator. >> > > The problem is, the frequency decreases as the rig warms up. It will >> eventually stabilize, but the final frequency is over 200 Hz low. >> > > It is an LPB RC-6A carrier current AM transmitter. >> > > The LPB 6AL11 transmitters use the pentode section of the tube as an > oscillator. There is a capacitive divider to ground from the screen, and > the crystal is connected from the midpoint of the divider to the grid. > There is a small capacitor from the grid to ground that tunes the crystal. > On some models, it is a selected mica cap in the neighborhood of 40-50pF. > On others, it is a ~33pF fixed mica in parallel with a ~30pf (max) mica > trimmer. > > You should be able to get it more or less on frequency unless the crystal > has aged too far, but it is always going to drift badly unless you redesign > it. > > Best regards, > > Charles > > > > > > ______________________________**_________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/** > mailman/listinfo/time-nuts<https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
