[Amps] Alpha 77Dx two hole

[Paul Christensen]

>"There is one immediate problem that I could use some advice on. The vacuum variable binds hard and stops well before reaching minimum capacitance.
This prevents operation on 20 meters and above.   have heard that it could be a dried great problem.  Any tricks to get free it up or am I in for a teardown?

First, check to ensure that the Jennings vacuum variable limit screw isn’t the problem, especially if you cannot crank a full number of turns.  My 77Dx's TUNE cap has exactly 29 turns from C-Max to C-Min.  I've seen this prevent 10M operation on more than one 77Dx amp.  Minimum capacitance on the Jennings vacuum variable cap is set with a small, slotted machine screw located near the 1/4-inch tuning shaft.  You must remove the front panel to access it:

1) Remove AC power cord;
2) Ensure HV is at zero volts, then remove the top cover;
3) Temporarily place a safety short on the HV+ line to chassis ground or B-;
4) Remove the front panel LOAD and BAND knobs with a hex/Allen wrench;
5) The TUNE turns-counter knob and plate are NOT removed.  The back of the turns counter is simply press-fitted against a Nylon Oldham coupling joint;
6) Remove all six (6) front panel 10-32 screws;
7) Now, the only thing holding the panel on are two Molex connectors.  Unplug the 15-pin and 6-pin Molex connectors near the top of the amp;
8) The panel comes right out and exposes the chain linkages as well as the vacuum cap travel set screw.  Be careful NOT to disturb the Nylon coupling joint on the TUNE capacitor shaft;  
9) Turn the vacuum cap limit screw counterclockwise to remove the limit.  As I recall, it may be possible to remove it altogether; its primary purpose was to limit minimum C to prevent 10-11M operation.

Paul, W9AC