[Hammarlund] Unstable Oscillator adjustments in the HQ-180

[Roy Morgan]

On Jan 31, 2016, at 7:45 PM, K3PID <Ron.K3PID at sbcglobal.net> wrote:

> It's not a drift problem! The VFO is rock stable after a short warm-up. I
> made the addition of the separate filament supply for V2 & V18. The problem
> ( or perceived problem ) is touchy transformer adjustments! 

Ron,

Some guesses:

1) The oscillator coil assembly is having a bout of “The Dreaded IF Can Silver Mica Capacitor Disease”.  The cap(s) in the base of the IF/Oscillator cans develop intermittent or definite short circuits. The cure is to route out the offending cap(s) and replace them with silver mica caps on the can connection studs.

My fuzzy schematic shows a separate oscillator coil can for each band - T23 through T27.  Is this trouble present on all bands?  There seems to be an inductance adjustment (slug in the core) and parallel trimmer for each band.  the fixed caps appear to be in series with the coil to ground and on one band is comprised of a feed cap and an NPO 750 temp compensating cap.  They are shown with various values and are shown external to the can, so the Dreaded Can Cap Disease may not be happening if they are actually not built into the base of each coil form.

2) The oscillator coil is somehow loose on the former in the can.  Motion of adjustment causes random changes in inductance.

3) There there is an intermittent connection at the coil winding/stud soldered joint.  (Clean varnish off litz wire by heating the wire strands against an aspirin tablet with the solder pencil.  Wash well. )

(Is there a clean, clear schematic online anywhere?)

Roy

Roy Morgan
k1lky68 at gmail.com
K1LKY Since 1958