[Collins] 32V-2 Help

[Gerald]

On Tue, 2005-06-28 at 09:34 -0400, Jim Walker wrote:
> I am in the process of working on a 32V-2 transmitter.  I have two
> problems that I have yet to get a handle on and would appreciate help.
> The first is on 15 meters the transmitter will not load on 21.6 (the
> multiplier alignment frequency).  I get a dramatic dip but no power on
> the BIRD and dummy load and it looks more like parasitic oscillation.
> This is in the #6 loading position.  If I go to the low end of 15 meters
> (21.0 - 21.4) I can get good power but the higher in the band I go the
> less power and more prone to have the loading act very squirrelly.

I'll go out on a limb. I am not intimately familiar with any 32V
transmitter, I've never seen the schematic but I have seen one or more
32V in person.

It does take reducing the loading capacitance when going higher in
frequency. It may be that you need only to go to the next load switch
position if there is one or set the variable loading capacitor for
greater loading at 21.6 MHz. A PA that is lightly loaded is most prone
to parasitic oscillations, but often good loading cures them.

It may be necessary to check the neutralization on 10 and 15 meters to
keep the PA calm. Its possible that some parts that may look like
bypasses are actually part of the neutralization bridge and they may
have drifted too far.

> Since all of the other bands behave correctly with good power and
> stability including 10 meters.  I changed the three mica capacitors in
> the multiplier stage that are associated with 15 meters on the
> assumption there was a multiplier problem. I replaced them with silver
> mica 500 volt capacitors.  While more stable, the problem still
> persists.  Am I correct in thinking the transmitter should load the
> range from 21.0 to 21.6?  Any idea on where to go next?
>  
> The second problem is the CW side tone oscillator produces a raspy buzz
> when the transmitter is keyed in the CW mode and using a 600 ohm
> military speaker on pin 16 and ground according to the manual.  I also
> tried a 600 ohm headphone element but had the same result.  In AM I get
> good audio reports so the problem appears to be in the CW side tone
> oscillator circuit V205.  I have checked the original tube and found no
> problem and ultimately replaced the tube.  I have replaced the three
> mica .01 capacitors (C208, C209 and C202)  with SPRAGUE orange drops with
> no change in the CW side tone.  The four RF chokes L201 - L204 check
> good.  Any ideas on where to go next on this one?  Thanks, Jim KZ5AW

Check the supply to that sidetone oscillator for ripple. Try a .01
or .05 disk ceramic across the tone output terminals to keep RF out.
Check the resistors (with three equal value capacitors it sounds like
the circuit is that of a phase shift oscillator). If the resistors have
drastically changed value the tube could be getting more feedback
voltage than it needs for a clean sinewave and so be making the sawtooth
buzzy sound.

I don't know that the sidetone should be a clean sinewave. A relaxation
oscillator does give a buzzy raspy sound but starts far quicker than
most sinewave oscillators when keyed.

You say the RF chokes check good? Have you removed them from the circuit
and checked for inductance and Q or have you just checked to see they
show continuity?

-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer