[Collins] Need help on a 32S-1 transmitter

[Gerald]

On Sat, 2005-11-05 at 07:33 -0600, David Murman wrote:
> I am in need of some technical help with a Collins 32S-1 transmitter that I
> purchased. The previous owner said he got excellent reports with it before
> he put it on the shelf. When I got the transmitter it was not working at
> all, had one tube that the filaments did not light and I had to replace a
> number of the tubes. After replacing the defective tubes I still got no
> power out.

I've had troubles with a transmitter regularly used of the bandswitch
contacts getting corroded. A few rapid bandswitch operations generally
cleaned them up. A quarter drop of DeoxIT on each contact with some
operation should clean that up.
> 
> Well I tuned up the transmitter on 3.6 MHz with my scope as per the manual
> and up to the final gird I have power but I see no grid current on the meter
> nor much power out ( about 1-2 watts). I noticed that I can peak the exciter
> tuning but when I dip the pa tuning the power to the input to the finals goes
> down. I do get a good dip but then again I only see about a 1 or 2 watts out
> and NO grid current. Rocking the pa tuning I see the power increase to the
> grid of the final.

It will take about 35 volts peak RF (70 volts peak to peak) on the PA
grid to get into grid current.

When tuning the PA plate changes the grid voltage it hints that the PA
neutralization is not right. Likely a trimmer problem as you've noticed
other trimmers with problems. If the trimmer moves, a quarter drop or
less of DeoxIT on the bottom center may clean up the trimmer to make it
work again without having to replace it.

> 
> Looking at the coil in the final area it looks like it was re-soldered. I
> don't have any idea if the taps are in the right area. I have attached a pic
> of the coil.

The reflector doesn't allow attachments.
> 
> Also the manual I downloaded from the Collins page is missing page 11 and 12
> and there is no good parts layout that I can find on the web.
> 
> Anyone have any ideas as to the issue with the grid current and PA loading
> not giving increases power when dipped? Also anyone have page 11 and 12 and
> any parts layout of this transmitter that they can send me?

What is the PA idling plate current? That can give several hints for the
drive and output problem. Low drive can come from tuned circuit
problems, which are affected by bandswitch and trimmer connection
problems or from a poor tube in the exciter chain or low voltage in the
driver plates. That could come from a bad rectifier in the power supply
or a bad choke or filter capacitor or poor relay contacts. Low output
can come from the PA screen being open which would be indicated by not
being able to get the idling current up to the rated value. Excess PA
bias could also keep idling current way down and RF output way low and
prevent seeing grid current. There are two jacks on the back connected
by an internal jumper that if that internal jumper is off (used for
transverter operation) the PA screen voltage will be zero giving very
low output, but grid current should be normal. Getting grid current
virtually depends on every stage of the transmitter so there's no
particular component to blame it on. Signal tracing with the wideband
scope is the only way to find loss of gain. A gang of weak tubes can
loose some gain each stage to make troubleshooting more difficult.
> 
> Would really like to get this transmitter working with my 75S-3.
> 
> 
> 
> Thanks;
> David
> WA4ECM
> 
One dips the plate current with the plate tuning and increases loading
by reducing the loading capacitor (turning the lever clockwise). One
doesn't dip with the loading control. Ignoring the plate current meter,
one alternately peaks output with loading and plate tuning controls.
They interact so it takes several adjustments of each to progressively
reach maximum output power.
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer