The AM Forum

I have a 32V3 that has a noticable chirp on CW.  It has a new tube in the PTO, new VR tubes and all other tubes checked or replaced.  The LV transformer is a Dahl replacement.  Any hints or do they all chirp a little?

You may have read this, if so please disregard:
https://wireless-girl.com/Projects/AMTransmitters/Collins32V.html

I've been running a 32V-1 this year on 80, 75, and 40 meters and agree with the observations.

A quote from the article:
"Third, the CW keying waveform has ringing and variations in it. The HV power supply has a resonating capacitor across the swinging choke to improve regulation. It works OK on AM, as the load is more constant. The transients caused by full power to no power input on CW are more than the circuit can compensate for. W8JI has some discussion of the resonating capacitor for another radio, but the material is applicable to the 32V. Most folks have a 32V for AM operation anyway. I did not ever attempt a fix for this. It looks real ugly on a monitor scope, but does not seem to generate many complaints from listeners on CW. Maybe not a big deal....."

I would keep an eye on the choke tuning capacitor. Mine developed a slow leak around the seal. The oil-filled cap is mounted on its side. It eventually turned into a smoke generator requiring replacement!

another Doug,
W3DBB

Hi All,

   The Late Patrick Turner of Turner Audio in Australia wrote in depth on resonating filter chokes in power supplies.

His old web site for now lives on being hosted by others.

Here is his take on resonate chokes in a power supply:

https://atrad-audio.co.nz/turneraudio/www.turneraudio.com.au/audiofilterchokes-page2.html

In short, one way to alleviate the sharp resonant peak as the choke inductance varies with DC current, is to lower the Q of the circuit by adding a series resistor with the capacitor.

Use something like 1X to 4X the DC resistance of the filter choke, and make it capable of getting warm, maybe 5 to 10 watt rated to be safe.

Jim
Wd5JKO

I had a 32V-3 for a number of years. I don't recall that it had chirp. I did some audio chain mods and solid-stated the power supply and put in larger filter capacitors.  This really increased the PEP on AM and then I had FM'ing of the VFO. I added 0.01 uf's across the VR tubes, and filament bus, and that solved the FM'ing for me.

What band(s) does this occur on?

Thanks everyone. I will check that resonating cap and perhaps add a series resistor.  The chirp comes from the pto so it is there on all bands.  The rig does work great on AM