[Central-Electronics] The Case of the 100V Audio Filter

[JAMES D COMSTOCK]

Yes, I have monitored the in and out. As I recall there was a small reduction in signal when going through the filter.
 I also used the radio for a while with a bench type solid state adjustable filter plugged into the socket. 
 I also wanted to mention that I had cleaned the socket with de-oxit and a brush several times.
 I made the wire brush for the socket contacts by using a hammer to fray the end of a piece of 3/32 stainless wire rope. 
 I am not sure, but I think taking the wire brush to the socket was the cure. 
 The 100v is my main radio and is used daily. I have been using it since 1971. Jim kojjf
  
> On 01/05/2021 1:22 PM Curt Nixon <radio.ku8l at gmail.com> wrote:
> 
>  
> WOnder if you have monitored the output of the filter in situ while it 
> is operating?  Might tell you something.
> 
> I like the socket possibility also.
> 
> Curt
> KU8L
> 
> On 1/5/2021 3:03 PM, JAMES D COMSTOCK wrote:
> >   Last time I had a similar problem with my 100v I gave up and completely rebuilt the filter with all new components. It worked for a while.
> >   Eventually I ended up running a tiny steel brush through the socket connectors and cleaned, tightened and re-soldered all the connections. The problem has not returned. If it does I will replace the socket.   Jim K0jjf
> >
> >
> >
> >> On 01/05/2021 10:47 AM Robert Nickels <ranickels at gmail.com> wrote:
> >>
> >>   
> >> I can toss out a mystery for the group to ponder:
> >>
> >> I've been trying to find the reason why the output power of my 100V is
> >> low.  Sometimes it would start out OK at 100 watts but then dropped to
> >> 60 watts or less a half hour or so later.
> >>
> >> I've narrowed the problem to the Audio Filter module but it's puzzling
> >> because I can't find anything wrong with it.    If I bypass it by
> >> jumpering  pin 2-5 so the phasing system is driven directly from the
> >> output of the Audio Limiter module, I can get full 100 watt output with
> >> 2.25 volts peak-to-peak out of the limiter.    The output of the filter
> >> is about 1/2 that level and the waveform becomes distorted as audio
> >> level is increased.   If I adjust the audio input to provide that same
> >> 2.25 volts out of the limiter with the filter in place the transmitter
> >> power output is only 30 watts.   Even if I increase the audio level
> >> greatly the output never gets to 100 watts.
> >>
> >> This makes it seem that the Audio Filter is defective, but I've run the
> >> module on the bench for hours, sweeping from 100 to 5000 Hz and it works
> >> perfectly.    The voltages in the transmitter are correct (6.5VAC fils
> >> and 315 VDC) but instead of the nice sine waves and consistent output
> >> within the filter bandpass I see on the bench, the output becomes
> >> distorted and triangle wave shaped as the level is increased, and will
> >> not drive the transmitter to full output even then.
> >>
> >> The next stage in the 100V is the phase inverter which presents high
> >> impedances so it can't be a loading effect, besides the limiter will
> >> drive this stage just fine.
> >>
> >> I'd like to have the audio filter inline but am getting nowhere in
> >> figuring out why it works on the bench but not in the transmitter and am
> >> about ready to bypass it and call it good. Wonder if anyone has run into
> >> this mystery before or has any suggestions?
> >>
> >> 73, Bob W9RAN
> >>
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