[Johnson] Valiant Chirp suggestions

[Al Parker]

Hi Steve, et al,
    I was part of a fairly long thread on the problem a yr or so ago -- I'll 
paste the (maybe) conclusion of it here.  It might be difficult to figure 
out who says what, but --
------------------
----- Original Message ----- 
From: "Dave Maples" <dsmaples at comcast.net>
To: "Al Parker" <anchor at ec.rr.com>; "Old Tube Radios" 
<boatanchors at theporch.com>; "Johnson list" <Johnson at mailman.qth.net>
Sent: Wednesday, December 05, 2007 10:00 PM
Subject: RE: [Johnson] Re: Valiant chirp - fixed (long)


> Al: I have been chasing what I think is the same problem--VFO pulling--for
> years!  I don't mind pulling the transmitter and remounting the capacitor,
> but did W8JI indicate that anything about doing it was special?  If not,
> that sounds like the ticket.  While I'm in there I'm going to ground the
> exciter cap shaft as well...mine has always had an "issue", and now that I
> know how important that can be, I'll definitely give it the treatment.
>
> Dave WB4FUR
>
> -----Original Message-----
> From: Al Parker
> Sent: Wednesday, December 05, 2007 4:58 PM
> To: Old Tube Radios; Johnson list
> Subject: [Johnson] Re: Valiant chirp - fixed (long)
>
> Hi agn folks,
>    Well, I think I've made the cure, thanks to all.  I did get 3 responses
> from the BA list, and 2 from the Johnson list.  4, 2 from each list, said 
> it
> was 40m RF getting back into the VFO, which was operating on the output
> freq.
>    3 suggested fiddling the mechanical switch that changes the VFO freq.
> from 1.8mc to 7mc on 40m & higher freqs.  That would keep the VFO from
> operating on the output freq. exc. on 160m, where it doesn't seem to be a
> problem for anyone.
>    Tom, W8JI, correctly identified the actual cause of the problem by
> sniffing with a probe.  The final tuning capacitor, C8, is isolated from
> ground for some reason.  Usually a capacitor rotor and shaft is grounded.
> In this case the shaft, which is about 8" long, and goes thru the front
> panel to it's knob, picks up RF from the final tank coil which is
> conveniently close coupled to the capacitor rotor and shaft.  I quote 
> Tom's
> analysis here:
> -----------
> "I got out my H field probe and started sniffing around
> inside the cabinet and found all of the problematic current
> was coming from the shaft that runs back to the plate tuning
> capacitor in the PA tank. I measured almost 1/2 amp of RF
> current on that shaft on 40 meters in mine!! It was making
> the VFO shaft hot with RF."
> ------------
>    I made myself a crude but sensitive probe and also found a large amount
> of RF on the shaft.  I did as he did, with a long insulated screwdriver
> grounded the shaft - the frequency shifted slightly, and the chirp was 
> gone
> (maybe).  I say maybe because I my case once I had slid the chassis about
> 10" forward out of the cabinet, there was no chirp to be found.  Ain't 
> these
> things fun?  Anyway, to lengthen the story, I really didn't want to horse
> the thing all the way out of the cabinet and remount the capacitor to 
> ground
> it, as Tom had done.  If I had a strip of phosphor bronze I would have 
> made
> a grounding strip for the shaft to rub on, and mount it using existing
> hardware that would't require getting underneath.  I almost started making 
> a
> spring strip from a hacksaw blade, to mount a graphite motor brush on to 
> rub
> on the shaft & ground it.  But the motor brush pair nad a nice 3" long
> stranded copper wire, probably a bronze alloy.  So I cut it off, twisted 
> it
> arouond the 1/4" shaft 4 times, crimped the ends in a spade terminal and 
> put
> the spade under a VFO shield screw, with some "preload" to keep the coils
> tight on the shaft.  A cupla drops of DeOxit ProGold, and it checked out
> fine business with the RF probe, and even after going back in the cabinet.
> It may not be a long term permanent fix, but I think it'll do the job for
> many months.  I could have remounted the capacitor in less time, but just
> don't feel strong today.  I've horsed it around enough in the last month.
>    Thanks to all who helped.
> 73,
> Al, W8UT
----------------------
----- Original Message ----- 
From: <sbjohnston at aol.com>
To: <johnson at mailman.qth.net>
Sent: Sunday, September 14, 2008 10:34 AM
Subject: Re: [Johnson] Valiant Chirp suggestions


>
> I have a vague memory that someone reported that they had chirp on just 
> one band in a Ranger or Valiant, and the fix was to ground the metal shaft 
> of one of the controls (bandswitch?  VFO?  I just don't remember) with a 
> piece of flexible braid to the chassis.
>
> For chirp on all bands, I'd look to the sequential keying system.
>
> Steve WD8DAS
>
> sbjohnston at aol.com
> http://www.wd8das.net/