Fw: [Johnson] Valiant Chirp suggestions

[Al Parker]

sorry if you've seen this b4, I got a strange bounce msg from qth.net.
73,
Al
----- Original Message ----- 
From: "Al Parker" <anchor at ec.rr.com>
To: <johnson at mailman.qth.net>; <sbjohnston at aol.com>
Sent: Sunday, September 14, 2008 1:04 PM
Subject: Re: [Johnson] Valiant Chirp suggestions


> 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/
>
>
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