[Hallicrafters] SX 101A Challenge

[Rocco Lardiere]

David,

I should have stated the obvious - I tried two other 12BY7A's.  One
produced identical warble.

With the third, the stage broke into a parasitic oscillation - sounded
like a repetitive chirp.  Possibly some kind of motorboating?

Also - the warbling occurs at all points on the dial. The tuning cap
looks perfect, and I have cleaned it, including the bearings.  The
tuning is absolutely smooth.

Rocco
"T. David Cohen" wrote:
> 
> Change the 12BY7...that fixed mine.
> 
> Good luck!
> 
> -----Original Message-----
> From: hallicrafters-admin at mailman.qth.net
> [mailto:hallicrafters-admin at mailman.qth.net] On Behalf Of Rocco Lardiere
> Sent: Friday, September 13, 2002 12:46 AM
> To: hallicrafters at mailman.qth.net
> Subject: [Hallicrafters] SX 101A Challenge
> 
> To the Hallicrafters Experts:
> 
> OK - I am stumped.  My SX 101A local osciallator is warbling slightly,
> and I can't stabilize it.  This is not the usual temperture drift.  This
> is a slight delta frequency, continuous, perhaps only back and forth a
> few cycles, but it is constant from turn on to whenever.  It just sounds
> awful on CW.  It is more pronounced at higher frequency bands.  The
> problem is in the 1st conversion oscillator - I can hear it clearly when
> I couple my test receiver to the tube and listen to it directly.
> 
> I have rebuilt and resoldered the components around V3, the 12By7A, and
> it is less prone to vibration now.  This problem is not related to
> vibration or turn on temperature changes.  The B+ and bias to the
> cathode look clean and stable.  The warble is not a steady beat note -
> it is just back and forth at a few hertz, but not at a stable low
> frequency.
> 
> I have tried tugging on every freq component, including the main
> variable cap.  I resoldered everything in sight.  Everything looks
> solid.
> 
> This is a really beautiful 101A - very, very clean, so I want to save
> it.  I suspect the receiver is like new because this problem has been
> there from very early in its life.
> 
> Any hints?
> 
> Rocco Lardiere N6KN
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