[Johnson] switch

[John Lawson]

On Sun, 4 Mar 2007, TOWN COUNTRY FLOORS Owner wrote:

> Gentlemen,
>
> I just noticed that my ceramic switch wafer for the aux coupling switch on
> my Valiant has cracked in half.  Is this repairable with epoxy and if not
> are there replacements available and if there are where can I find one?

   Is it actually failing? Is it arcing over or not making contact?  If 
it's still 'working' - I'd be inclined to use it as little as possible 
(think twice about multi-band contest for a while... ;} ). Maybe wrap some 
lacing tape around the mounting screws to hold the wafer together.

   That switch carries heavy RF currents and voltages.   I would be leery 
of trying to repair it - especially with epoxy or (blasphemy!) JB Weld - 
unless the cracks are far away from the contacts, and the rotational 
stress won't tend to make it break again.

   It is also a non-standard contact arrangment - it 'adds' the coupling 
caps in parallel.  (300, 600, 900, and 1200 pF.) The schematic is 
poorly-drawn in that one has to infer (or inspect) the fact that the 
wipers are tied together internally. The Johnson part number is 22.1308 
(SW6). That and $3.50 will get you a coffee at Starbucks, too.

   If it fails entirely, and a 'parts donor' is not available - there is 
plenty of room right there under the chassis. I'd be tempted, in that 
case, to use four small SPST HV relays and a suitable switch to pick them 
in the correct sequence, using the existing hole in the panel and knob.

  Of course this makes the rig "less than stock" - but it gets you back on 
the air.  And, if you *do* subsequently find a switch, the mod can be 
reversed fairly easily - and no cosmetics or chassis mods will be 
required.


    Cheers

John
KB6SCO
DM09fg