[Johnson] Bigger ain't better

Sun, 4 Jan 2004 16:10:33 -0700

Sounds like you replaced the series/parallel capacitor networks with
individual high voltage ceramic caps.
The caps are failing because their current ratings are being exceeded.
As I recall, these caps are in the input arm of the PI network.  The
series/parallel networks will fail when the tank circuit is not properly
dumping it's RF output to the antenna; like if you have bad antenna
changeover relay,  a bad solder joint at the output coax connector, or
failure of the loading caps.
The networks use the series/parallel arrangement to increase the current
carrying capacity of the mica capacitors.  Are the single ceramic
replacements able to handle the current under the normal circuit conditions?
Another thing to check is the loading switch wafer.  These contacts are
prone to intermittent failure.  I had to replace all the contacts on my
Valiant's loading switch wafer.  Almost all were intermittent.
Hope this helps.
73
Damon Raphael, W7MD
----- Original Message ----- 
From: "skip" <[email protected]>
To: <[email protected]>
Sent: Sunday, January 04, 2004 1:38 PM
Subject: [Johnson] Bigger ain't better


> Hello fellow  Johnsonites,
>
> I replaced my 330 and 150 uf cap in the Viking Valiant today and they
still
> heat up.  I used A2 type ceramic 5000v units.
>
> I don't believe that the cap's are the problem.  Maybe I'm in the dark,
but
> the clamp tube 6AQ5 doesn't seem to be warm.  The filaments are lit.  Like
> the lights on but nobody's home.
>
> Just before the cap's smokes the plate current went full scale.  This
could
> be from the cap shorting out.
>
> When it works the reports are great, full audio and solid carrier.  I have
> only used it on 80 mtrs with a SWR of 1.2:1 and top of phone band  at
1.7:1
>
> Any hints ?????  No tubes get hot or red plates.
>
> tnx  de Skip    K3CC
>
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