[Johnson] CHALLENGER STANDBY PLATE CURRENT

[Ed - K9EW]

Just a follow-up on my problem with 80mA of plate current when in the
STANDBY mode...

I checked C3 and C4, and they're both good.  I had already replaced C3 with
a 450v rating capacitor.

I substituted another 6AQ5 clamp tube, but no change.

The screen grids of the 6DQ6A's in the PA were reading 0V in the STANDBY
mode, but they were drawing 80mA of plate current.  I removed the tubes
just to be sure I was actually measuring plate current, and without the
tubes the current was zero.  I put the tubes back in, one at a time, and
with one tube I got 40mA of plate current in the STANDBY mode; with both
tubes in, I got 80mA.  Must be the tubes.

I replaced both tubes with others in my spare tube box and... that was it.
No more plate current in the STANDBY mode.  Normal operation in the other
switch positions.  I thought I'd ordered some new spares, but must have
used them somewhere else.  So I'll order another pair to put in the
Challenger.  The tubes I removed were the original Johnson-stamped tubes so
I guess it was time for a change.

Just wanted to let others know how this was resolved in case you start
drawing plate current in the STANDBY mode.

73,
ed - k9ew


On Tue, Dec 17, 2013 at 4:37 PM, Glen Zook <gzook at yahoo.com> wrote:

> Do you have a key plugged into the key jack?  The key jack shorts the
> cathodes to ground when there is not a key plugged in.  80 mA is not right!
>  It should be 0!
>
> If you have a key plugged in, and the key is open, then there are
> 2-capacitors that may be shorted.  The most likely is C-3, a 2 mfd
> capacitor.  The "modern" replacement will be 2.2 mfd.  Replace with at
> least the rated voltage on the capacitor and a higher voltage rating is
> better.
>
> The other capacitor is C-4, a .005 mfd capacitor.  The "modern"
> replacement will be 0.0047 mfd.
>
> Glen, K9STH
>
>
> Website: http://k9sth.com
>
>
>   On Tuesday, December 17, 2013 2:50 PM, Ed - K9EW <k9ew57 at gmail.com>
> wrote:
>  I just got my "new" Challenger set up for my winter station, and I have a
> question...
>
> The Plate Current is about 80mA with the Operate switch in the Standby
> position (Grid Current is zero).  Does that sound right?
>
> Thanks - ed, k9ew
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