[Amps] Re: LK-500ZC...

[PAUL HEWITT]

I think the earlier post says he eliminated the tubes as the fault.  It
still exhibits symptoms of a cathode to ground short but could be outside
the tube.  I'd start checking the filament and B- lines for shorts to
ground, by-pass caps, feed-thru's, filament transformer, etc.  I'd also
re-check the "known good" tubes by removing one at a time, Murphy is a
tricky guy!!
GL, Paul


PAUL HEWITT
WD7S PRODUCTIONS
QRO HOMEBREW COMPONENTS
http://wd7s.home.att.net



----- Original Message -----
From: "Roy Koeppe" <royanjoy at ncn.net>
To: "Amps Reflector" <amps at contesting.com>
Sent: Friday, March 05, 2004 5:45 AM
Subject: [Amps] Re: LK-500ZC...


> Asked...
>
> "Serial number 4017.
>
> Symptom:  When A/C power switch is turned on, plate current is 325 MA
> and
> does not go to zero.
>
> Plate voltage is normal at 3200 volts DC.  Grid current meter goes
> negative; pinned to left side of meter.  Do not use QSK.
>
> Troubleshooting thus far:  Disconnected B+ line at power supply board.
> Power supply is OK.  Substituted two other known good 3-500Z tubes;
> tubes
> are OK.
>
> Measures 5.79 rather than 5.0 filament volts (T1).  Caps C24, C25, C22,
> C23 and C28 check OK.
>
> Should D2 the 1N3308 Zener Diode be suspect?  This component seems
> difficult to check.
>
> Request help to troubleshoot the above described symptom.
>
> Thanks,
>
> Bee, K4JLD"
>
> Bee, one or more of your tubes has an internal short between its grid
> and filament.
>
> 73,   Roy      K6XK/0        Iowa
>
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