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Re: [Amps] Questions about Amps/Tubes/Design

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Subject: Re: [Amps] Questions about Amps/Tubes/Design
From: "Gary Hinson" <>
Date: Sun, 16 Mar 2008 12:59:02 +1300
List-post: <">>
> Amp Supply. The LK-500 had several models and every model had its own 
> production changes. Weak link is the bandswitch configuration 
> that allows it 
> to arc to the support hardware. Easy fix if you do it before 
> it happens.

I'd be interested to know more about that.  More below.

My LK550 is still going but not quite perfectly.  Maintenance/repairs so far
have involved:

- New set of HV supply smoothing caps and load-sharing resistors, not long
after I got it (about 1995?)

- 2 or 3 replacement Jennings vacuum output relays (I guess the QSK circuit
doesn't stop mine hot-switching: I use semi-QSK now)

- At least 3 new power switches (no slow-start installed so the PD HT
transformer thuds at switch on - that's another "one day" project!)

- Popped a padder cap in the output tuning on 160m (changed 5 paralleled
100pF HV RF ceramics, I think)

- New valves, one due to a heater short caused by heavy-handed removal
people, others to restore full output after a good decade of use

- Recently popped a bypass cap in the anode compartment (swapped a bunch of
bypasses and couplers while I was in there - figured they are getting old)

The LK550 has 3 x 3-500s and would need about 150W of drive, I guess, for
full output.  My little old TS850s can't get close, and to be honest I don't
like to thrash the gear so that plus the 500W license limit here ensures I
get long life out of the valves  :-)

Currently I'm having trouble tuning the amp on 80m (plate and tune controls
both max out - I've changed the padder caps for 80 but that didn't help, so
now I suspect the bandswitch) and a weird problem on topband (output starts
at 100W and takes about 5 secs to 'warm up' - no idea what's happening

Any clues on solving the current problems would be much appreciated.

Gary  ZL2iFB

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