Date: Fri, 4 Mar 2016 19:34:07 +0100
From: Patrick EGLOFF <email@example.com>
To: "firstname.lastname@example.org" <email@example.com>
Subject: [Amps] HL2K high input SWR on 21 MHz
I have a HL2K amplifier (pair of 3-500Z) for several years now (got it
second hand) and it always had a high input SWR on 21 MHz. I matched it
with my TS850 antenna tuner, so it was OK.
During last contest i had a problem on 40m (500pF/2kV in output tank
shorted). So i had to open the amplifier and while being there i wanted to
see what's wrong with this SWR.
I couldn't reduce the SWR in adjusting the capacitor.
I removed all components used in the input tank and checked them. They are
Coil is 0.34uH and caps are as marked and on diagram.. Input C = 150 pF and
output adjustable up to 200 pF.
So now, i'm stucked....
On all other bands, the input SWR is just fine, so i suppose there is no
problem with the tubes or anything else in the amp. I have full power and
everything is stable.
Does anyone have a HL2K and can confirm that it is OK (or not) on 15m ?
Any idea on what could be wrong ?
Patrick Egloff - TK5EP
email : firstname.lastname@example.org
Web page : http://www.egloff.eu
## Did you actually check the tuned input coil, and the 150 pf fixed cap and
adjustable cap with a digital LCR Meter ??
My drake L4B also uses a pair of 3-500Zs, and the caps are both fixed.
The coil is adjustable....slug tuned. Input swr is 1:1 across the 15m band.
## The L4B uses paralleled 100 pf caps ( total = 200 pf) on the xcvr
and paralleled 65 pf caps ( total = 130 pf) on the cathode side.
## I suspect that either your fixed 150 pf cap is out of spec, or your fixed
coil is out of spec. Two paralleled 75 pf caps ( total = 150 pf) will
handle more RF
current vs a single 150 pf cap. Your 150 pf cap may well have been out of
spec since day
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