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Re: [Amps] AL82 pi network C2 failure

Subject: Re: [Amps] AL82 pi network C2 failure
From: Victor Rosenthal <>
Date: Thu, 9 Dec 2021 11:25:06 +0200
List-post: <>
It is possible to fix this. I had a similar problem with the loading capacitor in my TL922, due me stupidly operating with a high SWR ("I'll just finish the contest and then I'll fix the antenna").

First you file off the blobs with a needle file. Then you slide some emery paper of successively fine grit between the plates to polish them as much as you can. Probably you need to remove the capacitor to do a good job as I had to do.

Those capacitors don't give you a lot of headroom. Best to keep the SWR below about 1.8:1. Sometimes you can get away with it (for a while), but as you found out, it gets you in the end.

Victor, 4X6GP
Rehovot, Israel
CWops #5
Formerly K2VCO

On 08/12/2021 9:31, Robert W5AJ wrote:
Initial arc(s) occurred with the phased HF2V array on 80 meters (HF2V array
not used on 40)
Think a key is doesn't arc on other antennas/bands, initially.
first amp that failed output loading capacitor had Vacuum relaying on
output, reed relay on input.
wouldn't arc on other bands initially but over time, a blob/damage appears
on one of the capacitor plates, then it was pointless.
filing off bad parts was also futile fix.
Before capacitor plate was damaged, could run 1000watts out for a few
seconds before the capacitor would arc over.

AL82 has clanker relays for T/R switching.  My rig has a "TX DLY" which
delays RF by the setting (8ms) after KEY OUT jack closes.

After 1st amp failure, changed insulators on HF2V using longer distance
between AL sections but those those insulators show black marks (RTTY
Contest failure).  Replacement of insulators with some insulating material
is next but it's getting old....
oh, me too.
My guess is WX had some play in the insulators failure/arc.

failure is on loading variable capacitor.
since I'm going to be taking AL82 apart, anything else I should be looking
for while in there???

73 Robert W5AJ

I have met Death many times,
Someday Death will win

On Tue, Dec 7, 2021 at 8:30 PM Rob Atkinson<>  wrote:

My guess is that you are not sequencing your station, or you are, but
there's a timing problem.  When you run high power you have to have a
sequencer so everything that changes state can do so and pull in
before RF gets generated.   The idea is that for example, your
receivers mute, VFO comes on, receive preamps power down, antenna
change over happens, and any switching out at your antenna feedpoint
is done before the transmitter RF comes on.  Then when going to
receive, RF drops first, and everything else flips back over next.  It
seems like there's something hot switching, some relay maybe is a few
milliseconds too slow out at your antenna so for an instant, your
power amplifier sees an infinite impedance.   That will flash over
somewhere.  A vac. cap won't save a hot switched relay or contactor in
your system.  You need to delay your RF on make, and have it drop
first on break.

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