[Amps] Alpha 77D anode choke swap?
jim.thom at telus.net
Sun Apr 22 09:40:29 EDT 2018
Date: Tue, 17 Apr 2018 17:00:47 +0700
From: Martin Sole <hs0zed at gmail.com>
To: amps at contesting.com
Subject: Re: [Amps] Alpha 77D anode choke swap?
<You comment about the unconnected turns got me thinking and Jim
<commented on this as well.
<So I wrapped 3 turns of insulated solid wire, taken from some CAT5
<twisting the ends together so it's just a shorted but otherwise
<unconnected coil wound over the top of the plate rf choke.
<Testing with the W8JI light bulb method showed an initial bulb
<brightness peak (no gimmick coil) around 25Mhz, likely fireworks for 12m
<indeed. I tried a 4 turn coil first and it moved the resonance up to
<27.5Mhz, I thought that a bit close to 10m so I removed one of the turns
<making it a 3 turn shorted coil. Resonance peak, maximum bulb
<brightness, is now around 26.5Mhz. Is this the magic sauce?
<What am I missing? Is there going to be sufficient heat in the choke to
<melt the pvc insulation causing an almighty mess and associated fireworks?
## You could have moved the 25 mhz resonance up to 26-27 mhz, simply by removing
2-4 turns from the very top of the coil ! On the old B+W 800 plate chokes, which were
90 uh units, wound with 27 gauge, space wound magnet wire. Some times the choke burned up
when using 15M ssb. To move the resonance up a bit, 4 turns were removed from the top of the
coil...but back then we did not have a 12m band. Baffles me whey the B+W 800 resonated at the top end of
15M band, or just above . It was wound on a spiral wound grooved ceramic form, with space between adjacent
## Your shorted gimmick 3 turn coil works, but being that the 3 turn gimmick coil has its ends shorted, it might
result in high circulating currents inside the 3 turn coil. Just keep an eye on it, it should be ok. The advantage of
your gimmick coil is its dead simple, and no turns have to be removed.
## The W8JI light bulb method for testing for resonances works superb. Provided you have a supply of 12 vdc @
100 ma miniature light bulbs. This is no place for LEDS.
## I have my L4B in the shop in pieces right now, so cant verify 12 M operation of the plate choke. It does work
on 17M, that I can verify. Its a 154 uh choke.
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