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[Amps] Alpha 77D anode choke swap?

To: <>
Subject: [Amps] Alpha 77D anode choke swap?
From: "Jim Thomson" <>
Date: Sun, 22 Apr 2018 06:40:29 -0700
List-post: <>
Date: Tue, 17 Apr 2018 17:00:47 +0700
From: Martin Sole <>
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?

<Martin, HS0ZED

##  You could have moved  the 25 mhz  resonance  up to 26-27 mhz, simply by 
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. 

Jim   VE7RF     

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