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[Amps] HV Diodes

To: <>
Subject: [Amps] HV Diodes
From: "Jim Thomson" <>
Date: Sat, 18 Oct 2014 06:11:47 -0700
List-post: <">>
Date: Fri, 17 Oct 2014 12:06:07 -0400
From: "Carl" <>
To: "Glen Zook" <>
Subject: Re: [Amps] HV Diodes

##  The .25 inch od roller used in the 8k is nothing to write home about.
Its really too small for 20-10m.    Its good  for 160-30m.    It really needs
.375 inch od tubing for 20-15m..and bigger still for 10-12m. 
The roller in the 8k use 21 air holes in the chassis below the coil. 
3 x rows of 7 holes.   They used the wrong blower in the 8 k.
Its way too small for 5 kw output. They used a single dayton blower,
which doesn’t put out any pressure.   The chimney is way too small in
diameter, and too much restriction at the base for airflow.   Then they lose a 
of air through those 21 large diam holes in the chassis...used to cool
the .25 inch tubing roller. 

##  I have several .25 inch tubing type roller inductors...and all of em are
a pita.  The entire coil has turns which are on a slight angle.   Think one
big spiral.   The pulley that rides on the  outside edge of the tubing, also 
has to be at
a slight angle.   Problem is, the pulley rides back and forth on a solid shaft, 
and that shaft
is straight as a pin.  To get the pulley to be on a slight angle, to match the 
pitch of the
coil, the hole in the middle of the pulley has to be slightly larger, so it has 
some slop to
it, and can be at an angle.   That alone is what causes the intermittent 
And right when u go to rvs direction, it has a ton of slop in it. 

##  I gave up on em, and tossed the pulley assy away, and used the remaining 
as plane coil stock.  Mine had insulators running the entire length of the 
coil, every 90
degs, 4 in all...and all on the inside.  Then the heavy duty insulated end 

##  I ended up using it, mounted vertical, as the 160m coil on the YC-243 amp.  
.375 inch tubing for 80+40m... then .5 inch tubing for  20-17-15m.  
Bandswitched the entire 
mess with a triple wafer model 88 switch.   No 10+ 12m on that amp, as I have 
no interest
in those bands.   A simople bandswitch is a helluva lot faster than a roller.  
Then the vac tune
+ load caps...with turns counters.   Makes for a fast band change.  Just dial 
up the various pre-sets
on the turns counters. 

##  Bottom line is, tubing type rollers are a major pita.   A lot of edge wound 
ribbon types are 
not designed good either.  However, a lot are a good design.   Notice how a 
roller is always de-rated 
for current vs  coil stock using the same size tubing or ribbon. 

Jim  VE7RF

At that low power level that size roller is usually adequate but the moving 
parts wear and create intermitents. They become a maintenance headache for 
some owners.

Its a cute little amp but it really needs a separate grid meter for those 
fragile tubes.

For real power the one used in the Henry 8K is needed and even then they act 

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