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[AMPS] Plate choke

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Subject: [AMPS] Plate choke
From: wes@Iphase.COM (Wes Atchison)
Date: Mon, 30 Mar 1998 09:19:37 -0600
At 02:09 PM 3/27/98 EST, km1h @ wrote:
>On Fri, 27 Mar 1998 13:41:29 -0500 (EST) (Paul
>Hrivnak) writes:
>>        The choke cofiguration I used when I was at Drake in 1995 when 
>>did the new L85 single tube 3-500Z ( now cancelled ) is as follows
>>(1) 1" dia x 6" ceramic steatite form unglazed
>>(2) wound with #22 nypol magnet wire for a total of 110 turns. There 
>>was a
>>split silver plated slip ring in the middle of the choke at 55 
>>essentially I had two 55 turn windings on the form connected in 
>>series. The
>>ring was used for a soldering point.
>>(3) Soldered a 50pf 10Kv disc, HT57 or equivalent capacitor between 
>>TOP(tube connection) and the middle of the winding. This cap must be 
>>high quality and capable of high currents and dissapation capability. 
>>disc cap was 1" dia and 3/8" thick with leads mounted at 180 degrees
>>apart.( This was a custom made unit )
>>(4) This placed the resonance of the choke at 5.5Mhz (gap between 
>>(5) Coated the choke with dielectric varnish etc
>>(6) In line choke for 160 meters in series with the plate choke, 1/2" 
>>dia x
>>2 1/2" long with 30 turns for the first layer and another 30 turns for 
>>second layer wound on top in the reverse direction.
>>        We did not try this at power levels more than 1000watts , but
>>worked very well for all the bands from 1.8 to 29.7 Mhz for a single 
>>running at 3400vdc. This was exhaustively tested with the usual 3 100 
>>watt metal film resistors wound with 4 turns #16 tinplated buss wire 
>>the vhf suppressor. We also used 4 different new tubes with the same
>>                                Regards  Paul
>>Bramco Palstar Inc.
>>Piqua, OH  45356
>Sounds like a lot of work and expense for just a single 3-500Z  amp IMO.
>Why not just copy the AL-80A/SB-1000 design and be done with it? They DO
>work in case you were not aware of it. 
>Or is there Engineering Revenue involved here?
>Sometimes it does not pay to re-invent the wheel. It is also a shame that
>Drake found themselves priced out of the market...again.
>I'm just wondering Paul, how many times are you going to flog that same
>basic single 3-500Z  design? Hammond,  Viewstar, AEA , Vectronics, Drake
>and I may have missed a few.
>Cheers  Carl  KM1H


I have been following this tread on Plate RFC's.  I have a single 3-500Z
amp made by AEA, now out of business, called a LA-30.  I may have missed
the design info on the RFC used in the AL-80A/SB-1000 amps.  Could you
expand on this or point me to where I can find the info on that RFC.

The problem I had with the amp originally was that it would not tune on
160m.  I found the loading cap needed to be increased. I added additional
fixed capacitance to the fixed cap in the circuit.  It now tunes.  

Then the RFC fried when tuning up on 10m.  I have wound several RFC's and
used a GDO to find the series resonances.  I now have a RFC that seems to
work except that a bypass cap at the base fo the RFC is getting HOT and
smokes on 160m.  The original circuit had a RFC would on a 3/4 inch rod,
nylon I think.  At the HV supply side of the RFC are two .003 uf caps to
ground.  Then a commerical RFC, I think a Z-50 type, in series with a .001
uf cap to gound.  The cap at the bottom of this stack up, the .001 uf, is
the one that smokes.

I assume the Z-50 type RFC is the second one refered to in some of the
mail.  With this circuit I do not understand why I should see enough RF to
heat up the cap.  

Any ideas as to what is going on?  Any suggestions as what I should do to
get the amp on the air?


CUL, 73's

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Wes Atchison                        FAX: 214-654-5586
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