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Re: [Amps] Plate Choke Values

To: <alexeban@gmail.com>, <gswynar@durham.net>, <amps@contesting.com>
Subject: Re: [Amps] Plate Choke Values
From: Alton McConnell <amcconnell3@hotmail.com>
Date: Thu, 5 Feb 2009 15:25:14 +0000
List-post: <amps@contesting.com">mailto:amps@contesting.com>
Hello Alex and Everyone:
 
You would'nt happen to have a schematic and maybe some photos of this type of 
plate choke arrangement with the tank circutiry also?
 
I am in the process of building a 4-1000 amp and have not decided on GG or 
tetrode/screen supply operation.  
 
I have not settled on the oputput network yet either.  I have a large roller 
inductor and two vacuum variables for the ouput (tank) network and I am quite 
aware of the plate choke issue.  At least one person has reported using relay 
switched plate chokes to make sure they can use their amps on all the bands.
 
I would be very interested in seeing various solutions especially involving a 
single 4-1000 tube.
 
Thanks,
 
Alton> From: alexeban@gmail.com> To: gswynar@durham.net; amps@contesting.com> 
Date: Thu, 5 Feb 2009 15:29:24 +0200> Subject: Re: [Amps] Plate Choke Values> > 
Merry meet you all:> Based on the past experience we had when working on high 
power transmitters> at Elisra :> The impedance of the choke should be about 5 
to 10 times the design load> impedance of the stage:> That calls for about 15 
kilo ohms for a typical 1kW amplifier> That would translate to about 1.3mH for 
1.8MHz operation.> The main issue however is the propensity for parasitic 
series resonances in> such large chokes: not only is it getting lower in 
frequency as the choke> get higher in value, it also gets more difficult to 
place it between> operating bands, that got quite crowded with the WARC bands 
in. > Our solution in the end was to switch over to series feed: band switched> 
coils , parallel tuning and link coupling for the output.> It's not so bad as 
it sounds: once set up, they're set forever and quite> wide band. You might 
need only one or two coils to cover 21 or even 18 MHz> to 30 MHz.> It seems 
it's easier to design and build such a tank circuit than a really> foolproof 
plate choke.> > Alex 4Z5KS> > -----Original Message-----> From: 
amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On> Behalf Of 
Eddy Swynar> Sent: Thursday, February 05, 2009 2:35 PM> To: 
amps@contesting.com> Subject: [Amps] Plate Choke Values> > Good Morning All,> > 
Am I missing something here...?> > Extensive research here into years & years 
of ARRL HANDBOOKS, Bill Orr> HANDBOOKS, and the internet have shed precious 
little light in the matter of> optimum / minimum values of inductance for plate 
chokes in the B+ leads of> our tube-type linear amplifiers.> > > Have a 
look-see yourself: in designs that feature amplifiers that only go as> low as 
3.5-MHz, you'll see chokes that range in value anywhere & everywhere> from 
200-uh, to 50-uh. On 160-meters, I've seen quoted values as high as> 1.0-mh., 
and others as low as 200-uh.> > Just what, exactly, is a "...minimum reactance" 
for a choke, on a given> frequency band, to do its job effectively, anyway...? 
> > I know confusion can creep in in the form of the self-destruction of these> 
parts if the hapless home brewer happens upon a band where there's> 
self-resonance in the choke...but that issue aside, is this all some matter> of 
"...by gosh & by golly black magic", or are there very real minimum> standards 
& parameters that we should adhere to...? And if so, where are> said standards 
published...?> > I certainly can't find them via "...the usual" routes --- but 
again, I must> be missing something here...> > ~73~ Eddy VE3CUI - VE3XZ> 
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