I would very much like to recommend a grounded grid arrangement. I am using
one myself for quite a while now. I inherited it from the late 4X1AT, a very
nice ham. We were very sorry when he passed away.
The amplifier follows very closely the schematic from Will Orr, with a very
special power supply. The gentleman was a transformer wizard and designed
his own transformer.
If there is interest, I can scan the page and send it to you.
The link coupled unit is from an old QST and I can scan that too, at least
for information
Alex 4Z5KS
"Jesus, come get your kids, they're tearing up my Mother's backyard!"
_____
From: Alton McConnell [mailto:amcconnell3@hotmail.com]
Sent: Thursday, February 05, 2009 5:25 PM
To: alexeban@gmail.com; gswynar@durham.net; amps@contesting.com
Subject: RE: [Amps] Plate Choke Values
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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