[Amps] 500 uh plate choke

Vic K2VCO k2vco.vic at gmail.com
Tue Jan 22 16:16:10 EST 2013

I have several large pie-wound chokes, most around 1 mh or more. The thing about this one 
is that they found no series resonances below 100 mHz. It seemed to me that 500 uh would 
work well on 160m.
I have used the RFP chokes, which I think are about 225 uh. This is about 2500 ohms 
reactance at 1.8 mHz, which most likely makes the choke part of the tank circuit. My 
feeling is that this detracts from efficiency on 160, because the choke is a low-Q device.

On 1/22/2013 12:59 PM, Carl wrote:
> Pi stands for pie Rob, resembles a pie plate.
> In the "old days" the RF tanks were series fed so there was no concern about resonances 
> and a lot of inductance was used.
> Carl
> KM1H
> ----- Original Message ----- From: "Rob Atkinson" <ranchorobbo at gmail.com>
> To: <k2vco.vic at gmail.com>
> Cc: "Amps reflector" <amps at contesting.com>
> Sent: Monday, January 21, 2013 7:46 AM
> Subject: Re: [Amps] 500 uh plate choke
>> That's a pi wound choke (I'd like to know why it is called that).  I
>> usually see them in older ham AM rigs where the B+ is 1.5 KV or less
>> and the Ip is no more than a few hundred ma.
>> I am not saying it won't work in a modern RF power amp but all of the
>> ones on the market today seem to use some sort of solenoidal wound
>> choke.  Maybe that design is no longer manufactured in quantity?   I
>> think they can't handle much more than 200 or 300 ma.
>> I'd count the number of pi sections and look for a similar one at
>> hamfests.  If you want something like 800 ma Ip and 3 KV Ep you are
>> probably going to have to go with a solenoidal choke but I think you
>> can achieve 500 uH with one.  Actually that RFC-4L choke is lower than
>> I'd expect.  Most pi wound chokes I've seen are up over 1 mH, maybe
>> even 2 1/2 mH.
>> Rob
>> K5UJ
>> On Sat, Jan 19, 2013 at 1:44 PM, Vic, K2VCO <k2vco.vic at gmail.com> wrote:
>>> This site
>>> http://www.granta.g4axx.com/Linear_design_notes.php3
>>> mentions a 500 uh plate choke specified as RF Parts no. RFC-4L. They tested
>>> it and report that it has no series resonances between 1 and 100 mHz! RF
>>> parts doesn't list this choke anymore. I would like to obtain such a choke
>>> -- does anyone know if it is manufactured and if so who sells it?
>>> Yes, it sounds too good to be true, but the site is very authoritative. They
>>> mounted the choke in a box and used a vna to check it.
>>> -- 
>>> Vic, K2VCO
>>> Fresno CA
>>> http://www.qsl.net/k2vco/
>>> _______________________________________________
>>> Amps mailing list
>>> Amps at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
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Vic, K2VCO
Fresno CA

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