[Amps] Plate Choke Values

[Carl]

In the old days of Class C and early SSB a 10X reactance was the norm 
for the choke.

As bands were added (15M took out the National R-175 for example and 
resulted in the R-175A) and since the late 60's the reactance went down 
to the 3-5X range. In those cases the choke actually becomes part of the 
tank circuit. You cant go by the calculated reactance either as 
distributed and stray C changes things in the real world. Sweep any of 
the modern chokes and you will see how close to smoke many are on a band 
or three.

You then wind up with having to install sufficient C as the choke bypass 
as electrolytics really object to RF. Hang a HV scope probe on some so 
called well designed amps and take a look. And then understand why those 
brands are notorious for premature filter failures.

I suggest a pair of .0047's or a .01 as the choke bypass, Then a 
vitreous enamel WW glitch resistor and another .01 to be sure of a clean 
HV. The resistor uses nichrome wire which has its own L and acts as a 
secondary choke to any funny stuff that gets by L-1.

Mouser carries Vishay 6KV discs as well as the resistors at very 
reasonable prices.

Carl
KM1H


----- Original Message ----- 
From: "Eddy Swynar" <gswynar at durham.net>
To: <amps at contesting.com>
Sent: Thursday, February 05, 2009 7:35 AM
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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