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Re: [Amps] Plate coupling capacitor value

To: "Bill Turner" <>, "Amps group" <>
Subject: Re: [Amps] Plate coupling capacitor value
From: "Carl" <>
Date: Sat, 9 Sep 2017 20:30:56 -0400
List-post: <>
That goes back to the late 30's when SW broadcasting went above the 25, 22, and 19M bands and were still using older design tubes.

The actual circuit was to tap the coil that was computed at a convenient point at dead center or less. A center tap resulted in a 4X increase in the Tune C while taps at lesser turns had less of an effect.

For a ham amp the tap to allow full 10M tuning also affects lower bands and is a wash by 20M. My first use of this was in the 70's to enable 4 GG 813's to cover 160-10 which they did quite well at 3000V.

A pair of 803's were also used at about 1200W out 80-20 also at 3000V the same way.

More recently a Clipperton L was converted to 6M.where they were happy at 1200-1300W.


----- Original Message ----- From: "Bill Turner" <>
To: "Amps group" <>
Sent: Saturday, September 09, 2017 1:08 PM
Subject: Re: [Amps] Plate coupling capacitor value

------------ ORIGINAL MESSAGE ------------(may be snipped)

On Sat, 09 Sep 2017 16:53:24 +0000, Manfred wrote:

Specially if tubes are used that have a lot of internal and stray
capacitance, the loaded Q of the PI tank typically has to be rather high
on 10 meters


There is a better way to tune 10 and 12 meters despite high tube
output and stray capacitance. A small coil in the anode lead will
create an "L" network which reduces the plate impedance on those bands
and permits use of a larger tune capacitor. This technique is
discussed in the amplifiers section of any recent ARRL handbook. I
have used it on all my HF and six meter amps and it works like magic.
Try it, you'll like it!

73, Bill W6WRT

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