Date: Sat, 23 Feb 2013 07:22:45 -0500
From: Eddy Swynar <deswynar@xplornet.ca>
To: Jim Thomson <jim.thom@telus.net>
Cc: amps@contesting.com
Subject: Re: [Amps] 813 efficiency
On 2013-02-22, at 11:14 AM, Jim Thomson wrote:
>
>
> ## eddy, toss the books. Spend 5 mins with the GM3SEK PI software instead.
> The L PI is the ticket, but it can take many variations. With higher amounts
> of L in the plate lead ( anywhere b4 the tune cap)
> you require less L in the main 10m coil..and vice versa. You can see that
> effect right away in the software. There is NO reason to have to switch that
> coil out of the circuit, why bother ?
Because the tuning on the lower bands was radically altered with it in, far &
away removed from quoted "text book specs" for a pair of 813s in GG...
~73~ de Eddy VE3CUI – VE3XZ
### How can a tiny coil in the plate lead possibly screw up the tuning on the
lower bands ? The most it will do is lower the plate load Z on10m a whole
bunch... and lower it a little bit on 15m,
and even less on 20m. A tiny bit on 40m..and next to nothing on 80m. I had a
hb 2 x 813 GG amp back in 1974..and it too had the L–PI config. 80-10m.
## The L-Pi was also used in other folks 813 amps, same deal. The
3CX-3000A7 amp also uses the L-Pi, and that tube is 33 pf of c from anode to
chassis, when plugged into the socket.
The tube itself is 24 pf, and the other 9 pf is between the anode to chassis,
caused by the proximity of the anode to the chassis. The L-PI was also used
on the 3x6..which is 40 pf.
## The YC-156 is one of the worse for C.... 35 pf..which rises to 50 pf, when
bolted to the chassis. The L-PI is used there too. Baffles me why you would
have to shunt out the tiny coil when on the
lower bands.
Jim VE7RF
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