[Amps] 813 efficiency

[Jim Thomson]

Date: Sat, 23 Feb 2013 07:22:45 -0500
From: Eddy Swynar <deswynar at xplornet.ca>
To: Jim Thomson <jim.thom at telus.net>
Cc: amps at 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