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Re: [Amps] power limiting in 8410 amps?

Subject: Re: [Amps] power limiting in 8410 amps?
From: Jim <>
Date: Sun, 4 Nov 2018 20:49:18 -0600
List-post: <>
The Drake L4B only need 2-4 diodes for bias. The less ZSAC the harder it is to drive.


Jim W7RY

On 11/3/2018 12:25 PM, Jim Thomson wrote:
Message: 2
Date: Fri, 2 Nov 2018 18:35:30 +0000 (UTC)
From: Russ Williams <>
To:, Steve Bookout <>
Subject: Re: [Amps] power limiting in 8410 amps?

< Steve.? I would thrilled to get 1200 watts out of my L4B with 40 watts drive .

<Russ KW6T

##   40 watts to drive an L4B to  1200 watts.... not gonna happen anytime soon, 
not with
2500 vdc under load..and  800 ma plate current.   I get 1290w pep out of my  4 
x L4Bs
on 80m, with calibrated watt meters..and abt  100w pep  drive.

## The best you can do with the L4B, is to toss the grid chokes and grid 
caps..and directly bond
the 3 x grid pins to the chassis.   Then install  10 x 1N5408 diodes  in 
series...for bias.   Drakes  scheme
of   operating the pair of  3-500Zs  with no bias..and  220-230 ma of idle 
current is  fubar..ditto with
the pair of  50 watt, 50 k bleeders  in the outboard  L4PS   B+  supply..not 
required.   Drakes scheme
of using +  130 vdc  for cut off bias on RX is more fubar.... a  50 k ohm  @  3 
watt  mof is ample for that
job,  just rewire  the  center pole of the  3PDT  TR relay to shunt out the  50 
K on TX.

Then the L4PS runs stone cold.   With grids bonded directly to chassis, the amp 
is easier to drive, typ
20-25 watts  LESS drive required..... but some of that gets negated by adding 
the 7 vdc of bias.

Jim   VE7RF

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