The Drake L4B only need 2-4 diodes for bias. The less ZSAC the harder it
is to drive.
73
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 <hrd998cc@yahoo.com>
To: Amps@contesting.com, Steve Bookout <steve@nr4m.com>
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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