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Re: [Amps] L4B biasing

To: <>
Subject: Re: [Amps] L4B biasing
From: "Jim W7RY" <>
Reply-to: Jim W7RY <>
Date: Wed, 24 Dec 2014 22:14:01 -0800
List-post: <">>
11 diodes (7 volts) is way too much bias voltage.

Better to have about 3 diodes (1N5408). That is what I have found while designing my QSK circuit board for the Drake. The L4 and L4B was designed with Amperex 8802 tubes. They did not require bias because the idled at a much lower current than Eimac 3-500 tubes. And the old L4 was designed around the 3-400 (8163) which did not require bias either.

Sure, if you have 3800 volts of plate voltage then 7 volts of bias is fine. The SB220 used a 5.1 volt zenner and the SB220 plate voltage was around 3200 volts.

Jim W7RY

-----Original Message----- From: Paul Baldock
Sent: Wednesday, December 24, 2014 1:23 PM
To: ;
Subject: Re: [Amps] L4B biasing

Yes you should add bias. I added 11 diodes in the center tap of the
filament trany. So that would be about 7 volts.

- Paul

.At 12:52 PM 12/24/2014, you wrote:
I just finished me Drake power supply. I used a Drake transformer and a doubler board with 8 caps. I have 2600 volts showing on the high voltage meter. I have eliminated all the bias circuit in the power supply that Drake used. At idle I show 200 mills of plate current. My question is should I add a bias circuit? I purchased a W4ZT board but wonder if I need it. Thanks and Happy Holidays to all.
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