[Amps] L4B biasing

[Jim W7RY]

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.

73
Jim W7RY


-----Original Message----- 
From: Paul Baldock
Sent: Wednesday, December 24, 2014 1:23 PM
To: mikflathead at aol.com ; amps at contesting.com
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.
>_______________________________________________
>Amps mailing list
>Amps at contesting.com
>http://lists.contesting.com/mailman/listinfo/amps


---
This email has been checked for viruses by Avast antivirus software.
http://www.avast.com

_______________________________________________
Amps mailing list
Amps at contesting.com
http://lists.contesting.com/mailman/listinfo/amps