This Thread is interesting,
I have not dig into this old beast of a SB-220 yet to remember how or
what the circuit is composed of. But back in the 80's This SB-220 had a
mod added that made it run a LOT cooler because even when the amp was
placed in transmit mode, unless there was watts going in, there was zero
idle current.
I honestly do not remember exactly how this was accomplished. tho.
Joe WB9SBD
Sig
The Original Rolling Ball Clock
Idle Tyme
Idle-Tyme.com
http://www.idle-tyme.com
On 12/13/2016 1:21 AM, gudguyham--- via Amps wrote:
Self cut off bias has NOTHING to do with operating bias! Operating bias is set
by Zener diodes or a string of diodes in the CT return of the filament
transformer. The more string diodes or the higher the Zener voltage the lower
the idle current. Zero bias means no operating bias added to the normal
current draw of the tubes. So, remove or short out any zener or string diodes
in the CT and allow the amp to idle at its normal zero bias value and watch
your output increase.
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-----Original Message-----
From: Michelle <michelle_melt@windstream.net>
To: amps <amps@contesting.com>
Sent: Tue, Dec 13, 2016 12:51 AM
Subject: [Amps] Drake L4B to 6 Meters Help
-----Original Message-----
From: Paul Baldock
Sent: Monday, December 12, 2016 10:51 PM
To: Michelle ; <a href="mailto:amps@contesting.com";>amps@contesting.com</a>
Subject: Re: [Amps] Drake L4B to 6 Meters Help
Michelle
Did you say that you are running the 2 tubes a zero bias and have
about 100mA idle current. I think it should be more like 200mA in the
SSB position. This would suggest that either your high voltage is
low, or that one tube is not working/connected. One tube would be a
good reason for only getting 600W PEP.
- Paul
Paul,
The 100 ma idle current was due to the "self" cut off bias mod I installed,
I have since found out 100 ma is to low and
I am in the process of trying to raise it back up.
Michelle
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