----- Original Message -----
From: "Mike" <noddy1211@sbcglobal.net>
To: "'rbethman'" <rbethman@comcast.net>; <amps@contesting.com>
Cc: "'R Johnson'" <rjohnson@tmlp.com>
Sent: Saturday, November 05, 2011 8:24 PM
Subject: Re: [Amps] Gettering 3-500 Tubes
This is good advice from Bob, if you must use the old tubes that you don't
really know if they are worn out anyway, I would just get a pair of new
ones if it were me, I am talking from experience.
The only reason I went through the gettering process was that I had a New
never used SB-221 and brand new Eimac 30 year old tubes and thought it would
be nice to use those old tubes. The getting went fine, one tube was blue
for a while so I thought all was good. I put those tubes in my Six meter
mono band SB-220 and one tube flashed over at 1kw out, took out the
rectifier board and various capacitor with a pretty big bang, that took a
few minutes off my life: -)
So unless you are attached to those tubes for sentimental reasons I would
dump them or follow the instructions by PA0FRI at the least.
Also as mentioned the components used back then were not so good, so do
update the amp with Harbach boards etc.
http://www.harbachelectronics.com/main/page_products_sb220__sb221.html
If you want to keep the and use it, do the recommended modification and
updates. Not sure you need the "Parasitic Suppressor Kit", never really
proven to work in my mind, also the "Soft Start" probably not need for this
amp, but the "Soft Key board" needs to be done if you are driving it with a
solid state rig and also the "Rectifier/Metering Board" from Harbach would
be a really good move.
-Mike, K6BR
I dont particularly care for the Harbach PS board for the SB-220 family, Ive
had too many arrive here in customer amps that have the bias and HV metering
components blown out. Those parts are seriously undersized.
It just as easy to rebuild the original board with 1N5408's, Ohmite HV
resistors, and a string of 1N5408s's on perfboard for the bias. The filter
caps can be replaced with 330uF/450 Snap In type that fit the original
blocks perfectly. and 75K 3W MOX equalizers.
Soft Key is a good way to preserve the On/Off switch, especially when going
with higher value filter caps; otherwise it does nothing useful.
The parasitic stuff is pure voodoo. Ive covered the 21st century version on
here several times.
Carl
KM1H
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