Date: Tue, 6 Oct 2020 06:11:38 -0500
From: Rob Atkinson <ranchorobbo@gmail.com>
To: "amps@contesting.com" <amps@contesting.com>
Subject: Re: [Amps] SB220 running plate current when no drive; Problem
found
<3-500s may still be in production but the cost is high compared to
<years ago and quality may be questionable.
<Good tubes in ham service should last for decades. There are SB220s
<out there with the original Emacs going strong.
<A tube failure is due to one or more of the following: Poorly made
<tube, improper operation, or poor amplifier design.
<Ameritron has a single 3-500 amplifier they advertise as a 1 KW output
<amp. Anyone who drives that single tube to that level all the time
<will have to get a new 3-500 every few years.
<Rob
<K5UJ
## The ameritron AL-80B...running at 1000 pep output with a single 3-500Z
is pure fantasy....esp when it only has aprx 2700-2750 volts loaded at
550 ma.
## apparently, the 550 ma rating is..the ICAS tube rating. Thats a new
one for me.
No mention of any icas ratings on any tubes in the eimac catalog....unless
its for pulse service,
with extremely low duty cycle, and typ 10 microsecond long pulses.
Apparently Eimac approved
of the icas ssb rating, for ssb use. On CW mode, the AL-80B is rated for
850w out....running 500 ma.
## W8JI tested every brand of 3-500Z...and only one of em would do 1000 w
pep out with -35 db IMD.
## chinese 3-500Z’s, when run at 1 kw pep out for a single 3-500Z, typ
last 5-6 years max. Same chinese
tubes in a SB-220, L4B etc, will last longer.
## eimac catalog depicts 400 ma for a 3-500Z. A better way to run the
3-500Z, would be to use more B+.
Back in the 70s I had a hb single 3-500Z..and used well over 4 kv no load.
Then plate current could be reduced
a bunch..to get 600-700 watts out.
## I know several folks who are still using the original eimac 3-500Zs in
their 80s built SB-220s.
## another option is to stuff a 4-400A / B /C into the socket. But they
have to be run with zero bias.
Also the grid pins have to be directly bonded to chassis. Grid caps and grid
chokes have to be removed.
Jim VE7RF
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|