[AMPS] Amp for RTTY?

[Doug Hall]

Hi amp folks,
I'm currently searching for a 100% duty cycle amp for RTTY contesting
use. I'd also like it cover 160m and run legal limit. Obviously the
easy answer is to buy an Alpha or Henry or whatever the amp d'jour is.
But given that I can't (or won't) justify the cost of such an amp,
what are the most reasonable alternatives? I'm willing to relax the
specs a bit, ie. I could live with 1200w or so instead of 1500w as
long as it would hold up in a 48 hr RTTY contest. As far as 160m
coverage goes, I seldom use that band at present except for occasional
stints on AM with an old Johnson Ranger, but one of these days I'd
like to chase some DX on 160m. Here's what I'm considering:

1. Build an amp using a somewhat reasonably priced tube or pair of
tubes, ie 4CX1600B, 4-1000A, 3-500Z, etc. I have some limited
experience with amp and power supply building from a previous job
where we produced a commercial amp using an 8877. I've chased
parasitics and plate choke resonances and such, so I think I could
build such an amp and get it working. But I just finished pricing the
4CX1600B amp project shown in the latest ARRL Handbook, and the only
way I can justify such a project is if I can scrounge components at
upcoming hamfests and off the net. Otherwise I'd come out cheaper
buying an amp. Building quantity 1 of a legal limit amp is not cheap
if you buy all new components, and I don't have many amp parts laying
around here. I envy some of you your junkboxes.

2. Take a reasonably priced used amp (ie. SB-220, L-4B, etc) and add
160m, additional cooling, and a stiffer power supply.

3. Buy two SB-220's and run them into a combiner (or separate antennas
if I want) at 600-700 watts each. Don't laugh - two SB-220's, a
splitter and combiner can be had for a little over $1K, and this gives
me a backup amp in a contest if I lose one, albeit at reduced power.
This doesn't address the 160m requirement, however.

Anyway, those are some things I'm thinking about. I recently picked up
an SB-220, and it works very well, but I don't know how hard I could
push it during an RTTY contest. I got kinda longwinded on 20m the
other night while ragchewing on RTTY with AP2TJ, and while the plates
were glowing nicely nothing seemed excessively hot at 700-800 watts
out. SB-220 owners - how hard can you push this amp without bringing
on an early demise? And what's the limiting factor? Power supply,
cooling, or tank components? All of the above? And while we're on the
subject, how much power should you get out of an SB-220? My amp has
the original tubes in it, and I get around 1100 watts out on 20m,
although I'm embarassed to admit that my only wattmeter is the one
built into my MFJ tuner. (OK, so I need a real wattmeter, too.)

As I said, I know that the easy way is to buy a 100% duty cycle legal
limit amp. For those of you who have them, more power to you,
(literally and figuratively!) but I'm looking for the Next Best Thing.

Your comments are welcomed. I've been on this reflector for a little
over a month now and have really enjoyed it.
73,
Doug, KF4KL
===========

"People don't care how much you know until they know how much you
care."

--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm