My experience has been the full opposite but not with the 275 w.
model. I own two KW Matchboxes and use them with center fed 80 and
20 m. halfwave dipoles. I bought one on-line and the other at a
hamfest. My experience was that I only needed to take off the cover,
hose the chassis and components down in my shower, let it air-dry and
do some cleanup with deoxit, and I had a balanced matching network
rated at about 2500 watts. That's 1 KW input AM at 100% modulation.
The KW matchbox was made to be used with the Johnson Desk KW.
Getting back to my earlier point about higher power handling
capability being the better choice even if you do not need to operate
QRO, I would avoid the 275 w. Matchbox and try to get a KW model. I
find mine are useable on the WARC bands also. The one band they do
not cover is 160.
The modern day antenna tuners are of inferior construction compared to
the build quality and parts used in earlier tuners such as the BC-939,
180S-1 and KW Matchbox. But recent vintage tuners usually work okay
for modern day hams because they typically operate with low duty cycle
modes. Why are modern tuners not of such high quality? Because
today's manufacturers do not have the in-house plant tooling needed to
economically make components such as plated edge-wound roller
inductors, Cardwell Johnson or National quality capacitors with
ceramic parts and brass gear turns counters. If you look inside a KW
Matchbox you will see silver contact switches, a large open frame TR
relay (if it has not been removed), high voltage air variables that
only Johnson could make for themselves, edge wound air inductors and
porcelain shaft decouplers -- things you'll never see in a modern
tuner, and if you did, it would probably not be affordable for most
hams.
The Ten Tec 238 is okay for unbalanced feeds and everything except
maybe a long continuous duty transmission on 160, but if you open one
up and put it next to a 180S-1 there is no contest. But, it is also
an unfair comparison for the modern day Ten Tec company must make and
sell a product within the limits set by today's economy and hams's
budgets and make a profit. With that they do quite well.
I would not evaluate a tuner only on its ability fo find a match over
a wide range. Some of those T networks do that and can be very
inefficient under certain circumstances. Today's hams seem to want a
single do-everything match-anything box. Let's say you have one that
can let you use a 30 foot pipe on 160 m. (that's a heck of a lot of
current in that tuner.) Wonderful, except do you really want such a
poor antenna for 160? It is one thing to use a tuner to cover
several bands with an efficient antenna but if the tuner can't find a
match, maybe it is telling you that you need a better antenna; not a
box that makes a bad antenna, (often one too small and/or too low with
a very low Z) look good to the transmitter.
73
Rob
K5UJ
<<<The big problem now days Jerry is that most of them you find at the flea
market look "fair" on the outside, but if you open them, you close them real
quick and walk away.
I've seen lots of melted coils in the 275w version, and most everything
inside is generally so corroded, it looks like you would have to sand-blast
it to get it to the state you would want.
Time has taken its toll on most of these units.
I highly recommend never to buy one of these sight unseen.
If you can find a clean one and only need a couple of bands, they are
excellent boxes.
If you expect them to match any and everything across all of our HF bands,
you will be very disappointed.
They simply do not live up to their reputation. Not at all.>>>
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