Dan Richardson wrote in message . ..
On Fri, 10 Oct 2003 11:07:53 -0700, Jack Twilley
wrote:

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

I recently sat down and calibrated my antenna, going through the bands
and recording the antenna tuner settings required to reach 1:1 on all
the bands my rig can run.

I'm thinking about another calibration I'd like to perform with the
tuner bypassed, trying to determine where on the bands I can use the
antenna without a tuner and still be within a reasonable SWR range.

I am hoping to preserve the lifetime of my tubes and maximize the
power available to me.

My question is: what is an acceptable SWR range? I know that 1:1 is a
desirable SWR, but when does SWR become undesirable to the point that
it shortens the lives of my tubes?

I am using a Kenwood TS-520 and an MFJ Versa Tuner II.

Jack.

Jack,

The 520 has a pi-network output. When properly adjusted, the pin-net
work will match the finals to the load. So if you are able to adjust
your plate and loading controls to the recommended grid and plate
current values everything will be just fine reguardless of the SWR.
Now if your SWR is so high as the 520 will not load properly then you
should think of bringing the tuner on line. Otherwise just leave it in
the by-pass position. Nothing is gained using the tuner if it isn't
needed.

Yep, if the rig will tune up with the loading control within it's
range, there is no need for a tuner. The 520 has it's own limited
range tuner built in.:)
If the load is 50 ohms, "IE dummy load, or 1.1 SWR antenna. the
loading control should be about 1/3 range. If the load Z is lower, the
load control will end up on the lower end. If the load Z is higher
than 50 ohms, the load control will end up at a higher setting. No
matter, as long as it's within it's range when you achieve a full
power tune. As far as the tuner, I would be more concerned with using
the absolute minimum inductance to get a usable match, than I would be
to get a perfect 1 to 1 match. This would give you the least tuner
losses. Also, the 520 has a "tune" mode setting. Good for initial ALC
and drive peaking , etc. But he should always do the final tuneup in
CW mode. Otherwise, he will end up underloaded if he tunes using the
"tune" mode only. This could cause splatter on fone. The 520 is a very
good older rig. The original 520 came out in the early to mid 70's.
I've had an orignal 520, and also a 520s. The 520 I had was a basket
case I bought for $100 about 4-5?? years ago. I overhauled it, and it
was a real nice rig. Very smooth audio. I had the 520s in the late
70's when it was still fairly new. I sold the 520 I rebuilt for $225
to a friend who was getting back into radio after 20 years off. He's
since sold it, and who knows where it is now. I still have a TS-830s
and VFO-230. Probably the best radio I have as far as pure
performance.
It's hard to kill an old hybrid kenwood rig. Anyway, the answer to his
main question is any match that lets the rig tune up within it's
loading range is good enough. If not, switch the tuner inline. BTW,
it's hard to kill a 6146 unless you really abuse it. I rarely have
toasted a 6146. But I used to go through drake's 6JB6's once every
year or two when I ran drakes all day long and retuned about 8-10
times a day switching bands. :/
The plate dissipation of the 6146A is 25 watts. A 6146B, 35 watts.
The 6JB6 sweep tube a puny 17.5 watts. The original 520 came with
"A's". MK