Dipoles at even multiples of the main frequency have a problem. The two
bands you mention should be the most difficult to tune with the tuner -
regardless of the balun question. These two bands put the feedpoint at/near
a high impedance feed point on the antenna. On 20 you have two half waves,
one on each side and on 10 you have two full waves. If you do match it,
the balun has to be able to handle the voltage. 10 being so wide, some part
of the band may be a better Z for the tuner to handle.
My guess is that the tuner (not) matching these bands will be a bigger
problem than balun survivability. It has to handle an impedance "at the
outer edge" of the Smith chart, so to speak. It may do it for certain
feedline lengths, but not others. I don't know enough about the capability
of these tuners to be more specific 0 except that the few I have seen specs
on specify the Z range over which they can match, so if the Z at the tuner
is outside that range...tilt.

The 40M 1/2 wave dipole (or inverted V) will work fine on 30, 17 & 15 and
probably 12 & 60 where the tuner shouldn't have to strain too much, so to
speak. I've used my 40 M Inverted-V with my MFJ tuner on all these but 60
(and of course 20 & 10). I even managed to load it on 75 with my MFJ tuner
& work the east coast, but that's not a good thing. Just wanted to try.

--
Steve N, K,9;d, c. i My email has no u's.


"Frank MacKenzie-Lamb" wrote in message
...
Hi folks,

I've moved to a country area in central MA and will be putting up a 40m
diople. Considering using a balun with my AT-250 tuner with mt TS-430.
If the tuner can tune in 20 and 10M, will damage be done to the 1:1 balun?
Thanks
NG1I