In a message dated 1/20/2007 8:23:27 P.M. Eastern Standard Time,
ve5ra@sasktel.net writes:
the fact you have to be careful running a 3-500Z on 50MHz.
What we get away at on HF just doesn't fly up there unless
you have a lot of dumb luck, and it basically will ruin the
amp for any other use.
I DO NOT condone the addition of 6 meters to an Sb-220 by simply playing
with the 10 meter input coil and re-tapping the HF coil at some parasitic
area.
It simply is a bad idea and does "border on stability" in this aspect.
However, an 3-500 tube is rated to 110mhz by Eimac (that's a fact) and there
should be NO reason why a stable MONO band 6 meter amp can't be designed
around
them. I've been there and done that and EXPERIENCE tells me simply that it
is a bad idea. In this regard if it does work "OK" I'd say it is the stroke
of luck that some talk about here. On the other hand, in the mono band case
using the proper value components, proper layout, and a little voodoo magic,
one CAN make a nice stable 6 meter amplifier. After all, at 50mhz we are
only 1/2 way to the max rating on the tubes. I don't think the folks at Eimac
are a bunch of nut jobs.
I am not sure about this, but I would venture to say that probably only one
person has converted more Sb-200's and Sb-220's to mono band 6 meter
amplifiers than I. If that person were still with us on this reflector, he
could
probably attest to the fact that at this point in time about 7 out of 10 Sb-220
amps have at least one toasted contact on the bandswitch. They still work
because the contacts are redundant, but on close inspection, either the 15 or
10
meter contact are toast. Sure, the Sb-220 is an OK HF amp, but there are
much better ones! To take an Sb-220 that has a bad bandswitch and make it a
nice mono band 6 meter KW is really not a bad thing considering the
alternative in commercially available 6 meter tube amps.
I am wondering when the next sunspot cycle peaks and 6 meters is alive, will
more commercially made 6 meter amps pop up? Lou
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