ORIGINAL MESSAGE:
At 03:22 AM 5/16/2006, Peter Chadwick wrote:
>Down at the 100 watt level, it's very practical, but up at 1500
>watts, it's a bit more complicated, and I'd suggest you need to do a
>number of calculations before jumping in. The biggest problem I see
>is the total unwieldyness of winding really thick wire on to the
>core. Incidentally, you'll be stuck with using dust iron, and you
>need polytetrafluorethylene (trade mark name is Teflon) insulation
>on the wire, or in suitably thick 'cheeks' on the toroid. At the end
>of the day, at 1500 watts, I think that the air wound coil is rather
>more practical, although I'm aware that amps have been done with toroids.
*********** REPLY SEPARATOR ***********
I second Peter's comments, with an additional observation. I have a
Command HF-2500 legal limit amp which uses a toroid in the 40/80/160
meter portion of the tank coil. It is a heavy item, wound with large
teflon wire and well insulated. In spite of this I have burned up two
of them in the last five years doing RTTY contesting, which is
probably the most demanding of all amateur operations.
I think the engineers at Command were surprised to see an apparently
over-engineered coil burn up not once, but twice. They told me they
are coming out with a "Magnum" version of the HF-2500 which will
address this issue.
Bottom line: If you go the toroid route, plan on a large safety
factor in your design and even then, do some extensive high power,
long term testing lest you be unpleasantly surprised someday.
Bill, W6WRT
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