[Amps] FW: Re: tank coil heating

[Bill Turner]

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.


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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