Rich says:
>Sure, Delrin can typically be used for spreaders on 300 ohm ladder-line
>in open air, except perhaps in July and August, with a SB-200, but the
>high potentials typically encountered in an antenna tuner's roller
>inductor(s) with 1500w of RF can cause Delrin to melt and combust. .
I wouldn't even recommend it for spreaders, unless you're looking to
replace them every few years because of the ultra violet degradation.
But how about an application as an RF firelighter?
Tom commented:-
>> It is leakage reactance, as opposed to winding resistance that
limits
>> the current? If so, what's the power factor, or doesn't one worry?
>Hi Peter,
>It is the transformer's ESR, not leakage reactance, that limits
>inrush current.
>The ESR, as you seem to know, is mainly a combination of primary
>and secondary copper losses, core losses, and flux leakage....in that
>order. Flux leakage is by far the most insignificant of the three,
>generally being so small it is ignored in the transformer's design
>process.
and Rich said:
>>It is leakage reactance, as opposed to winding resistance that limits
>>the current? If so, what's the power factor, or doesn't one worry?
>The current limiting is done with the core.
which comments have confused me. Rich seems to be suggesting that
limiting is derived from core saturation - or am I misunderstanding?
Tom, I think that you're suggesting that the current limiting mechanism
in the SB220 is the 'usual' one in a transformer. I was wondering if the
transformer in the SB220 had been specially designed to have a high
leakage reactance so that the inrush current was limited - that was done
on a Marconi high power tx back in the '60s, ( I think it was pure
serendipity, as there was 30Kv insulation between primary and secondary
for other reasons) but it sounds as if leakage reactance is not the case
for the SB220.
Joe, W8IK, is re-iterating the point I made some time ago - what we can
do in a home brew isn't always practicable in manufacture. A good rule
of thumb is that you sell for twice what it costs to make, and it's a
fair bet that labour (English spelling!) is half the cost of
manufacture. So if it costs $20 in parts, that is likely to come out at
$80 in selling price - you might shave it down a bit if things are
really competitive, but I suspect that labour costs are reasonably high
- I doubt very much if Ameritron, QRO or Alpha are paying minimum wage,
as assembling amplifiers is hardly a job for totally unskilled labour.
And when you consider the technical depth of discussion on this
reflector as a guide to the skills needed, you can bet that the design
engineers aren't on minimum wage either. How much is it worth to
possibly extend the life of the 3-500 from say 1000 to 2000 hours?
Amortize out the cost of the tube over the number of hours - cents per
hour - as opposed to getting 5% or whatever on the same amount of cash
over the number of years that people do have the tubes lasting for.
I have seen commercial amps with filament rheostats - even one with a
magnetic amplifier -never an amateur one for the reason above.
Finally, Gary, NI6T says:
>From the UK, I like the imported Sam Smith's Yorkshire Pale, when
>available and affordable, or good old Bass.
Those who went to the upstairs bar in the Crowne Plaza (Stouffers as
was) will possibly have noted that they had Sam Smiths this year. I
warned them to get more when I arrived on the Wednesday - they did - and
still ran out on Saturday! Hopefully, they'll do better next year.
73
Peter G3RZP
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