>>ALWAYS SHORT OUT UNUSED TURNS OF A
>>TANK COIL, whether a roller or switched circuit.
>? Amen. And the short should contain minimal R.
I've had problems with a transmatch by doing that. When most of the inductor
is in use, and there's only a few shorted turns, the currents in them can
cause problems - even at 150 watts. Similarly, I've had problems with not
shorting, because of resonance of the unused portion of coil with stray C to
the operating frequency. If you short, then as Rich says, it should be a
minimal resistance short, but be prepared to unshort if using most of the
coil. PA's are much more forgiving than transmatches in this respect,
because the amount of coil is more or less fixed by the frequency of
operation, rather than by the variable load impedance that a transmatch
sees.
73
Peter G3RZP
> ----------
> From: Rich Measures[SMTP:measures@vc.net]
> Sent: 08 January 1999 09:43
> To: amps@contesting.com
> Subject: Re: [AMPS] E F Johnson Roller
>
>
> >
> >I had a caliper and Johnson model 226-1 handy. The ribbon coil is .125 x
> >.250 silver plated copper. This model has 5 turns wide spaced and the
> >remainder close spaced. Johnson made other models besides this one.
> >
> >I was asked at one time why an amp using a roller coil arced. If unused
> >turns are not shorted out a transformer is created. Depending on where
> >the coil is tapped the open end can develope a rather large voltage (rf)
> >and really play havoc inside an amp. ALWAYS SHORT OUT UNUSED TURNS OF A
> >TANK COIL, whether a roller or switched circuit.
> >
> ? Amen. And the short should contain minimal R.
>
>
> Rich...
>
> R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
>
>
> --
> FAQ on WWW: http://www.contesting.com/ampfaq.html
> Submissions: amps@contesting.com
> Administrative requests: amps-REQUEST@contesting.com
> Problems: owner-amps@contesting.com
> Search: http://www.contesting.com/km9p/search.htm
>
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|