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From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <AANLkTinHC6VEy9e4OofWJRGxsiDRhhUe7xP=D-Gfx8Pf@mail.gmail.com>	<004701cbb0d8$25d56e40$0401a8c0@xphd97xgq27nyf> <AANLkTi=DBN4EPGrsv=X7kKxrUvqnoemDMhMJPPm2r9q2@mail.gmail.com> <4D2B293F.80608@telia.com>
Date: Mon, 10 Jan 2011 16:56:01 -0000
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Subject: Re: LF: Re: Capacitor warning
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Hi Johan that looks like a "professional" version of the QST article. The
first referance I have is somewhere around 1977 from EDN I think ....I read
the original and copied it for future use....25 years later !!

Inductors, variable, tuning for the use of.......
I found that there are two sizes of white waste-pipe at the DIY (Focus is my
nearest) a coil of 18swg wire on the smaller diameter will just slide inside
a coil on the larger diameter pipe. You dont need many turns on the inner
"moving" coil and it should onlu need to get near to the larger coil or
maybe just overlap. Another useful way of making a variable L is to find a
couple of iron-dust toroids that will slide into the coil former with the
toroid axix allong the coil axis .....use plastic bolts, or threaded rod to
move this. Again arrange the coil to just be slightly smaller than required
then the core with barely penetrate the coil. I have tried this with an
"inductometer" but not tried it in anger with RF power.

All my (successful) Class-E experiments were conducted with RIFA PHE 428
series capacitors ( Blue  and from RS I think), WIMA do a similar series
(which I think are available from Farnell, and yellow in colour).

Note even older (Valve era) high voltage tubular foil caps have problems as
well because they are not rated to take the currents that will flow in Class
E output circuits ( my 150W breadboard showed 12A , confirmed by a Simetrix
simulation) The failure was a steady and permanent reduction in capacitance.
I think that the foil to lead-wire connection was fusing on individual
layers. I seem to remember the above RIFA PHE 428 caps were marked as "Pulse
Rated"

Go play and have fun....the FETs are cheap  enough.

Alan G3NYK
----- Original Message ----- 
From: "Johan H. Bodin" <jh.bodin@telia.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Monday, January 10, 2011 3:43 PM
Subject: Re: LF: Re: Capacitor warning and First 500kHz Class E breadboard


> Andy,
>
> the last two pages of
>
>
http://www.cs.berkeley.edu/~culler/AIIT/papers/radio/Sokal%20AACD5-poweramps.pdf
>
> is a nice and simple guide to the "two dimensional" tuning of the class E
> amplifier. The trick is to get Vdrain make a soft landing on the right
spot of
> the GND runway :-)
>
> By the way, adjusting L may be easier than adjusting C2, it has the same
effect.
>
> 73
> Johan SM6LKM
>
> ----
>
> Andy Talbot wrote 2011-01-10 16:18:
> > Well, the first breadboard with only vaguely correct values worked OK  -
so it
> > doesn't look too be all that critical.  Design Q of teh tank circuit is
5, so
> > values won't be that important.   No need to tap the L measure and get
it right
> > to start with,then use parallel C to fine tune the finished amp.    With
this
> > sort of Q. "narrow band" for class E probably means > 10kHz
>