Return-Path: Received: from mtain-dj10.r1000.mx.aol.com (mtain-dj10.r1000.mail.aol.com [172.19.187.146]) by air-mb04.mail.aol.com (v129.4) with ESMTP id MAILINMB042-a26e4d2b237677; Mon, 10 Jan 2011 10:19:18 -0500 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-dj10.r1000.mx.aol.com (Internet Inbound) with ESMTP id 323FA38000116; Mon, 10 Jan 2011 10:19:15 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1PcJVs-0003Dk-Qc for rs_out_1@blacksheep.org; Mon, 10 Jan 2011 15:18:28 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1PcJVs-0003Db-1d for rsgb_lf_group@blacksheep.org; Mon, 10 Jan 2011 15:18:28 +0000 Received: from mail-iy0-f171.google.com ([209.85.210.171]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1PcJVp-0000bg-9i for rsgb_lf_group@blacksheep.org; Mon, 10 Jan 2011 15:18:28 +0000 Received: by iyj21 with SMTP id 21so18389613iyj.16 for ; Mon, 10 Jan 2011 07:18:19 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:received:in-reply-to :references:date:message-id:subject:from:to:content-type; bh=PWyV5dGMXOQgZx6xi7Qq6KT3BJZznmuZ19MG1r4BBbI=; b=Mq8IFtRZWlyLg/ZUmGjFq3u6jegR/7EoPbc+0fJM79MQK8XDFCQERj6+mbMTQkHzVg XDlBZ+gNsAk8OU7FuMDRT+fLSqXX59R7vgX90PDi0uXU9l97gxlmkWHcjpOsRv9apnhD WTcu+wL1v8DjxtAsM2Oz2H6v/0ZK+8TBy6kiY= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=m/NOf1bqVom7g7PYCPGQW2nXUImtth5DY12tJyZ8SbBHbAOLgJpbcwyJ7uBrUbpuk6 bMfQYrAlc8NTtiLXb8JgQrYE2UKcnKGVhKm9QbknGlRjIZy+k38D3EXJqwB2yLx6N/Qb swnhO7G6Z/OpYcImYynTxPsg0PjFY2JSYNnGU= MIME-Version: 1.0 Received: by 10.231.13.137 with SMTP id c9mr28725361iba.37.1294672699046; Mon, 10 Jan 2011 07:18:19 -0800 (PST) Received: by 10.231.200.211 with HTTP; Mon, 10 Jan 2011 07:18:18 -0800 (PST) In-Reply-To: <004701cbb0d8$25d56e40$0401a8c0@xphd97xgq27nyf> References: <004701cbb0d8$25d56e40$0401a8c0@xphd97xgq27nyf> Date: Mon, 10 Jan 2011 15:18:18 +0000 Message-ID: From: Andy Talbot To: rsgb_lf_group@blacksheep.org DomainKey-Status: good (testing) X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: Re: LF: Re: Capacitor warning and First 500kHz Class E breadboard Content-Type: multipart/alternative; boundary=0022150467ef53bafb04997f7aa2 X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=HTML_MESSAGE autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false x-aol-global-disposition: G X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-m015.2 ; domain : gmail.com DKIM : pass x-aol-sid: 3039cdbc9d0f4d2b23731321 X-AOL-IP: 195.171.43.25 X-Mailer: Unknown (No Version) --0022150467ef53bafb04997f7aa2 Content-Type: text/plain; charset=ISO-8859-1 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 Yes - most certainly agree with "don't use ceramic caps" I resurrected a 10n one from the waste bin, connected the C meter (10.9nF at Room Temp) and turned a hair dryer on it. C reduced to 5.4nF as I was watching, and that was probably only around 50C. Blowing on it shifted the value noticeably. Andy www.g4jnt.com On 10 January 2011 15:07, mal hamilton wrote: > I designed and built a class E PA for 500 Khz when the band became > available. > I used some hefty poly caps in the PA and never used ceramic caps. > Use available caps to the nearest value and to fine tune pa, on the > frequency of interest, observing on a scope the waveform, tap the coil up > or down a couple of turns until the correct waveform is visible. > This amplifier is very robust and has given excellent service ever since. > My design is for 50 ohms and the TX is followed by a LPF then 100 yards of > coax to the base of my inv L antenna. Antenna is also adjusted for 50 ohms > match. > A class D amp is probably easier to build and needs no adjustments, other > than matching to the antenna. > ie Class D is a broad band device whereas class E is specific to the design > frequency. > g3kev > 6 > > ----- Original Message ----- > *From:* Andy Talbot > *To:* rsgb_lf_group@blacksheep.org > *Sent:* Monday, January 10, 2011 2:22 PM > *Subject:* LF: Capacitor warning and First 500kHz Class E breadboard > > A warning to anyone contemplating making power amps - especially class E > types. > Don't even think about using the small high voltage ceramic caps availalble > at low cost from the suppliers - and sold as "suitable for SMPSUs etc" in > resonant circuits > They are appalling, terrible, revolting things. You only have to breath on > them and they change their value.wildly > > These things http://www.g4jnt.com/Download/UselessCaps.jpg > > I've just made up a first version of a breadboard for a 500kHz Class E > amplifier, (target design 500W from 50 V supply), calculated the L/C values > as per Alan's spreadsheet, combined with an L matched output for 50 ohm. > For the capacitors I aimed to get within 5% of the calculated values using > many of these small ceramic objects in parallel - lots in || should share > the current, shouldn't they, which would be good? > > So I soldered them up - used the G4HUP L/C meter to measure the values - at > which point I should have been a bit suspicious as the measured C was > sometimes a fair bit lower than it should have been. At the time I just put > it down to "finger trouble" - one does tend to ignore little things like > that sometimes. > Anyway, made up the amp, used a 12V supply rail and monitored the switching > waveforms, expecting to see something vaguely approaching the half sine on > drains etc. > > Results, terrible, nowhere near what they should have been - clearly summat > was very wrong I remeasured the || combination of the caps - after > unsoldering they were sometimes as much as half the value they should have > been - until they cooled right down and approached room temp. Occasionally > a cap value approaching correct would show up on the meter once in a > while - but that was was probably just coincidence :-) > And yes, I did double, triple and quadruple check the meter against good > caps - it was OK every time. > > These little blue things appear to have a huge temperature coefficent - are > completely useless, designed to do nothing of value, and all have now gone > into the waste bin. > In fact, I was wondering if they were random-capacitors. > > I did have a just two trusted 22nF caps in the junk box that were within 20 > - 30% of the right values for the amp and an awful lot of 3.3nF 1700V things > of a more respectable heritage, so just put these into the circuit, tested > at 12V and got waveforms almost correct. Increased drive freq to 515kHz > (no real scope for changing cap values at this stage, so freq change would > be easier to try with) where the waveform looked best, and increased supply > volts. Got to 30V and it was delivering 150 Watts; 40V and was getting > around 350 Watts at which point I assumed it was going to work, so switched > off for a break. Wasn't going to tempt fate by gong to the full 50V having > not even bothered to tune things up properly > A picture of that breadboard can be seen at > http://www.g4jnt.com/Download/ClassE_BrdBd01.jpg > > The yellow cap shunting the device was running quite warm - which is hardly > surprising just a single poly[whatever] carrying all those amps - and the > one in series with the tank was slightly warm. So, now need to browse the > Farnell catalogue (the cubic printed paper version is easier) for some caps > that will do the job properly - like more of those yellow ones. Actually, > may have enough of the 3.3nF ones, but that would end up with lots in > parallel > > So, for anyone who is contemplating a class E amplifier design: > > Get close to the calculated component values and it will probably > mostly-work immediately. > Play with the drive frequency while monitoring waveforms to see which way > tuning needs to go > Don't use cheap high voltage ceramic capacitors > Don't use cheap high voltage ceramic capacitors > > They would work well in a random number generator tho..... > > Andy > www.g4jnt.com > > > > > --0022150467ef53bafb04997f7aa2 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable
Well, the=A0first breadboard with only vaguely correct values worked= OK=A0 - so it doesn't look too be all that critical.=A0 Design Q of= teh tank circuit is 5, so values won't be that important.=A0=A0 No ne= ed to tap the L=A0measure and get it right to start with,then use parallel= C to fine tune the finished amp.=A0=A0=A0 With this sort of Q. "narr= ow band" for class E probably means > 10kHz
=A0
Yes - most certainly agree with=A0 "don't use ceramic caps&q= uot;
=A0
I resurrected a 10n one from the waste bin, connected the C meter (10= .9nF at Room Temp)=A0 and turned a hair dryer on it.=A0=A0 C reduced to 5.= 4nF as I was watching, and that was probably only around 50C.=A0=A0
Blowing on it shifted the value noticeably.
=A0
Andy


=A0
On 10 January 2011 15:07, mal hamilton <g3kevmal@talktalk.n= et> wrote:
I designed and built a class E PA for= 500 Khz when the band became available.
I used some hefty poly caps in the PA= and never used ceramic caps.
Use available caps to the nearest val= ue and to fine tune pa, on the frequency of interest, =A0observing on a sc= ope the waveform, =A0tap the coil up or down a couple of turns until the= correct waveform is visible.
This amplifier is very robust and =A0= has given excellent service ever since.=A0
My design is for 50 ohms and the TX= is followed by a LPF then 100 yards of coax to the base of my inv L anten= na. Antenna is also adjusted for 50 ohms match.
A class D amp is probably easier to= build and=A0needs no adjustments, other than matching to the antenna.
ie Class=A0D is a broad band device= whereas class E is specific to the design frequency.
g3kev
=A0=A06
----- Original Message -----
Sent: Monday, January 10, 2011 2:22= PM
Subject: LF: Capacitor warning and= First 500kHz Class E breadboard

A warning to anyone contemplating making power amps - especially clas= s E types.
Don't even think about using the small high voltage ceramic caps= availalble at low cost from the suppliers - and sold as "suitable fo= r SMPSUs etc"=A0=A0in resonant circuits
They are appalling, terrible, revolting things.=A0 You only have to= breath on them and they change their value.wildly
=A0
=A0
I've just =A0made up a first version of a breadboard for a 500kHz= Class E amplifier, (target design=A0500W from 50 V supply),=A0 calculated= the L/C values as per Alan's spreadsheet,=A0combined with an L matche= d output for 50 ohm.=A0 For the capacitors I aimed to get within 5% of the= calculated values using many of these small ceramic objects=A0in parallel= - lots in || should share the current, shouldn't they, which would be= good?=A0=A0
=A0
So I soldered them up - used the G4HUP L/C meter to measure the value= s -=A0at which point I=A0should have been a bit suspicious as the measured= C was sometimes a fair bit lower than it should have been.=A0 At the time= I just put it down to "finger trouble" - one does tend to ignor= e little things like that sometimes.=A0=A0=A0
Anyway, made up the amp, used a 12V supply rail and monitored the swi= tching waveforms, expecting to see something vaguely approaching the half= sine on drains etc.
=A0
Results, terrible, nowhere near what they should have been - clearly= summat was very wrong=A0 I remeasured the || combination of the caps - af= ter unsoldering=A0they were sometimes as much as half the value they shoul= d have been=A0 - until they cooled right down and approached room temp. Oc= casionally a cap value approaching correct would show up on the meter once= in a while=A0-=A0but that was=A0was probably just coincidence :-)=A0
And yes, I did double, triple and quadruple check the meter against= good caps - it was OK every time.
=A0
These little blue things appear to have a huge temperature coefficent= - are completely useless, designed to do nothing of value, and all have= now gone into the waste bin.
In fact, I was wondering if they were random-capacitors.=A0=A0
=A0
I did have a=A0just two=A0trusted 22nF caps in the junk box that were= within 20 - 30% of the right values for the amp and an awful lot of 3.3nF= 1700V things of a more respectable heritage, so just put these into the= circuit, tested at 12V and got waveforms almost correct.=A0=A0 Increased= drive freq to 515kHz (no real scope for changing cap values at this stage= , so freq change would be easier to try with) where the waveform looked be= st, and=A0increased supply volts.=A0=A0=A0=A0=A0 Got to 30V and it was del= ivering 150 Watts; 40V and was getting around 350 Watts at which point=A0I= =A0assumed it was going to work,=A0so switched off for a break.=A0=A0=A0Wa= sn't going to tempt fate by gong to the full 50V having not even bothe= red to tune things up properly
A picture of that breadboard can be seen at=A0=A0 http://www.g4j= nt.com/Download/ClassE_BrdBd01.jpg=A0
=A0
The yellow cap shunting the device was running=A0quite warm - which= is hardly surprising just a single poly[whatever] carrying all those amps= - and the one in series with the tank was slightly warm.=A0=A0=A0 So, now= need to browse the Farnell catalogue (the cubic printed paper=A0version= is easier) for some caps that will do the job properly - like more of tho= se yellow ones.=A0 Actually, may have enough of the 3.3nF ones, but that= would end up with lots in parallel
=A0
So, for anyone who is contemplating a class E amplifier design:
=A0
Get close to the calculated component values and it will probably mos= tly-work immediately.
Play with the drive frequency while monitoring waveforms =A0to see wh= ich way tuning needs to go
Don't use cheap high voltage ceramic capacitors
Don't use cheap high voltage ceramic capacitors
=A0
They would work well in a random number generator tho.....
=A0
Andy
=A0
=A0
=A0

--0022150467ef53bafb04997f7aa2--