Return-Path: Received: from mtain-dh08.r1000.mx.aol.com (mtain-dh08.r1000.mx.aol.com [172.29.65.28]) by air-mc07.mail.aol.com (v129.4) with ESMTP id MAILINMC072-a97c4d2b211c295; Mon, 10 Jan 2011 10:09:16 -0500 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-dh08.r1000.mx.aol.com (Internet Inbound) with ESMTP id B205B3800010C; Mon, 10 Jan 2011 10:09:09 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1PcJLp-00031F-0P for rs_out_1@blacksheep.org; Mon, 10 Jan 2011 15:08:05 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1PcJLn-000316-Fu for rsgb_lf_group@blacksheep.org; Mon, 10 Jan 2011 15:08:03 +0000 Received: from out1.ip09ir2.opaltelecom.net ([62.24.128.245]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1PcJLl-0000Su-3H for rsgb_lf_group@blacksheep.org; Mon, 10 Jan 2011 15:08:03 +0000 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: Ai8FANuvKk1cHY2R/2dsb2JhbACSHwOSH3O7EoJ8glAEgV+MZYJc X-IronPort-AV: E=Sophos;i="4.60,301,1291593600"; d="scan'208,217";a="464272954" Received: from unknown (HELO xphd97xgq27nyf) ([92.29.141.145]) by out1.ip09ir2.opaltelecom.net with SMTP; 10 Jan 2011 15:07:53 +0000 Message-ID: <004701cbb0d8$25d56e40$0401a8c0@xphd97xgq27nyf> From: "mal hamilton" To: References: Date: Mon, 10 Jan 2011 15:07:49 -0000 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2600.0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000 X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: LF: Re: Capacitor warning and First 500kHz Class E breadboard Content-Type: multipart/alternative; boundary="----=_NextPart_000_0044_01CBB0D8.259753D0" 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-sid: 3039ac1d411c4d2b211550df X-AOL-IP: 195.171.43.25 ------=_NextPart_000_0044_01CBB0D8.259753D0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable I designed and built a class E PA for 500 Khz when the band became ava= ilable. 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 fr= equency 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 si= nce.=20 My design is for 50 ohms and the TX is followed by a LPF then 100 yard= s of coax to the base of my inv L antenna. Antenna is also adjusted fo= r 50 ohms match. A class D amp is probably easier to build and needs no adjustments, ot= her than matching to the antenna. ie Class D is a broad band device whereas class E is specific to the= design frequency. g3kev =20 ----- Original Message -----=20 From: Andy Talbot=20 To: rsgb_lf_group@blacksheep.org=20 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 cla= ss E types.=20 Don't even think about using the small high voltage ceramic caps ava= ilalble at low cost from the suppliers - and sold as "suitable for SMP= SUs etc" in resonant circuits They are appalling, terrible, revolting things. You only have to br= eath 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 Clas= s E amplifier, (target design 500W from 50 V supply), calculated the= L/C values as per Alan's spreadsheet, combined with an L matched outp= ut for 50 ohm. For the capacitors I aimed to get within 5% of the cal= culated values using many of these small ceramic objects in parallel= - lots in || should share the current, shouldn't they, which would be= good? =20 So I soldered them up - used the G4HUP L/C meter to measure the valu= es - at which point I should have been a bit suspicious as the measure= d 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. =20 Anyway, made up the amp, used a 12V supply rail and monitored the sw= itching 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 coincidenc= e :-) =20 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 coefficen= t - 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. =20 I did have a just two trusted 22nF caps in the junk box that were wi= thin 20 - 30% of the right values for the amp and an awful lot of 3.3n= F 1700V things of a more respectable heritage, so just put these into= the circuit, tested at 12V and got waveforms almost correct. Increa= sed drive freq to 515kHz (no real scope for changing cap values at thi= s stage, so freq change would be easier to try with) where the wavefor= m 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/D= ownload/ClassE_BrdBd01.jpg =20 The yellow cap shunting the device was running quite warm - which is= hardly surprising just a single poly[whatever] carrying all those amp= s - 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 mo= stly-work immediately. Play with the drive frequency while monitoring waveforms to see whi= ch 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 ------=_NextPart_000_0044_01CBB0D8.259753D0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
I designed and built a class E PA for= 500 Khz when=20 the band became available.
I used some hefty poly caps in the PA= and never=20 used ceramic caps.
Use available caps to the nearest val= ue and to fine=20 tune pa, on the frequency of interest,  observing on a scope the= waveform,=20  tap the coil up or down a couple of turns until the correct wave= form is=20 visible.
This amplifier is very robust and &nb= sp;has given=20 excellent service ever since. 
My design is for 50 ohms and the TX= is followed by=20 a LPF then 100 yards of coax to the base of my inv L antenna. Antenna= is also=20 adjusted for 50 ohms match.
A class D amp is probably easier to= build=20 and needs no adjustments, other than matching to the antenna.
ie Class D is a broad band devic= e whereas=20 class E is specific to the design frequency.
g3kev
  
----- Original Message -----
From:=20 Andy=20 Talbot
Sent: Monday, January 10, 201= 1 2:22=20 PM
Subject: LF: Capacitor warnin= g and First=20 500kHz Class E breadboard

A warning to anyone contemplating making power amps - especiall= y class E=20 types.
Don't even think about using the small high voltage ceramic cap= s=20 availalble at low cost from the suppliers - and sold as "suitable fo= r SMPSUs=20 etc"  in resonant circuits
They are appalling, terrible, revolting things.  You only= have to=20 breath on them and they change their value.wildly
 
 
I've just  made up a first version of a breadboard for a= 500kHz=20 Class E amplifier, (target design 500W from 50 V supply), = =20 calculated the L/C values as per Alan's spreadsheet, combined= with an L=20 matched output for 50 ohm.  For the capacitors I aimed to get= within 5%=20 of the calculated values using many of these small ceramic objects&n= bsp;in=20 parallel - lots in || should share the current, shouldn't they, whic= h would be=20 good?  
 
So I soldered them up - used the G4HUP L/C meter to measure the= values=20 - at which point I should have been a bit suspicious as th= e measured=20 C was sometimes a fair bit lower than it should have been.  At= the time I=20 just put it down to "finger trouble" - one does tend to ignore littl= e things=20 like that sometimes.   
Anyway, made up the amp, used a 12V supply rail and monitored= the=20 switching waveforms, expecting to see something vaguely approaching= the half=20 sine on drains etc.
 
Results, terrible, nowhere near what they should have been - cl= early=20 summat was very wrong  I remeasured the || combination of the= caps -=20 after unsoldering they were sometimes as much as half the value= they=20 should have been  - until they cooled right down and approached= room=20 temp. Occasionally a cap value approaching correct would show up on= the meter=20 once in a while - but that was was probably just coin= cidence=20 :-) 
And yes, I did double, triple and quadruple check the meter aga= inst good=20 caps - it was OK every time.
 
These little blue things appear to have a huge temperature coef= ficent -=20 are completely useless, designed to do nothing of value, and all hav= e now gone=20 into the waste bin.
In fact, I was wondering if they were=20 random-capacitors.  
 
I did have a just two trusted 22nF caps in the junk= box that=20 were within 20 - 30% of the right values for the amp and an awful lo= t of 3.3nF=20 1700V things of a more respectable heritage, so just put these into= the=20 circuit, tested at 12V and got waveforms almost correct.  = Increased=20 drive freq to 515kHz (no real scope for changing cap values at this= stage, so=20 freq change would be easier to try with) where the waveform looked= best,=20 and increased supply volts.      Got= to 30V and=20 it was delivering 150 Watts; 40V and was getting around 350 Watts at= which=20 point I assumed it was going to work, so switched off= for a=20 break.   Wasn't going to tempt fate by gong to the fu= ll 50V=20 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 =20
 
The yellow cap shunting the device was running quite warm= - which is=20 hardly surprising just a single poly[whatever] carrying all those am= ps - and=20 the one in series with the tank was slightly warm.   = So, now=20 need to browse the Farnell catalogue (the cubic printed paper v= ersion is=20 easier) for some caps that will do the job properly - like more of= those=20 yellow ones.  Actually, may have enough of the 3.3nF ones, but= that would=20 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 probab= ly=20 mostly-work immediately.
Play with the drive frequency while monitoring waveforms  = to see=20 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
 
 
 
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