Return-Path: X-Spam-DCC: paranoid 1102; Body=2 Fuz1=2 Fuz2=2 X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on lipkowski.org X-Spam-Level: X-Spam-Status: No, score=-2.0 required=5.0 tests=BAYES_00,DNS_FROM_AHBL_RHSBL, HTML_30_40,HTML_MESSAGE autolearn=no version=3.1.3 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by paranoid.lipkowski.org (8.13.7/8.13.7) with ESMTP id u0AMXv5l003744 for ; Sun, 10 Jan 2016 23:33:57 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1aIOTF-0007a8-0P for rs_out_1@blacksheep.org; Sun, 10 Jan 2016 22:28:21 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1aIOTE-0007Zz-GP for rsgb_lf_group@blacksheep.org; Sun, 10 Jan 2016 22:28:20 +0000 Received: from out1.ip01ir2.opaltelecom.net ([62.24.128.237]) by relay1.thorcom.net with esmtp (Exim 4.86) (envelope-from ) id 1aIOSA-0005eU-CB for rsgb_lf_group@blacksheep.org; Sun, 10 Jan 2016 22:28:19 +0000 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: A2DOBADF2ZJWPKyNH1wNURkBAQEBEAECAgGERoZggXmjSpF6hg8CJYE7AQEBAQEBBwEBAQFBNIQ/AQEBAQIBI1sLCxgqAgIhIhQGCgmIGQMKriJxjFINgn8BAQEBAQEBAwEBAQEBAQEBAQEBGIhlgnCCT4FrG4MeLoEbBYdpg1eHUIQDi2GDVodthTJEgn6DMIdfhG5yhgYBAQE X-IPAS-Result: A2DOBADF2ZJWPKyNH1wNURkBAQEBEAECAgGERoZggXmjSpF6hg8CJYE7AQEBAQEBBwEBAQFBNIQ/AQEBAQIBI1sLCxgqAgIhIhQGCgmIGQMKriJxjFINgn8BAQEBAQEBAwEBAQEBAQEBAQEBGIhlgnCCT4FrG4MeLoEbBYdpg1eHUIQDi2GDVodthTJEgn6DMIdfhG5yhgYBAQE X-IronPort-AV: E=Sophos;i="5.20,549,1444690800"; d="scan'208,217";a="826950022" Received: from host-92-31-141-172.as13285.net (HELO [192.168.1.4]) ([92.31.141.172]) by out1.ip01ir2.opaltelecom.net with ESMTP; 10 Jan 2016 22:26:56 +0000 References: <15225aa896a-5493-6387@webprd-m74.mail.aol.com> From: Mal Hamilton X-Mailer: iPhone Mail (10B500) In-Reply-To: Message-Id: <4AFB43C9-91D5-4FC5-94EE-BEA169EE3B2C@talktalk.net> Date: Sun, 10 Jan 2016 22:26:56 +0000 To: "rsgb_lf_group@blacksheep.org" Mime-Version: 1.0 (1.0) X-Scan-Signature: 2bd5d3c3e4b1ac0d4c95b192e62a82a2 Subject: Re: LF: Re: [rsgb_lf_group] Linear Amp for LF Content-Type: multipart/alternative; boundary=Apple-Mail-B0714AD6-1B99-4016-AA98-898C2D3B6C57 Content-Transfer-Encoding: 7bit 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-Scanned-By: MIMEDefang 2.56 on 10.1.3.10 Status: RO X-Status: X-Keywords: X-UID: 6262 --Apple-Mail-B0714AD6-1B99-4016-AA98-898C2D3B6C57 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Andy I expect bias is around 5 to 6 V on gate G3kev Sent from my iPhone On 9 Jan 2016, at 22:13, Andy Talbot wrote: > Shortly after my original post on this topic I received two PMs, both poin= ting at a design by W7IUV for 400 Watts output, with a hint more is possible= , and that its robustness is proven in practice.. This was for use at 475= kHz but its design is broadband, so by choice of ferrite could easily span 1= 37 and 475kHz. I won't repeat the URL here as both responders chose to reply= individually with it, but if you Google (*) W7IUV something will show. >=20 > One reason this design appeals to me is the use of degenerative feedback f= ormed from multiple source resistors. In any amplifier design, using devic= es substantially below their maximum frequency - which is the case with swit= ching FETs at LF - some sort of feedback should, really, always be used. I= t will help with bias stabilisation, as well as keeping the overall design m= ore stable. MOSFET amps for HF nearly always apply NFB, often via a dedica= ted feedback transformer. >=20 > The G7IUV design shown doesn't give details of bias circuitry or PSU but t= hese are pretty standard for MOSFETs, although th euse of multiple parallel = FETs does ideally require that FETs be all from teh same batch to ensure mod= erate matching. >=20 >=20 > Andy G4JNT >=20 > (*) Other search engines are available (allegedly)=20 >=20 >>=20 >> On 9 Jan 2016, at 09:14, "David G0MRF g0mrf@aol.com [rsgb_lf_group]" wrote: >>=20 >>> =20 >>>=20 >>> Hi Terry. >>> =20 >>> Ask away...You have almost read my mind....... >>> =20 >>> I've been looking at the class D circuit in detail over the past few wee= ks....FETs obsolete....SWR detector not quite right etc. >>> I've even used it on its limits to make a nice QSO with SV on 630m last w= eekend. - Got so hot the snubber resistor on one of the drains fell off >>> =20 >>> I plan on producing around 50 boards if my Chinese manufacturer hasn't g= one bust in the stock market crash....=20 >>> However, I'm not sure the linear board has much sales potential as CW / W= SPR / JT9 can all be done with non linear amplifiers. >>> =20 >>> Also, the recently introduced power FETs are all optimised for rapid swi= tching in power supply applications. That's very different from 15yrs ago wh= en the Vg and Id transfer characteristics were much more 'linear' in nature.= >>> =20 >>> What do you think?? >>> =20 >>> David --Apple-Mail-B0714AD6-1B99-4016-AA98-898C2D3B6C57 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable
Andy
I expect bias is around= 5 to 6 V on gate
G3kev


Sent from my iPhone

On 9 Jan 2016, at 22:13, Andy Talbot <andy.g4jnt@gmail.com> wrote:

Shortly after my original post on this to= pic I received two PMs, both pointing at a design by W7IUV for 400 Watts out= put, with a hint more is possible, and that its robustness is proven in prac= tice..    This was for use at 475kHz but its design is broadband, s= o by choice of ferrite could easily span 137 and 475kHz. I won't repeat the U= RL here as both responders chose to reply individually with it, but if you G= oogle (*) W7IUV something will show.

One reason this desi= gn appeals to me  is the use of degenerative feedback formed from multi= ple source resistors.   In any amplifier design, using devices substant= ially below their maximum frequency - which is the case with switching FETs a= t LF - some sort of feedback should, really,  always be used.  It w= ill help with bias stabilisation, as well as keeping the overall design more= stable.   MOSFET amps for HF nearly always apply NFB, often via a dedi= cated feedback transformer.

The G7IUV design shown d= oesn't give details of bias circuitry or PSU but these are pretty standard f= or MOSFETs, although th euse of multiple parallel FETs does ideally require t= hat FETs be all from teh same batch to ensure moderate matching.
<= br>

Andy  G4JNT

(*) Other s= earch engines are available (allegedly) 
=

On 9 Jan 2016, at 09:14, "Davi= d G0MRF g0mrf@aol.com= [rsgb_lf_group]" <rsgb_lf_group@yahoogroups.co.uk> wrote:

<= blockquote type=3D"cite">
=20  
=20 =20

Hi Terry.
 
Ask away...You have almost read my mind.......
 
I've been looking at the class D circuit in detail over the p= ast few weeks....FETs obsolete....SWR detector not quite right etc.
I've even used it on its limits to make a nice QSO with SV on 630m = ;last weekend.  - Got so hot the snubber resistor on one of the dr= ains fell off
 
I plan on producing around 50 boards if my Chinese manufacturer ha= sn't gone bust in the stock market crash.... 
However, I'm not sure the linear board has much sales potential as CW /= WSPR / JT9 can all be done with non linear amplifiers.
 
Also, the recently introduced power FETs are all optimised for rapid sw= itching in power supply applications. That's very different from 15yrs ago w= hen the Vg and Id transfer characteristics were much more 'linear' in nature= .
 
What do you think??
 
David
 
 
= --Apple-Mail-B0714AD6-1B99-4016-AA98-898C2D3B6C57--