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Message-ID: <007b01ca501a$3b319f40$0900a8c0@lark>
From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <AEFAF8DAD98D4571B7D80E689302E30E@IBM7FFA209F07C> <007201ca4ff9$cce15190$0301a8c0@mal769a60aa920> <8FD1DC2A56674846A459F7CD0ADB7468@IBM7FFA209F07C>
Date: Sun, 18 Oct 2009 15:35:32 +0100
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Subject: LF: Re: Re: Re: AF Amps at 136
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Chris try single ended Class-E very simple, ok they need a modicum of tuning
but have been used successfully by Mike GW4HXO and Finbar EI0CF and others
up to about 500W.  I have some notes on experiments at
http://www.alan.melia.btinternet.co.uk/classepa.htm
They are best operated at at least 24 volts and better at around 50, 60, or
even 75 with the right FETs.

Alan G3NYK

----- Original Message -----
From: "Chris" <c.ashby435@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Sunday, October 18, 2009 3:11 PM
Subject: LF: Re: Re: AF Amps at 136


Thanks for your comments Mal, I did wonder if such an approach was wise.
Let's see what others have to say on the matter. I also have my suspicions
about FETs in class D and the level of crud that could result.
Thanks again.
Chris, G4AYT.
  ----- Original Message -----
  From: mal hamilton
  To: rsgb_lf_group@blacksheep.org
  Sent: Sunday, October 18, 2009 2:49 PM
  Subject: LF: Re: AF Amps at 136


  Chris
  Do  not use audio amps for RF. Build a class D or E amp and operate
trouble free. Audio amps were tried by some in the early days but never
worked properly.
  Read the horror stories of yesteryears about using audio amps for RF
applications. Buckets of burnt out FETS.
  73 De Mal/g3kev

    ----- Original Message -----
    From: Chris
    To: RSGB LF Group
    Sent: Sunday, October 18, 2009 2:13 PM
    Subject: LF: AF Amps at 136


    Hi All,
    Just started constructing TX for 136kHz, noticed Maplin do a Velleman
audio PA kit that is rated at 200W (100W RMS into 4R). OK there's no mains
transformer or heat sink, but reckon it's good value at Ł14.99. Point is the
specs also say the minus 3db frequency response is 3Hz / 200kHz.
    The RSGB books 'LF Today' refer to using audio amps as PAs at 136 with
'a few modifications'. Does anybody know where these modifications are
documented? I guess there's nothing major, reduce a few cap values? Remove
Zobel Network etc.?? If anyone has experience with this approach I would
appreciate some hints. Thanks.
    Chris, G4AYT, Whitstable.


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