LF: Re: AF Amps at 136

["mal hamilton" <g3kevmal@talktalk.net>]

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 £14.99. 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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