LF: AF Amps at 136

[Lubos OK2BVG <bvgbob@hotmail.com>]

Hello friends!
I use AF amp Hafler on 137kHz and it works without problems. W1WD inspired me, so I bought Hafler P3000 via e-bay in USA. But it is true, that I have never trayed to use other typ than Hafler.

Lubos, OK2BVG

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From: jrusgrove@comcast.net
To: rsgb_lf_group@blacksheep.org
Date: Sun, 18 Oct 2009 10:59:36 -0400
Subject: LF: Re: Re: Re: AF Amps at 136

Chris

 

See links below...audio amps used on LF, MF. These Hafler amps were selected because they are rated to 300 kHz right out of the box. Probably won't find similar performance in very many amps. I only use the Haflers for modes requiring linear amplification - otherwise I run a class D setup.  

 

http://www.w1vd.com/page21.html

 

http://www.w1vd.com/page23.html

 

http://www.w1vd.com/9505MF.html

 

Jay W1VD  WD2XNS  WE2XGR/2

----- Original Message -----

From: Chris

To: rsgb_lf_group@blacksheep.org

Sent: Sunday, October 18, 2009 10:11 AM

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 £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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