From: "Clemens Paul" <cpaul@gmx.net>
To: <rsgb_lf_group@blacksheep.org>
References: <791401561.20170803151834@gmail.com>
In-Reply-To: <791401561.20170803151834@gmail.com>
Date: Fri, 4 Aug 2017 14:10:32 +0200
Message-ID: <C0B5249881FC460BA529228D1E0842AD@Clemens0811>
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Subject: LF: RE: LPF for a valve based (tube based) LF amp?
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Hi Chris,

at the risk to state the obvious:
A LPF of a solid state PA has 50 Ohms in- and output impedance.
A tube type PA needs a LPF which transforms from several kOhms on the tube side
to 50 Ohms at the output.
Therefore the values for the lumped reactances differ considerably from the non-transforming LPF.
Moreover design parameters like optimum loaded Q for the needed flyweel effect etc. come into play.
The ARRL Handbook,also old versions, cover this subject in depth.


73
Clemens
DL4RAJ 
 

>-----Original Message-----
>From: owner-rsgb_lf_group@blacksheep.org 
>[mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Chris Wilson
>Sent: Thursday, August 03, 2017 4:19 PM
>To: rsgb_lf_group@blacksheep.org; rsgb_lf_group@yahoogroups.co.uk
>Subject: LF: LPF for a valve based (tube based) LF amp?
>
>Hello LF'ers,
>
>
>My next contemplated project is a GS35B valve based LF amp. I have the
>HT supply, a couple of GS35B's to play with and a suitable filament
>supply. My question is can I build an air wound LPF based on exactly
>the same values as the one I use on my W1VD FET based Class D amp?
>That gets pretty warm and I use a small PC processor fan on the centre
>toroid, but I am unsure if the filter characteristics are specific to
>a FET based amp in some ways?
>
>W1VD  amp  schematic here: http://www.w1vd.com/137-500-KWTX.html    (1
>kW amplifier) http://www.w1vd.com/137-500-KWRev3.0.pdf
>
>
>
>W1VD LPF details here:   http://www.w1vd.com/LPF.html
>
>http://www.w1vd.com/LPF.pdf
>
>  
>
>-- 
>Best regards,
> Chris                          mailto:dead.fets@gmail.com
>
>
>
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