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Re: [Amps] GPT-750 power supply

To: "Steve Flood" <>, <>
Subject: Re: [Amps] GPT-750 power supply
From: "Carl" <>
Date: Thu, 9 Feb 2012 21:13:46 -0500
List-post: <">>
All you need for a choke is to get a bit past the "critical inductance" 
which is explained in all the old handbooks. Use more C at the output to 
reduce ripple.
I use a 12H 600ma choke also (must have been a popular surplus value) and 7 
220uF snap in caps for the C and it barely budges the HV in a 1000W final 
plus modulator. The transformer is from a 1000W Gates BCB TX that used 4 
833A's for RF and audio.


----- Original Message ----- 
From: "Steve Flood" <>
To: <>
Sent: Thursday, February 09, 2012 8:03 AM
Subject: [Amps] GPT-750 power supply

> I've been attempting to design a power supply using the big (100 lb) 
> TF-193
> transformer from a GPT-750 transmitter, the rating of which is 2800vdc @
> 750mA CCS, which is about what I'd like to get out of the supply for my
> intended ICAS use with CW and SSB only.  (No AM or RTTY)
> The transformer was designed for a choke-input and it has been a big 
> problem
> locating a suitable choke, particularly the actual 750mA 8-25H swinging
> choke used in the GPT-750.
> I have a few big chokes but none rated for 750mA.  The closest is a 12H
> smoothing choke rated 600mA CCS which would probably be fine for current,
> but the 12H is not enough inductance as it would only provide around 23%
> regulation (in combo with a 12uF cap and 30k bleeder) as I calculated 
> using
> (Duncan PS design software).  It seems I need something more like 25 or 
> 30H
> to get down below 10% regulation.
> So then, am I overlooking something in  this design,
> Or should I just consider selling/trading this transformer for something
> more modern for a capacitor-input supply?
> Thanks,
> Steve KK7UV
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