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Re: [Amps] Source for plate xfrmer

To: "Ian White GM3SEK" <>, <>
Subject: Re: [Amps] Source for plate xfrmer
From: "Carl" <>
Date: Tue, 14 Feb 2012 10:04:06 -0500
List-post: <">>
----- Original Message ----- 
From: "Ian White GM3SEK" <>
To: <>
Sent: Tuesday, February 14, 2012 6:38 AM
Subject: Re: [Amps] Source for plate xfrmer

> Rob Atkinson wrote:
>>In your long description you said nothing about the filter caps in use.
>>Please describe them.  Ideally I would want one or more oil caps giving
>>around 50 uF with 6 KVWDC
> Good regulation requires two things: low transformer winding resistances
> *and* sufficient capacitance. If the winding resistances are much too
> high (which seems to be the case with Steve's transformer) then even
> large amounts of capacitance can only have a marginal effect.
> This has always been apparent in the old paper charts, and software like
> PSU Designer makes it even clearer.
> 73 from Ian GM3SEK

This is where a choke input comes in handy. About 12H  (a fairly common 
surplus item) followed by about 20-30uF should give a stiff output at around 
90%+  of RMS.

Use a HV probe to check for diode spikes which can be mitigated by some more 
C and .01's across the each leg of the bridge and then another.01 to ground. 
You also need a bleeder resistor.

Maybe not as much voltage as you wanted but saves the $$ for more iron. I 
paid $40 for a 1A choke from a Gates 1000W+ BCB rig that was being scrapped. 
The RF finals and modulator ran off the same PS.
That amp runs 7  270uF 450V 105*C caps and the 2800VDC barely budges and 
spikes are all but gone but Im using plenty of 6A10's to be safe.


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