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Re: [Amps] SB220 power supply

To: "Steve Flood" <>, <>
Subject: Re: [Amps] SB220 power supply
From: "jeremy-ca" <>
Date: Sun, 2 Mar 2008 22:17:05 -0500
List-post: <">>
Typical HV is 2500 @ 800 ma key down for 1100-1200W out on a stiff 240VAC 

They may not care for 48 hours of CW contesting in the SSB position but they 
hold up very well otherwise.

I see no reason why four 813's cant be used in GG at the same power level.

Added filter capacity wont do anything for key down readings. It may give a 
bit better SSB regulation; I use 330MF CDE 381LX caps as replacements in the 
SB-220 as they fit the blocks perfectly.


----- Original Message ----- 
From: "Steve Flood" <>
To: <>
Sent: Saturday, March 01, 2008 9:16 AM
Subject: [Amps] SB220 power supply

> To avoid having to build a separate power supply box, I am thinking of 
> using an SB-220 transformer.  As I see it, it was meant to run a pair of 
> 3-500's at about 2700volts and 700mA.   I am thinking of using it to run 
> either three or four  813's.  My calcs show about 170 to 180mA per 813 in 
> class B at 2700v, which tells me I am probably pushing the transformers 
> capability with four 813's.
>  An additional concern is the voltage drop on key down.  I read an online 
> article by K0GKD regarding the voltage drop and impact on linearity with 
> Heaths stock 25uF of filter capacity.  He increased the filter capacity to 
> 56uF and still noted a 10% voltage drop, but noted better regulation (??).
> If I end up with a voltage drop on key down or voice peaks, that tells me 
> the plate current will rise and further tax the transformer.
> So, my thought is the SB220 tranny may work well for three 813's but maybe 
> not with four 813s.
> Is my rationale correct?
> Steve, KK7UV
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