[Top] [All Lists]

[Amps] SB220 power supply

To: <>
Subject: [Amps] SB220 power supply
From: "Steve Flood" <>
Reply-to: Steve Flood <>
Date: Sat, 1 Mar 2008 07:16:19 -0700
List-post: <">>
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 

  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
Amps mailing list

<Prev in Thread] Current Thread [Next in Thread>