[Amps] SB220 power supply

[Steve Flood]

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