Typical HV is 2500 @ 800 ma key down for 1100-1200W out on a stiff 240VAC
line.
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.
Carl
KM1H
----- Original Message -----
From: "Steve Flood" <kk7uv@bresnan.net>
To: <amps@contesting.com>
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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