[AMPS] SB-220 C4 failure

[km1h @ juno.com]

>>Nothing wrong with the half wave rectifier in the 220...works
>>fine...lasts a long time. I dont believe in making extra work for 
>myself
>>particularly for no good reason. 
>>
>>73....Carl   KM1H 
>>
>For adding a step-start relay and high speed switching, a FWB is 
>indicated.  Half-wave rectification causes DC to unhappily flow in the 
>transformer.  Adding 3 more diodes  and ungrounding the 80v winding is 
>easy/inexpensive.  
>Rich---
>
>R. L. Measures, 805-386-3734, AG6K   

IMO, adding Step-Start to the SB-220 is a complete waste of time and
money. The filament  xfmr was designed to limit inrush current. The plate
xfmr is also current limited.  The power supply has other weaknesses that
have been discussed before:
	-  Undersized diodes that have been known to blow from power line
spikes. Replace with 1N5408's. 
	-  No air flow over the filter caps and made even worse by heat
generating equalizing resistors. Replace with the Harbach setup or
similar. 

The SB-220 is still a marvel of simplicity that has stood up well over
time despite a few shortcomings.

73...Carl  KM1H
>
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