[AMPS] SB-220 C4 failure

[km1h @ juno.com]

On Mon, 7 Jul 97 22:30:12 -0700 Rich Measures <measures@vc.net> writes:
>>
>>On Mon, 7 Jul 97 11:06:57 -0700 Rich Measures <measures@vc.net> 
>writes:
>>
>>>>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.  
>>
>>>...snip...
>>>- The HV transformer is required to produce repetitive, high peak 
>>>currents to satisfy the considerable demand of the C-filter.  If the 
>
>>>HV 
>>>transformer were designed to limit current--like the 220's filament 
>>>transformer--the HV regulation would be unacceptable. 
>>
>>I did not say that the xfmr was designed to limit current, I said it 
>was
>>current limited....there is a big difference between the two. 
>> 
>...and the big difference is?

Rich, Bill, etc

The big difference is the word "designed".  I dont believe that the Heath
engineers were overly concerned about PS inrush current. It wasnt a
marketing hype word back then. 
The SB-220 plate xfmr is only rated at 1000VAC @  800ma and I even doubt
that is CCS. The internal impedence or whatever you care to call it just
naturally limits the surge. Note that the 220 does not exhibit the groan
when powered up as do many other amps with heftier xfmrs.

Then again maybe Heath knew exactly what they were doing. When other
doubler supplies of that era were using 80-100MF caps, Heath opted for
200MF each. Was this a conscious decision to limit the iron and still
provide peak power for SSB? The FCC limit was only 1000W input on CW back
then.  
The very heavy bleeder string also tends to limit inrush current.

Just something to chew on.

73....Carl   KM1H

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