[AMPS] SB-220 C4 failure

[Rich Measures]

>> From:          km1h@juno.com (km1h @ juno.com)
>> Date:          Tue, 8 Jul 97 12:41:48 +0000
>
>> 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.
>
>That's correct Carl. Inrush was never a part of the concern. It 
>wasn't until 1970 or so that inrush became the curse of the 220, 
>causing arcs and pops and snaps and blowing out tubes.
>
What curse?  Says who?  Those who measured the SB-220's filament inrush 
current know that it is only 60% of what Eimac allows, thanks to Heath's 
special current-limiting filament. transformer.  At least two magazine 
articles discussed the subject.   

>In the 80's, it became fashionable to blame all the voo-doo science 
>claims of 70's inrush worries on parasitics. 

A connection between filament inrush current and parasitics?  Which 
article/author?  

>Hopefully in the 90's 
>and beyond we will stay with science, and put the batwings and eye of 
>Newt back in the footlocker.
>
During the vhf parasitics debate, Wes, N7WS, made scientific measurements 
of two types of vhf suppressors using a Hewlett-Packard Model 4191A RF 
Impedance Analyzer.  Mr. Rauch's response was to smokescreen Wes' 
measurements.  Those interested can read all about it in Will's (KN6DV's) 
archive.  
  
>The current limits because of the components internal ESR, which was 
>a natural result of the low power levels (1 kW ICAS INPUT power)  and 
>duty cycle (less than 50%) the 220 was designed for.  Same with the 
>filament transformer, any properly sized transformer combined 
>with the resistance of the filament choke, wiring, power line 
>ESR, and so on would limit filament inrush. There was no special 
>design, it was a conventional transformer.
>
I disagree.  The TL-922 has a conventional-core filament transformer that 
delivers 48A of filament inrush current to each 3-500Z.  OTOH, the 
filament inrush current in a SB-220 is 23.2A per tube.  This amount of 
current limiting can not be explained by the ESR in the filament circuit. 
  (according to Eimac, the max. allowable filament inrush current for the 
3-500Z is 29A)
- The filament transformer in the SB-220 appears to be similar to the 
design of current-limiting transformers used in neon signs. 
Rich---

R. L. Measures, 805-386-3734, AG6K   


--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm