Inrush current limiters ( ICLs)

[David C. Hallam]

I don't think inrush current limiting is too important with vacuum tube 
radios using miniature type tubes.  Inrush current limiters are 
resistors with a negative temperature coefficient.  If used you have to 
be careful were they are installed because of the heat they generate, 
not great but still some.

Line bucking transformers are another matter.  Line voltages today are 
commonly 10%+ of that when these BA's were designed.  Quite often 
components don't take too kindly to this increased voltage.  A 12V 
transformer set up for line bucking will drop the voltage back to the 
110V design voltage for old radios.

If you really want inrush current limiting, you can put a resistor and 
relay in the line bucking transformer set up.

David
KC2JD/4

Robert Groh wrote:
> I have started to do add inrush current limiting protection on almost all my restorations.  Particularly when I convert to solid state rectifiers and principally to cut down the huge current surge charging up the filter caps.  With a vacuum tube rectifier, you have the tube warm up time and characteristics which 'soften' the charging.  Not the same with solid state rectifiers - you get full rectified voltage pretty much right on turn on.  And, of course, softening the surge due to the filaments coming up to voltage doesn't hurt either.
> 
> Mouser has a couple of vendors supplying inrush current limiters:
> <http://www.mouser.com/catalog/catalogUSD/638/590.pdf>
> and
> <http://www.mouser.com/catalog/catalogusd/638/588.pdf>
> 
> If you follow the path through the Mouser site, you can find a link to the data sheets et al.  I think it is pretty good insurance.  With today's higher AC line voltages, we certainly have extra line voltage to burn.  Although adding a buck transformer to drop the line voltage would probably be a very good idea.  I haven't done that yet.
> 
> 73
> Bob, WA2CKY
> 
> 
> 
> 
> ________________________________
> From: Bob Jackson <bob at NOFROWNS.NET>
> To: BOATANCHORS at LISTS.TEMPE.GOV
> Sent: Monday, June 29, 2009 10:38:42 AM
> Subject: [BOATANCHORS-TEMPE] Inrush current limiters ( ICLs)
> 
> When restoring BAs (or any other vintage radio), is anyone here installing ICLs to protect tube filaments, etc.? I haven't been but am considering using small value thermistors for that purpose. My interests lie mainly in entry-level comm. radios a la Halli S-120 and similar.
> 
> Thanks,
> 
> Bob
> AG5X
> 
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