[NJARC] Grill cloth question now fuses

[Aaron Hunter]

That would protect the outlet you're plugging it into, I'm not sure 
about the radio.  There is a certain amount of startup current drawn by 
the tubes until they warm up.  I don't know how much it is and you would 
have to allow for it or the fuse would blow when turned on.  You could 
use a slow blow, but I don't know if the transformer would be protected 
enough.  Maybe the lack of B+ on turnon offsets the excessive current 
drawn by the tubes.  I think this requires a study.  I have to stop work 
on my genealogy and get back to my radios and do some testing.  (without 
smoking the transformer, of course.)  The weak link is the high voltage 
windings.

I pulled out my tube manual to get an idea of current draw.  The tube 
filaments alone draw 38.125 watts in your radio.  But the part I misread 
on the rectifier is the DC current draw.  440 ma is the peak allowed on 
one plate with 125 being the max operating current. At 360 volts, it 
works up to 45 watts.   So my 1/2 amp fuse would probably allow for max 
smoke!  The tube might not pass enough current to blow the fuse and the 
winding is probably not rated much more than 2 or 300 ma.  A 2 or 300 ma 
fuse should protect the B+ winding at the center tap, but a 7/8 amp fuse 
at the line cord might not.  As I said, needs more study.

Any more thoughts on this out there?

Aaron

Edward Otte wrote:

>Aaron,
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>As far as the fuse, the only paper documentation inside the unit defines it
>as a 100W unit. That makes it about an 830 mA draw. Maybe a 7/8 would be a
>close match. But then again, I was thinking to fuse the input AC. Why is
>that not best? 
>
>Edward
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