Anyone hear built a drip LA2a

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Anyone hear built a drip LA2a

Postby andygriffiths » Tue Dec 17, 2013 11:48 pm

Hi all, I'm just in the middle of wiring up my Drip LA2a. I am just using 1 cell do I need to hook up the switch as if I am using 2? Also I'm using the LED VU meter instead of the normal lamp. Just wondering where I can get the power from? Last question for tonight what size fuse do I buy for the IEC connector?
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Re: Anyone hear built a drip LA2a

Postby Alastair Reynolds » Sat Dec 21, 2013 7:23 am

For the LED, 1/2 wave rectify a heater. Voltage then put the appropriate dropping resistor.Fuse wise 500ma or even 250ma should be more than adequate . if you,re only using a single cell a switch can be left out and wire directly
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Re: Anyone hear built a drip LA2a

Postby andygriffiths » Tue Dec 24, 2013 8:55 am

Thanks Alastair, is it a slow blow fuse? Sorry for my dumbness
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Re: Anyone hear built a drip LA2a

Postby Alastair Reynolds » Tue Dec 24, 2013 9:15 am

yeah, a T250mA should be OK, the in-rush current when the heaters are cold will be the biggest stress on the fuse , so a T /Timedelay/Slow-Blow fuse would be my choice here.
Fuse ratings are based on the continuous current that a fuse can carry without deformation of the fuse wire and premature failure. The fuse will open when the current exceeds approx. 1.6 times the rated current.
So a 1 amp fuse actually opens at 1.6A or there abouts. There may be some variations , but that's a good rule of thumb.
If a 1A fuse is carrying say 1.2 A, it will do it , but will eventually fail and when replaced with a 1A fuse will appear to be all OK.

Watch a fuse when you first apply power and heaters are cold or caps fully discharged if using a solid state rectifier, and see if the fuse wire flexes. if it does, it will probably fail prematurely.
Valve rectifiers, of course, come up gently and effectively "soft turn on" the HT.

Stay tuned for more obscure fuse -lore
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