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abj1 15th March 2005 01:16 AM

Minimum current for choke operation
 
Hi All,

Does anyone have any idea of the minimum current needed for significant inductance from a choke. Say, for arguments sake, I wanted to use a choke with nominal ratings of 6H at max current of 60mA - what rough proportion of the max current would give me useable inductance for power supply filtering purposes? Thinking of using such a minibeast at around 6 to 8 mA (ie close to max ratings for use after 6H6 FW rectification - so I couldn't really supply it with much more current than this....)

Cheers,
Andrew.

Sch3mat1c 15th March 2005 02:41 AM

Inductance usually goes down with greater current. There does not need to be a static current for inductance.

FYI, I've ran a 6AL5 (miniature 6H6) at some 50mA in a flyback converter... that was interesting. :D Tube didn't grunt or anything either...

Tim

abj1 15th March 2005 03:22 AM

Thanks Tim,

I was hoping for such a reply! Mmmm 50 mA from a 6AL5 - more than I would have tried but what the heck!

The ratings for 6H6 are quite a bit lower than for 6AL5 - do you consider them to be overly conservative given that the 6H6 is not usually used for power rectification? (I currently use a pair of 6H6's in a FW bridge from a cheapo 12-0-12 tranny to supply negative grid bias in a CLC configuration for a stereo push-pull amp and am looking to do so for a single ended project which is almost complete). My concern is probably unfounded but I've been a bit concerned about the performance of a choke designed for larger currents (ie old relics from a wrecked radios - probably rated for around 60mA or so) at such low currents. However, based on your experience with the 6AL5, I'm feeling cheeky enough to try higher currents and see how it all performs..... The current amp performs well enough with the choke seeing around 8mA.... but maybe could be better.... :)

Cheers,
Andrew.

planet10 15th March 2005 07:49 AM

Quote:

Originally posted by Sch3mat1c
FYI, I've ran a 6AL5 (miniature 6H6) at some 50mA
An interesting use for all thos 6AL5s i have...

dave

Sch3mat1c 15th March 2005 04:45 PM

It's rated for 330 PIV, 9mA or whatever per diode, so you can safely draw 18mA at 170VDC. My flyback was running maybe 100V, a far cry from 330V, so I can't comment on that rating. It was only a breadboarded circuit to which ratings do not apply, but heck, who cares-- 6AL5s are quite literally dime-a-dozen. Probably one or more e-Bay auctions right now selling a bag of them as xmas tree lights.

That said, I'd like to see what the true PIV is. If it goes as high as 500 or 800V, a bunch paralleled could be a cheap alternative to the 5Y3 and 6X4.

Tim

planet10 15th March 2005 07:52 PM

Quote:

Originally posted by Sch3mat1c
selling a bag of them as xmas tree lights.
I probably have 1/2 a bag... do you know what the voltage drop across them is?

What sprung to mind 1st was a dual FW bridge for a pair of trafos i was going to use to generate ~ 70-0-70 for the tube stage in the tube beffered IGC....

dave

Sch3mat1c 15th March 2005 10:39 PM

Datasheet says 10V @ 50mA. Not RMS so figure maybe 1/2 to 1/4 current to account for power factor. That means maybe 10V drop at 20-30mA from one tube!

Oh, since PIV is low and the cathodes are independent, a FW doubler would be better. That'll get you up to PIV volts out, instead of only half for a standard FW circuit.m Anyone for 300V at 100mA from five of these little things*?

*Why is bug-gers askeriskized anyway?

Tim

jeff mai 15th March 2005 10:58 PM

Quote:

Originally posted by Sch3mat1c
*Why is bug-gers askeriskized anyway?

It was a naughty word about 100 years ago. The naughty word software must have been born in 1880.


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