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Old 5th July 2010, 09:09 PM   #1
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Default question about the 866a

Ello

once again i am in need of your help.

i am thinking of using some 866a in my amp. they look great, and the near constant voltage drop is great compared to other tube rectifiers.

but i dont have the AC voltage on my PT to use a LC filter, and the 866a wouldnt respond well CLC with a ~50 cap as the first one.

but what if i used a NTC resistor in front of the CLC to reduce the inrush current? since that is the biggest problem with a cap that big. (as far as i can see...)

something like this one.
http://www.ametherm.com/Data%20Sheets/SL12%2090101.pdf

ofc i could just use some silicon instead... but would love a pure tube amp :-)
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Old 5th July 2010, 09:50 PM   #2
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You will also have to put up with the noise those mercury vapor jobs create.

I think I still have a pair of them in the closet or somewhere.
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Old 5th July 2010, 10:05 PM   #3
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Location: Madison, WI
I have been trying to incorporate them into my amp design but according to the specification sheet for one brand of that tube, a capacitor input filter causes continuous high current spikes during operation, not just a current inrush. Having too large of a capacitor in a choke input filter does cause just an inrush. My own simulations confirm this.
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Old 5th July 2010, 10:16 PM   #4
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#2
mhm.. that also.. might get some 3B28 instead... dont really know yet.. it is just that the 866a looks soo cool... (abit embarrassed, about making a choice based on astetic instead of performance....)

but with the 3B28 i will still have the problem described in #1

#3
ye i know, but some datasheets specifies upto 2A peak, and .5A continues current, when the voltage is down to 2000V (i will only be at 450.... but lets just use the data for 2000V since we have that) and with PSUdesigner, i wont have any spikes over 2A when the first inrush is done. then the spikes settle around 1.5A and 650mA RMS. and i use 2 tubes for fullwave so it doesnt seem like a problem.. though i dont really have any experince in this... so i might be wrong..

Last edited by heinrichs; 5th July 2010 at 10:31 PM.
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