Fusion Message Board

In this space, visitors are invited to post any comments, questions, or skeptical observations about Philo T. Farnsworth's contributions to the field of Nuclear Fusion research.

Subject: Re: Diodes?
Date: Sep 23, 12:07 pm
Poster: Richard Hull

On Sep 23, 12:07 pm, Richard Hull wrote:


>All Electronics ( a surplus place in Van Nuys, CA (www.allelectronics.com) ) has 6kV, 200 mA diodes for $.50 each ($40/100). String 15 or 20 in series.
>If they are all from the same lot, the reverse recovery characteristics should match fairly well (which is responsible for most failures in a string, when one diode turns off before the rest).


Jim is correct here in that if the diodes are all the same recovery time to with a few hundred nanosends, maybe even a microsecond, then you might be able to get away with no resistors across the diodes. However the resistors guarantee that even if the cutoff occurs out of sequence then the voltage will still divide out properly and not blow your diodes. The resistors are very costly which provide this function, but worth it for headache free operation. Standard carbon comp. resistors are just not up to the task as they should not be burdened by more than 500 volts. However I have seen these work OK in some rare cases. I certainly wouldn't put them in OEM HV stuff though.

Finally, Like Jim, I place my strings in a length of 3/4" pvc pipe with a plug glued on one end which the lead goes through. I then fill the tube slowly with molten parafin (no air bubbles). A second end cap is glued onto the open end after the other lead is brought out. This arrangement has proven to be most satisfactory and inexpensive.

Richard Hull