[Amps] Re: [HomeBrew] Need some help!

GGLL nagato at arnet.com.ar
Mon Feb 16 20:10:41 EST 2004

	After reading some justified mails complaining about answering to the 
sender and not to the list (12V, 50W zener ID), I repeat my answer to 
this forum, although the question was posted at Homebrew list (and 
replied there). Below is my answer to Ron.

Best regards
Guillermo - LU8EYW.


    Hello Ron, I do not figure out why that test gave those different
results (if one try with different VOM's it could be reasonable, but
with the same...).
    You can try to build a simple test fixture with a variable power
supply, a voltage dropping resistor and a voltmeter across the zener;
for example, an up to 20 V variable supply, (+) supply lead feeding  two
100 ohms 2watts paralleled resistors in a series arrangement with your
"X"  zener diode and attach then the free end of the zener to the (-)
supply lead.
    Put the voltmeter across diode terminals, positive lead to the
resistor/zener joint, the VOM negative lead to the supply (-) lead and
zener joint.
Rising up the voltage slowly you may note either of two things (if
diode is fine); no matter how much you bring up the supply volts the
measured voltage across zener stays at 0.6...1 V, if so, you have the
Anode connected at the positive VOM lead and consequently the Cathode at
the negative VOM lead.
    The other case is that if you rise suply volts until you reach the
vicinity of suspected zener voltage (12V in this case) then it must
stabilize around that value, no matter how far beyond 12 V you rise the
supply volts. Being this case, you have the Cathode at the positive VOM
lead and the Anode at the negative VOM lead.

Well it's a somewhat large explaining text, but hope it is clear for you
and so be useful.

Best regards
Guillermo - LU8EYW.

w2cqm at juno.com wrote:

>** Please do NOT cross-post messages to multiple mailing lists on the "To:" or "CC:" line of the e-mail message. **
>I have a SK550 (918) zener diode that I believe to be  rated at  12VDC @
>50W.  There appears to be ( barely visible) an arrow pointing away from
>the metal threaded housing towards the cathode end.  When tested with the
>VOM on the diode scale, it conducts (value of 770)  with the  negative
>(black)  lead on the metal base and the positive lead on the insulated
>end.  No meter  indication when the leads are reversed. So far so good!  
>What concerns me is that I checked it with another Western Electric 
>zener diode clearly identified with numbers and symbols  and the
>positions of the two VOM leads must be reversed in order to get it to
>show a value. In this test, the red lead (+)  is on the base and the 
>negative  lead  is on the output end ( direction of arrow ) . This
>particular 50w zener was working fine on a two hole 8877 I built some
>time ago;however, I pulled the zener to do some extensive bias  rewiring
>and cannot recall how it was originally wired. The question is basically
>which orientation should I use. Follow the arrow or reverse the diode and
>follow the wiring scheme dictated by the VOM . Is there anyone familiar
>with the SK550 in order to:
>	A. verify its identification?
>	b.  help get the orientation correct?
>	For obvious reasons,  I'd rather not use the cut and try approach. Any
>help would be appreciated. Dealing with lots of power so I want to ensure
>I get it right the first time. Ron W2CQM/3
>HomeBrew mailing list
>HomeBrew at mailman.qth.net

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