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Author Topic: Swan WM-1500 Diodes  (Read 1850 times)
WA3IIA
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« on: September 03, 2012, 10:24:34 AM »

Does anyone know what diodes are in the Swan WM-1500 Watt/SWR meter? I tried to locate a shcematic online but did not have any luck.
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WD8AJY
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« Reply #1 on: September 03, 2012, 10:33:07 AM »

The Swan WM-2000 uses 1N60s. Good chance yours does too.

73 Bob
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KA4POL
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« Reply #2 on: September 03, 2012, 11:47:17 AM »

I got a schematic here which says 1N914, all four of them.
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WA3IIA
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« Reply #3 on: September 03, 2012, 01:01:46 PM »

I pulled one of the diodes out and it has N596 stamped on it, which I am guessing is a 1N596. I checked to see if it crossed to a 1N60 or a 1N914 but it doesn't.  I have a pack of fifty 1N914's, I will replace all four and see what happens.

 Thanks
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K4DPK
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« Reply #4 on: September 03, 2012, 06:12:11 PM »

1N60s are germanium.  1N914 are silicon.  They have different forward voltage drops, 0.3 vs 0.6 and may affect the sensitivity and ability to properly calibrate the meter.

Measure the ones that are in there, since there's a chance not all of them are bad.  Then you can tell which to use.

Phil C. Sr.
k4dpk
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K4DPK
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« Reply #5 on: September 03, 2012, 07:24:52 PM »

Interesting....the 1n596 is a 1A silicon diode, much more robust than you would typically see in a simple RF sense circuit.

Anyway, the 1n914s will be fine.

Phil C. Sr.
k4dpk
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AC5UP
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« Reply #6 on: September 03, 2012, 09:26:27 PM »

Ten-Tec uses 1N914's in their SWR meters, which surprised me, while 1N60's are more commonly used. The 1N914 is a more durable Silicon part with a faster switching speed than the Germanium 1N60.  As K4DPK mentioned, the 1N60 does have a lower forward drop and would give better SWR sensitivity at QRP levels.

I like the Germanium 1N270 as it's a bit heavier than a 1N60, cheap and easy to find, plus I scored a buttload of them in a bargain box of parts tape acquired at a swap meet in the 20th Century. The diodes in an SWR meter are not particularly hi-spec, although I would use a diode tester to match the forward drop if I had a small pile to work with.........
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KA4POL
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« Reply #7 on: September 03, 2012, 09:51:49 PM »

According to the Motorola data sheet the 1N596 can be replaced by a 1N4005 which would justify the 1A current. However, the data sheet also says the surge current is 1A and the current would be 0.125A. This is similar to the Semitron data sheet calling for 150mA @ 25°C.
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WA3IIA
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« Reply #8 on: September 04, 2012, 08:17:51 AM »

I replaced the diodes with 1N914's and it works ok. The problem with the meter was when calibrating the meter on any of the power ranges the calibration would change when changing bands. I found two of the original diodes had a low resistance in the reverse bias direction. After changing all of the diodes I no longer have the problem.

I also found out that the original diodes were 1N5962, not 1N596. It just happend that the one that I first removed had part of the 2 scraped off.

Thanks for the help and comments.
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