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Fisher MPX-WX

smittola

smittola

New Member
Hi All,

I am rebuilding another Fisher 500-B and have found a bad part in the FM MPX-WX. The bad part is the 38Kc coil inductor, Fisher part ZZ50210-33 (Z101 on the schematic). I have found what looks to be a replacement, Miller #1355. These are readily available on eBay.
Does anyone know if this is a valid replacement for the original Fisher part??


coil Info.png
 
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If it's center-tapped and resonates at 38 KHz (possibly with a different cap value), it should be fine.
 
Tom Bavis said:
If it's center-tapped and resonates at 38 KHz (possibly with a different cap value), it should be fine.
Click to expand...
Well, I finally found a rough schematic for the Miller 1355. I'm confused by the 1355 coil wiring vs. the Fisher ZZ50210-33? Can you offer any suggestions?
Below is a copy of both.
Fisher and Miller.png
 
The Fisher is a coil vs a transformer. Taking a guess at it, 2 on the Fisher goes to 1 on the Miller, 3 on the Fisher goes to 2 on the Miller. 5 to 5. Leave 3 and 4 on the Miller unhooked and with some luck it will work.

this really is a guess, so I don't know for sure if it will behave itself.
 
3 & 4 unused. The 3900 pF cap changes to 1500 to tune 38 KHz. If resistance measured 1 to 5 and 2 to 5 are equal or close, it's a center-tap and 1 & 2 are interchangeable. If not, it should be connected as the original, and you may not be able to measure that if it's open. In that case, somebody will need to measure a Fisher one - mine is hard to get to right now.
 
If 1 and 2 are reversed in phase from the original, it is possible that left and right channels could be reversed.
 
On the Miller 1355, the resistance between pins 1 & 2 is 26Ω. Pin 1 to 5 (tap pin) is 11Ω and 2 to 5 is15Ω. So, I assume the adjustment is not quite centered?
 
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that may just be an artifact of how its wound. If its multiple layers it could be centered AC-wise but because of the longer amount of wire on the outside of the coil the DC resistance might be uneven.
 
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