# Varistor specs for LGB 1700 replacement



## birkman (Dec 21, 2019)

I'm cobbling together replacement contacts from old LGB 1700s with burned out reed switches. I'd like to build some using new components and have not figured out what the specs are on the varistor that is included in some models of the LGB 1700. Does anyone know what they need to be and where I can buy in small quantities?


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## Dan Pierce (Jan 2, 2008)

The 1700 is a unit with 1 reed sensor and 2 diodes. The center connection is common and feeds one side of the reed. The other side of the reed is connected to the diodes and each diode is connected to one of the end terminals. When A/C is supplied to the common, one end terminal gives a plus pulse and the other side gives a minus, thus enabling the output to 'switch' the EPL drive on a turnout.


This can be done with a sealed reed plus 2 diodes for as lot less $$ than what LGB sells.


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## birkman (Dec 21, 2019)

Thanks Dan,

In addition to what you've described, some of my 1700s have a varistor in parallel with the reed switch. That's the piece I am trying to find specs for. The 1700s with the varistor were smoother acting and I suspect, made the reed switches last longer.


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## Dan Pierce (Jan 2, 2008)

Could be a capacitor to minimize high frequency spikes. I used my 60 year old VOM on a low range and saw no resistance.


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## krs (Feb 29, 2008)

I have never taken an LGB 1700 apart, but are there absolutely no markings on that component?
It's a spike suppressor of some kind to protect the reed contacts when they drive an inductive load - I always thought it was an MOV but it couldalso be a capacitor.
Although a capacitor of that size would only be around 0.1 uf; I don't think that would do much to suppress the back EMF of the coil used in the LGB switch motor for instance.


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