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I have a 70s vintage circuit that uses a Triridge brand reed relay. It's marked with part number "220-100", and it's four pin, normally open. The operating voltage for the coil as seen in the circuit (and designed on the schematic) is 12V.

It's "sticking" closed when it's supposed to open sometimes (including with no power in the circuit at all), and I'm trying to determine why-- whether it's just old and been damaged from previous overcurrent excursions, whether it's under-rated for the current passing through it, some combination, etc.

I have been unable to find a scan of any data sheets or data books on eBay or whatever for this brand of relays. They seem to have made a ton of variants with often-confusing part numbers. I'd like to know what the voltage and current ratings actually are for the switching circuit.

Any pointers appreciated! Thanks.

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    \$\begingroup\$ Do you know what kind of a load the contacts are switching? Is it motor, amplifier, etc. Chances are unlikely of finding an exact replacement (and an identical one might do the same thing again.) There could be equivalents, but probably not in any handy index anywhere. \$\endgroup\$
    – rdtsc
    May 5 at 16:29
  • \$\begingroup\$ It's for switching an old cassette deck on and off via the "REM" jack. I haven't yet measured the current that the particular deck I have (which is contemporary to the control circuit) is drawing through that jack but I will. If the switch sticks with no power to the coil, is the relay definitively damaged/done? Or could that be a temporary symptom of poor usage? \$\endgroup\$
    – BZo
    May 5 at 16:39
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    \$\begingroup\$ In my experience, relay contacts tend to oxidize/corrode/melt/carbon-deposit over time and usage. This usually results in the contacts "sticking" in either the open or closed state. Sometimes, tapping on them lightly and exercising them will get them unstuck, but it is only temporary. Might work for a hundred times without incident, or just once then stick again. \$\endgroup\$
    – rdtsc
    May 5 at 16:45

2 Answers 2

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A quick web search finds a listing for a 220-100-24 that has a contact rating of 500mA resistive and 200V. Assuming they copied the numbers correctly, and assuming there is not some other additional designation for the reed capsule rating.

Reed relays are not famous for reliability when used to switch substantial current, especially if there's any inductance or surge current (or especially tiny currents, for that matter- my programmable ratio transformer warms up by clacking them all for several seconds). Sticking is a common failure mode.

If it's not a particularly picky circuit I would consider replacing it with a sealed telecom style relay. They're generally rated at 2A, which is far more than most small reeds can reliably switch. If it is a picky circuit, any similar size and rated reed will likely work.

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  • \$\begingroup\$ Thanks. Is sticking a temporary or permanent failure mode? As in, is it a symptom of poor use conditions now, or does it mean that something has happened in the past that will make it forever unreliable, regardless of its usage now? \$\endgroup\$
    – BZo
    May 5 at 16:44
  • \$\begingroup\$ (The -24 certainly seems to indicate a 24V variant versus the 12V mine uses. The coil resistance is different too, but either way that wouldn't impact switch-side max current specs, I suppose) \$\endgroup\$
    – BZo
    May 5 at 16:47
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    \$\begingroup\$ Sticking likely means the contact surfaces are worn out or damaged, so permanent. If it wasn't potted you could replace the reed capsule. Yes, the coil voltage should not affect the contact switching specs, but as you've noted their part numbers are not very specific. We would expect the coil power to be similar for 12V and 24V (288mW or so) . If yours are much higher than 500Ω that's possibly an indication the reed is rated for less current. Or not. \$\endgroup\$
    – Spehro Pefhany
    May 5 at 16:55
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I worked at Triridge in the 1970’s. 220 was the size and 100 was normally open contact and 12 was the coil voltage. Yes they are prone to failure. The company is no longer in business. There were many competitors try to find one.

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