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Question about replacing relays

You definately will find a lot of general purpose relays measuring a few ohms if left on the shelf for ten years, resistance goes low again when putting an Amp of current or so through it.
If it is not oxides, it will be moisture buildup over the years, in the end any temp change will get air in or out.

If needing no specific contact arrangement (read: when ADDING a protection relay) I help myself with "vintage" sealed relays I scavenged from some never used equipment, so I can not see the contacts :D:D
I used LRE brand M300-D2A for my old Sansuis not having a protection relay before.


Now, for the general purpose relays to remain their low contact resistance, if using sealed PLASTIC ones, one has to observe that the sealing remains closed. Especially then, as @Skywatcher pointed out, high voltages and currents at the moment of "music present" when switching on or off, are the enemy.

Whether you have to pinch the hole or not, read here https://www.te.com/commerce/Documen...g_Sealed_Relays_AppNote&DocType=CS&DocLang=EN
 
gslikker said:
You definately will find a lot of general purpose relays measuring a few ohms if left on the shelf for ten years, resistance goes low again when putting an Amp of current or so through it.
If it is not oxides, it will be moisture buildup over the years, in the end any temp change will get air in or out.

If needing no specific contact arrangement (read: when ADDING a protection relay) I help myself with "vintage" sealed relays I scavenged from some never used equipment, so I can not see the contacts :D:D
I used LRE brand M300-D2A for my old Sansuis not having a protection relay before.


Now, for the general purpose relays to remain their low contact resistance, if using sealed PLASTIC ones, one has to observe that the sealing remains closed. Especially then, as @Skywatcher pointed out, high voltages and currents at the moment of "music present" when switching on or off, are the enemy.

Whether you have to pinch the hole or not, read here https://www.te.com/commerce/Documen...g_Sealed_Relays_AppNote&DocType=CS&DocLang=EN
Click to expand...
Using sealed relays would be great, if they were available to "drop-in" without modifications. But for "customizing" they would be the Cat's Meow. I often contemplated doing so. Humidity plays a role in virtually everything. However, it won't directly attack new point surfaces. Air quality in storage environments play a big role there too. BUT since those "old but new" relays aren't sealed, pop the cover and run a piece of paper across the points to wipe off the accumulated film layer. You'll find the resistance will drop to zero. If they were stored near "salt air", all bets are off. :D The points may not be bad, but the other metals might take 'er tough. I've had some Panasonic/Matsushita relays with "perfect" points, that still had resistance. The attachment point of the points themselves to the metal wasn't so good. If I squeezed them together hard enough, resistance dropped to zero. So I "deep sixed" them...
 
gslikker said:
Now, for the general purpose relays to remain their low contact resistance, if using sealed PLASTIC ones, one has to observe that the sealing remains closed. Especially then, as @Skywatcher pointed out, high voltages and currents at the moment of "music present" when switching on or off, are the enemy.

Whether you have to pinch the hole or not, read here https://www.te.com/commerce/Documen...g_Sealed_Relays_AppNote&DocType=CS&DocLang=EN
Click to expand...
Good point. On most, if not all "consumer grade" appliances (including audio) the vents are not sealed. Even on most "commercial grade" NOT used in environments where a spark could cause an explosion, the vents are not sealed. They do that for 2 reasons. 1 being "eliminate a step to pinch pennies", and 2 being "built-in self destruct" so people have to either pay for repairs, or buy "new" again after certain lengths of time. I just went and looked at a lot of boards with relays from stoves/ranges, dryers, washing machines, refrigeration, both domestic and commercial types. NONE of the vents are sealed on the "sealed" relays.
 
I once had the fortune to work with relay manufacturers to find a cheap(ish) relay
for a consumer electronics product that had a horribly high start current. The relay
in itself is not interesting but we learned a lot during the process. Autopsies of dead
relays were compulsory and checking the worn contact surfaces under microscope
guided the necessary changes of our own design and of the relays. How and where
the contact metals move on and between the contacts give clues to the cause.

The mechanics of how contacts move is also part of the designs. Sliding surfaces
keep clean but also cause quicker wear, low level switching uses this but a thin
gold plating is not enough, massive gold alloy contacts are used in microwave relays
good for 10 GHz and more (and they cost more than fancy stereo equipment).

Seeing odd stuff from non-audio areas helps in realising how many different factors
influence relay designs. Mercury wetted relays is one and hermetically sealed, inert gas
filled high tech designs is another.
 
FinalVinyl said:
been using same Omron "general purpose" relays for 10 years without any problems at low and high volumes. Any improvement with audio relays is negligible.
Click to expand...
Just like "General Purpose" capacitors. Most meet, or exceed the performance of "specialty" capacitors of yesteryear. Point being just because a relay is classified as "General Purpose", doesn't mean it won't "meet or exceed" the performance of the original for a given duty. For speaker protection, the Omron GP meets the criteria. Although other brands such as Schrack work just dandy too.
 
I wonder if the engineers over at Synergistic Research have some special quantum tunneling relays on the drawing board...directional, of course.
 
This is what the relay contacts look like in a NEC MR72A-24U (from a NAD 3400).
Symptoms were erratic speaker levels and since replacements are arriving soon
I cut the old (bad) one open, the other relay was OK but B-speakers probably never used.
At best the contact resistance was 30-40 milliOhm and up to several Ohms
changing with every activation.

Contacts are not burned the same way as in hosuehold appliances where the
surface can look like the Himalayas when they finally give up. The worn spot
could easily be polished IF you could get into the relay which you can't. The
barriers inside for high voltage insulation makes that impossible.

NAD_NEC_relay.jpg
 
Stepwise said:
This is what the relay contacts look like in a NEC MR72A-24U (from a NAD 3400).
Symptoms were erratic speaker levels and since replacements are arriving soon
I cut the old (bad) one open, the other relay was OK but B-speakers probably never used.
At best the contact resistance was 30-40 milliOhm and up to several Ohms
changing with every activation.

Contacts are not burned the same way as in hosuehold appliances where the
surface can look like the Himalayas when they finally give up. The worn spot
could easily be polished IF you could get into the relay which you can't. The
barriers inside for high voltage insulation makes that impossible.

View attachment 1934053
Click to expand...
Very cool and informative thanks.
 
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