I have a similar Peavey 1.3K with 90 V rails that has a diac-triac output shorting cricuit that tends to burn the PCB lands instead of trip the circuit breaker. I have a panel of Allen Bradley 100-A12ND3 contactors with 120 vAC coils, that I intend to use one of to break the output. I'm going to use the NC side so the relay coil breaks the arc, not the spring. These relays are rated 22 A @ 660 VAC so I hope it will break DC at 90 VDC. I'm going to use the standard Peavey 8v breakover diac with capacitor on the input to detect the DC on the output, but I'm putting the triac up front where it will be connected to the return of the power transformer input. To keep the Wall plug neutral away from the speaker return line on the output board, I'm going to use two optoisolators in parallel at the diac output with the input diodes set to detect DC one polarity or the other. Because the PIV of the junk optoisolators I have might not equal 90 VDC, I'm also going to put mr856 rectifiers in series with them, as well as the current limiting resistor. The output transistors of the opto isolators will trip the gate of the triac connected to the contactor coil, one polarity or the other. The opto outputs may need diodes too since the 120 VAC has 175 VDC peak. All the AC stuff will be up front except the relay, and it will only be powered if there is a problem. I'm going to use the third phase (contact) of the relay to latch it on if the fault goes away, and light an AC powered trouble lamp.
The cool thing about this relay it is small enough to fit between the output board and the back wall. The relay also has screw terminals big enough to accept the 10 ga wire Peavey used from the O.T. pcb to the output banana jacks. It also doesn't need an additional transformer to provide coil power. The Peavey transformer produces +-16 VDC but it is used on the op amp circuits, and shouldn't be used to power a relay.
If I get energetic I might design an RC timer circuit to parallel the opto triac drive to hold the relay on until a settle time has occured at power up.
I have some question about whether copper relay contacts would conduct at very low watts, but on this amp I doubt if that will ever occur. This amp uses too much power to run a speaker in the home at 1,5 V pp like I listen to music.
The cool thing about this relay it is small enough to fit between the output board and the back wall. The relay also has screw terminals big enough to accept the 10 ga wire Peavey used from the O.T. pcb to the output banana jacks. It also doesn't need an additional transformer to provide coil power. The Peavey transformer produces +-16 VDC but it is used on the op amp circuits, and shouldn't be used to power a relay.
If I get energetic I might design an RC timer circuit to parallel the opto triac drive to hold the relay on until a settle time has occured at power up.
I have some question about whether copper relay contacts would conduct at very low watts, but on this amp I doubt if that will ever occur. This amp uses too much power to run a speaker in the home at 1,5 V pp like I listen to music.
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some of the oxides of copper are very hard.
This may defeat the wiping/cleaning action of the electrical contacts.
Is that possibly why contacts are generally plated or are of different alloys?
These relays don't come apart for inspection or replacement of contacts, but the old GE replaceable contact contactors in this rating had a coppery looking contact. They were also about 10x bigger, with about a 1 cm diameter contact.The GE's did not have a lot of contact wiping action. I believe when AB introduced "euro" technology motor contactors, they speeded up the make & break to cut the contact and package size. I'm pretty sure these will still be copper based. Medium signals are supposed to be silver plated relay, Dry circuits without enough energy to burn any oxide are supposed to be precious metal plated.
I have a hundred of 1 A rated rhodium plated bifurcated contact telephone relays I'm collecting from a surplus house for an organ project, but I am quite sure they would be unsuitable for this service. I have a nice PM17DY that might work but it has a 24 V coil and would require a separate transformer and two transistors, not one triac. It is bigger than 4.5 cm wide, too, and I have a 6 cm space to fit things in against the banana plug buikhead.
Oh, anybody that buys these 100A-xx relays (all over E-bay apparently), get some relay mount track on the same order, because these will not screw to the wall without them.
I have a hundred of 1 A rated rhodium plated bifurcated contact telephone relays I'm collecting from a surplus house for an organ project, but I am quite sure they would be unsuitable for this service. I have a nice PM17DY that might work but it has a 24 V coil and would require a separate transformer and two transistors, not one triac. It is bigger than 4.5 cm wide, too, and I have a 6 cm space to fit things in against the banana plug buikhead.
Oh, anybody that buys these 100A-xx relays (all over E-bay apparently), get some relay mount track on the same order, because these will not screw to the wall without them.
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