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SPEC 4 Soft Start Relay Arcing

C

Colleton

AK Subscriber
Subscriber
When I bought this SPEC 4 it had some issues - a physically cracked right channel amp board and a soft hum coming from the soft start relays. I repaired and rebuilt the amp boards and replaced the filter caps. It sounded great and seemed to work well, but the hum from the soft start relays got louder and louder over time. This was a scary job for me, but I sacked up and replaced the soft start relays. Sounded great, looked great, worked great. There was much rejoicing.

A few months later...

The amp still sounds fantastic and works reliably every time I turn it on, but I noticed something... There is a small arc inside the front soft start relay at turn on. Is this normal? I wouldn't think so, and I don't believe it was there immediately after the relay replacement. There is no audible hum or noise from the relays. Any ideas on what might be causing this and what I can do about it? Should I add small magnets to the sides of the relay case? I've retired the amp from use until I can figure out what to do.

Thanks in advance for any thoughts and help, I appreciate it.
 
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Colleton said:
When I bought this SPEC 4 it had some issues - a physically cracked right channel amp board and a soft hum coming from the soft start relays. I repaired and rebuilt the amp boards and replaced the filter caps. It sounded great and seemed to work well, but the hum from the soft start relays got louder and louder over time. This was a scary job for me, but I sacked up and replaced the soft start relays. Sounded great, looked great, worked great. There was much rejoicing.

A few months later...

The amp still sounds fantastic and works reliably every time I turn it on, but I noticed something... There is a small arc inside the front soft start relay at turn on. Is this normal? I wouldn't think so, and I don't believe it was there immediately after the relay replacement. There is no audible hum or noise from the relays. Any ideas on what might be causing this and what I can do about it? Should I add small magnets to the sides of the relay case? I've retired the amp from use until I can figure out what to do.

Thanks in advance for any thoughts and help, I appreciate it.
Click to expand...
I would say it is probably normal. The relay allows for the turn on surge(s) to be staggered. When you flip the switch transformer T2 is immediately powered on, creating surge one as it charges up two of the four large value filter caps.

A short time later the relay engages providing power to transformer T1 which creates the small arc you see when the transformer is energized and pulls another surge (2) of current to charge it's pair of caps. I suppose over x number of on/off cycles the relay contacts will become pitted and possibly fail, just like a lot of power switches that no doubt have a little bit of arcing as well.

FWIW in my mind that is not a "traditional" soft start circuit, it is a staggered start circuit. There is no limiting device for the inrush current to either transformer, just a short delay between the first and second transformer being energized.
 
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Colleton said:
Okay. It would be nice if it is normal. Thanks.
Click to expand...
it may or may not be of interest to you but xraytonyb did a 5 part series on the spec 4 and modded it with a true soft start circuit. . . i THINK that he has the circuits available to his patreons but i can not remember for sure. he may mention in one of the videos but again, i can't remember.

www.youtube.com

xraytonyb

Videos and information related to Electronics, Vintage Electronics, Repairs, Projects, etc. There may also be info about woodworking and any other hobbies/interests I may wish to share. From time to time, I may share some information about medical imaging equipment operation and repair.
www.youtube.com www.youtube.com
 
Spec 4 has two e-i square transformers, rather than toroid transformers that NEED soft start.

The square transformers saturate magnetically at say 600 watts surge, and the relay contacts do take some punishment

YOUR relay's contacts are probably pitted and burned from long use and are calling for replacement.

ASR-041, 120 vac coil, replaced by mouser's 653-LY2F-AC1 - a DPDT relay, mfr part # LY2F-AC110/120 - this should help you find equivalents

You will probably mount it with four 15mm long 3mm x 0.5mm male-female threaded standoffs.

Using a two sets (DPDT) of contacts relay, tie the sets together in parallel for longer life.

Search this forum for "ASR-041," for more pointers in the found threads as there WILL be some fiddling to mount it, as that mount style case is NLA.



chassis mount using upper ears
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
to mount this relay use standoffs (mouser.com parts numbers) 15mm M-F aluminum (stainless steel preferred),
need two per side for 30mm: 728-FM2110-3005-A due to the ears being on TOP instead of on the bottom of the case.!

728-FM2110-3005-SS stainless steel preferred standoff 15mm long(need two per side):
728-FM2110-3005-A is 4.5mm od 3mm x 0.5 thread 15mm male female aluminum
728-FM2110-3005-SS is 4.5mm od 3mm x 0.5 thread 15mm male female stainless steel
728-FM1262-3005-A is 4.5mm od 3mm x 0.5 thread 15mm female female aluminum

Standoff.png
 
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A cheap and easy method, but still very effective modification is to strap .01 mfd. 1kv ceramic disc caps across each set of relay contacts.
Doing that will squelch/snub any arcing caused by inductive/capacitive kick back, just like what the cap does that is used in old style ICE points type ignition.
 
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