[aeyb701]

Many high powered solid state amps of yesteryear, eg Crown DC300,  had no speaker protection relay against high DC voltages eg in case of a transistor failure. Just had my 1981 4B recapped by Bryston in Peterbough 3-4 years ago, but the thought didn’t occur at the time.
I have vintage Altec A-7’s and replacement horn diaphragms and woofer recones are expensive; been there (the fault of a Marantz 2270).
Reading up on the subject I see kits and assembled modules available with their own power supply, but others talk about wiring into the amp’s own power supply.
Relays must be capable of high current in these amps or the contacts could fuse.
I’ve read about fast-blow fuses but are they a guarantee against DC that might fry a coil but not blow the fuse?

Any one know of a reliable ready-made solution, please chime in. I can solder ( recapped my own vintage tube amp and receivers), oriented with tube schematics, but never delved into this here modern “solid state”.
Thanks
Jon Archibald
Peterborough Ontario

[sfraser]

I believe the 2 front LED's will indicate if any DC voltage is present on the outputs. Green means "good", and red means "run".

Scott

[aeyb701]

Hello and thanks for the reply.
I thought those were clipping indicators. Mike P. apprised me today that even their current units don’t have protection relays. Said not enough room in the early units anyway to retrofit.
I was more interested in those DIY outboard kits with own power supply. Not a prob if I can’t. Amp refreshed by Bryston recently.

[Rusty Jefferson]

If you're running that kind of solid state power into (especially vintage) speakers it's a smart idea to use a speaker protection circuit. I have a friend who designs/builds his own equipment and writes tech articles for Audioxpress magazine who just redesigned his speaker protection circuit for his quad-amp system and eliminated the relays. I know he recently had some circuit boards made for the project, I'll see if he has any available to share.

[richidoo]

https://neurochrome.com/products/guardian-86

[aeyb701]

Thanks for the link   
No room inside the 4B so either  wire to the inside mains terminal (half wave accordg to the block diagram: ac 60 volts?) by external leads, or could i use a wall wart in the specified input voltage range ( neutral common ground with amp at house service panel)?love the no-relay.
Thank you again
Jon A

[sfraser]

Hello and thanks for the reply.
I thought those were clipping indicators. Mike P. apprised me today that even their current units don’t have protection relays. Said not enough room in the early units anyway to retrofit.
I was more interested in those DIY outboard kits with own power supply. Not a prob if I can’t. Amp refreshed by Bryston recently.

You are correct, they are clipping indicators. The term "clipping" means a portion  of the output waveform has been "clipped" resulting in a high voltage DC signal being present on the output terminals. This is usually caused by exceeding the amp's voltage capability either via input gain or a voltage rail sag from a low impedance load on the output.

[Rusty Jefferson]

aeyb701, I checked with my friend this morning about his external speaker protection circuit. He does not have extra  circuit boards made however he will be publishing an article in Audioxpress magazine shortly about its design and construction as well as an article about his diy soft start control.

His design is more comprehensive than the linked one in that as well as preventing DC it also will prevent high frequency oscillations reaching the speakers and can be adjusted for a maximum power throughput, something that would be advisable with those Altecs. Keep a lookout at their website.

[aeyb701]

Thanks Rusty. I will watch/ look for it.
Jon