I just ran across a local SX-1280 that somebody had done a middling decent job of cleaning the exterior. I tested for functionality (within the challenged environment) and it worked, but the relay cut out periodically when the volume was turned up to about 10 o'clock. The speakers were 90s current hog B&W's so I wrote it off to the dropping impedances as the woofer voice coils heated up.
That appears to have been somewhat true. At home with a pair of stock HPM-900s, they run fine, up to (and slightly beyond) an average level of 90wpc (on the meters, not measured at the outputs).
I have a heavily modified set of 40s, with a set of turn-of-the-century Polk Subs in place of the woofers whose nominal impedance is, I'm guessing @ 6 ohms. Ran as an individual set, they didn't trip the relay either. Running as two sets, (A+B, internally wired in parallel, unlike their later junk era receivers, which are wired in series) is where the relays start to open with gain at (or slightly above) the 10 o'clock position. I already know that the answer to all things 45 years old is to replace any cap that can't outrun one's soldering iron.
That's not my question. My question is, what's opening the relays? Or is the current load/increasing impedance from heated woofer coils, causing a thermal trip? Put another way, is this (approximately) about what you can expect from a restored (but not fully recapped) 1280? I have another 1280 that only runs a single set of the same modified, (cleaner tweeter and woofer) 40s and they (again, that one's been babied its entire life-it was bought in 2002) behave pretty congruently to one another. I bought this receiver as a backup for the other one, which I've used for twenty-two years in my bedroom system. Does this (especially when running two sets of a period/load-appropriate) behavior match what most folks see in their setups? I have a 1980 with two sets of 100s (stock) and it shoves (both sets) of those around without batting an eye or breaking a sweat. I very seldom get the presently installed 1280 up to an average 90 wpc. Usually, only when I'm in the shower, lol. I'm recovering from surgery and that makes it a little tough to wrestle either of these machines for the extended periods required for a PS recap. Maybe later, but not now. Any helpful insights are appreciated. I've finished the cleanup and I've replaced all the incandescent lamps with LEDs, and it looks "9-ish" so that part's done. TIA.
That appears to have been somewhat true. At home with a pair of stock HPM-900s, they run fine, up to (and slightly beyond) an average level of 90wpc (on the meters, not measured at the outputs).
I have a heavily modified set of 40s, with a set of turn-of-the-century Polk Subs in place of the woofers whose nominal impedance is, I'm guessing @ 6 ohms. Ran as an individual set, they didn't trip the relay either. Running as two sets, (A+B, internally wired in parallel, unlike their later junk era receivers, which are wired in series) is where the relays start to open with gain at (or slightly above) the 10 o'clock position. I already know that the answer to all things 45 years old is to replace any cap that can't outrun one's soldering iron.
That's not my question. My question is, what's opening the relays? Or is the current load/increasing impedance from heated woofer coils, causing a thermal trip? Put another way, is this (approximately) about what you can expect from a restored (but not fully recapped) 1280? I have another 1280 that only runs a single set of the same modified, (cleaner tweeter and woofer) 40s and they (again, that one's been babied its entire life-it was bought in 2002) behave pretty congruently to one another. I bought this receiver as a backup for the other one, which I've used for twenty-two years in my bedroom system. Does this (especially when running two sets of a period/load-appropriate) behavior match what most folks see in their setups? I have a 1980 with two sets of 100s (stock) and it shoves (both sets) of those around without batting an eye or breaking a sweat. I very seldom get the presently installed 1280 up to an average 90 wpc. Usually, only when I'm in the shower, lol. I'm recovering from surgery and that makes it a little tough to wrestle either of these machines for the extended periods required for a PS recap. Maybe later, but not now. Any helpful insights are appreciated. I've finished the cleanup and I've replaced all the incandescent lamps with LEDs, and it looks "9-ish" so that part's done. TIA.
Last edited:
