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AUX high and AUX low connect to the same point on the input selector switch. AUX high goes through an attenuator circuit, which would explain the lower level. You could adjust the resistor values, or just use AUX-low since you said that sounds good. The tape input goes through a 150k series...

Unless it's literally falling apart, I'd just leave it alone. It's not like you handle it in normal use. If you really want to try to seal it, I'd leave it in place while you rub some high temperature adhesive into the crack. Silicone, or something like plaster, or ceramic tile grout should...

That is cutting it a little close with the fuse rating. I'd probably go with 2.5-3A. If the transformer had shorted turns, you'd know it because it would draw a lot of current, and get very hot.

My SX-82 is the same way. You have to switch it to mono when using the AM, or FM tuner in non-MPX mode. Some of these old receivers have features that work a little differently than we expect.

The phosphor does seem to be the weak link on the older round eye tubes with the metal target. The later 9 pin miniature eye tubes that have a horizontal bar display with the phosphor on the glass seem to last longer. A custom vacuum fluorescent display would be the closest modern replacement...

It should be fine, but since .0015 is a common standard value, there's no reason to substitute.

With a few wiring changes, you can turn the tape head input into a standard line level input.

It wouldn't take much. Just a direct connection between the hot AC wire and either side of the 5v output. It would still work fine as long as you didn't touch the output while you were grounded.

Then it's still not safe because a miswired outlet will make it be lethal. Either something is shorted, or it's badly designed. Normally, the power transformer is used to isolate the circuit from the power line. Everything on the primary side of the power transformer needs to be insulated...

It sounds like it's still an accident waiting to happen if it becomes lethal when plugged into a miswired outlet (hot and neutral reversed plus an open ground). That's easy to do if someone uses an extension cord with a missing ground pin, or if the ground pin on the plug breaks off. I know...

The tubes are all powered from AC on the S-8000 IV. It's just that the center tap of one of the heater windings is tied to the negative bias supply.

Speaking of strange design choices. My Sherwood S-8000 IV originally had the heaters for the preamp, driver, and output tubes tied to the negative bias supply. I disconnected this since it increases the heater to cathode voltage on all tubes, and a heater to cathode short in any tube would...

For the rare occasion when I need to solder aluminum wire, I use a product from Multicore called Alu-Sol. https://www.newark.com/multicore-loctite/alu-45d-4c-0-9mm-s-500g/solder-wire-alusol/dp/15J8243

I don't see a problem with reselling as long as the reseller adds some value. A clean, working, guaranteed item is worth a lot more to most people than an untested/broken item. People who restore these things for fun can easily forget how much their labor is worth. Just finding an honest...

You should be able to get away with removing the dust cap and shimming the voice coil while the glue on the spider dries. I refurbished a pair of those about 15 years ago, but the spiders hadn't separated. I just removed the excess padding, and massaged the cones back into position.

The mystery part is just a 1 uF 50v film cap. It's not likely to be bad, but you may want to replace the electrolytics. I would test any adhesives (other than water based ones) on a scrap of styrofoam. Certain solvents will eat through it very quickly.

Another option is an external Dolby digital decoder like the Technics SH-AC500D. It has several digital inputs so you can use devices that don't have a built in decoder.

Those caps are probably fine, but if you want to be sure, you can always take a look under the plastic top covers. Generally, caps from that era don't bulge at the top when they fail. If they did fail, they'd probably spew out so much stuff that the tops would have blown off completely. It's...

Call me crazy, but these speakers were made with standard off the shelf, non audiophile grade caps, and sounded good. Why not replace them with less exotic caps? Maybe they accounted to the higher ESR and other non-ideal properties of the original electrolytics when they designed the speakers...

I would just enjoy it while you can since you have no way of knowing what might, or might not fail on it. Interestingly, some people have successfully replaced laser diodes in old optical pickups. This means it's technically possible to rebuild unobtainable optical pickups without highly...

Some old CD players used a linear motor to move the optical pickup, similar to how a hard drive moves the heads. The result is almost instant disc access and track advance. I don't think and modern CD player works this way.

I usually use contact cement to bond the surround to the cone since it's instant, and it's next to impossible to properly use clamps for that. I like to gently push down on the cone with a weight on something hollow like a roll of tape while I position the surround. Then, carefully raise the...

I find that the most useful tests are ESR (internal resistance) and leakage current (at full rated voltage). Electrolytics develop increased internal resistance if they dry out. An ESR meter will let you test for this without removing the cap from the circuit (in most cases). If an amplifier...

Keep in mind that the lifetime number is when running at the rated temperature. All caps will last a LOT longer at normal temperatures. If the cap was running at 105 degrees, it would literally boil water on contact! Temperature isn't usually a problem for items like this. It is a problem in...

I've managed to save worse! I've almost finished restoring this ST-70 and will update my thread on it soon. It doesn't look new, but it's presentable, and works well. I highly recommend Dynakit parts. I replaced all of the screws, jacks and switches with their parts.