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Here's an EBAY link for the switches I used. EBAY link To clarify the listing appears to be the same as what I used. Have to be careful using a switch on the bleeder resistor. Contacts rated for 100 volts DC are rare. I don't have a switch on my bleeder.

A few things to consider: Ideally, the fins would be facing inside so the fans push air across them. A switched 1:1/10:1 voltage divider that feeds the scope. The first time I did that I used 1k and 10K. WRONG! 10K and 90K or some multiple of that. You mentioned you will have two monitor...

Unlike electrolytic caps, which becomes open as the electrolyte dries out, the failure mode of tantalum is a short. The attached document discusses tantalums on page 5.

Yep, same here. That is one of few exceptions to my rule that semis are run to fail. I see people buying these repair kits on EBAY and change out every transistor and diode. Changing out diodes and transistors that haven't failed does not improve reliability. The potential damage to the...

Did this thing take on water? Otherwise, it's not common to see rust on transformers. The Luxman I'm working in has the same glue/resin all over the place. I don't think it's glue because the same gunk is under 1/4 watt resistors. There is none under the electrolytic cap, just around the...

One of my post retirement gigs is doing repairs (amplifiers/receivers) at Stereo Lab in Columbus Ohio. Although the facility is relatively large, consoles take up a lot of space so I usually pick up the unit, fix it at home and drop it off when it's done. What's wrong with these photos...

The data sheet tells it all. Who knows what it sounds like, but it does protect itself.

As one of my post retirement jobs, I'm doing repairs here and there for a local shop, Stereo Lab, In Columbus Ohio. Many years ago there were Japanese data manuals for semiconductors. One that is very beneficial for vintage gear is the Transistor Substitution Manual. The latest version I have...

Every time you replace the fuse you do at least $50 more damage. With both output modules removed, bring it up with a 60 watt bulb or so and a 5 amp fuse. If successful discharge the caps and install one module and bring it up on a 100 watt bulb. If the bulb doesn't dim then switch to the...

I have the drop-in relay board. Also have a few of the power switches. Highly recommend my triac power switching board to avoid switch failure.

Jump on it. URIE is high quality pro gear. If you don’t like it, I’ll buy it.

An oscilloscope is of use only if you have a decent oscillator. The HP 204 is cheap, plentiful, and relatively low distortion. Digital scopes have their advantages that can be good if you need to capture waveforms. I bought a Rigol 4 channel scope with all of the bells and whistles and sent...

A cheap load bank can be made with hot water tank heaters. Home depot has a 240 volt version that is very close to 8 ohms. Downside is they have to be submerged in water or they burn up immediately. A 5 gallon bucket with a metal lid works well.

The 4000 is a disaster waiting to happen. It was designed before double sided boards with plated holes were available. It has a mother board with male connector pins and daughter boards that plug in. The pins on the motherboard have cracked solder joints. If a 4000 is going to be used it...

Transistor failure modes are open and shorted. Any meter with a diode function will meet this requirement. This includes $10 versions at Harbor Freight. I've tested 1000's of diodes and transistors this way. More advanced devices have a display and list NPN or PNP, type of device and current...

Well, you've certainly been busy. A few thoughts: I'm not sure what the quality of the pots are, but it is a minor concern for reliability with them mounted directly to the board. Of course, plated through holes help. I think very few people will want to buy the equipment to work with surface...

Sometimes you do things, not because you have to, but because you can. As I'm now retired I can take the time to mark up the schematic with Joe's comments. See attached. I think I know opamp theory reasonably well, but the tone control schematic gives me a headache. Joe, can you explain...

I’ve got a pile of the original jacks for the 200. Bought them last year when a surplus place was closing up shop. If you want exact original replacements, let me know I just looked at the jacks I bought. Apparently, I didn’t understand their function. With nothing plugged in to the jack, the...

I didn't get very far and abandoned it.

I'm not sure that shorting type is such a god idea. The 2000 I tried was noisey and I wondered if the shorting current in the ground traces from the shorting jacks contributed to that.