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Wow, from the photos, the main DC caps are a few months short of 50 years old. The driver board appears to be a prototype. Good for nostalgia. Not necessarily good for long term reliability.

Clarification, C111 is the critical cap for low end response. However all electrolytics should be replaced. The display boards have a pile of electrolytics too.

I've seen R101 (7.5K/2W) fail (open) several times. When that happens it shows no sign of heat stress. That channel goes full DC on the output. If one or both channels lacks low end, C101 (100uf/6.3V) has drifted.

Service manual attached. Don't be afraid to read it cover to cover.

If the bias gets much higher (600 mv), all outputs will turn full on and go to war with each other with mass casualties. Once the bias is reset, wave a hair dryer from a foot away or so, on low heat, at the bottom of the heat sinks while watching the bias. Bias should decrease slightly as...

Didn't build any. I rember reading some articles. Was it supposed to be a low TIM dessign? I think it was in Audio or Audio Amateur. I probably still have the articles.

I've got 2 Dranetz 626 power line monitors that I'm tired of looking at. They're available to whoever wants them for the cost of shipping. They're about 25 years old. Worked the last time I turned them on which was about a year ago. You set up some parameters and they spit out numbers if the...

here is a link to a great paper on snubbers and quencharcs. Paktron quencharcs

At my day job, we used 7700uf caps by the train load. They tended to run close to 10,000uf. Then 15,400 became available in the same can. We started doing capacitor change outs 1 x15,400 for 2 x 7,700 and found out the 15,400's were on the low side of the spec and we didn't have enough...

Whatever you do, do not read this page from the service manual.

I really like this one. With only 50 watts input power it puts out 1KW with a max power of 2KW. It sets a world record for efficiency and does it in a package about half the size of a 400 transformer. With this technological advancement, perpetual motion is certainly around the corner.

Does it matter that the one in the link doesn't ship to the U.S?

I''ve seen so many 400's that came out of rock-n-roll racks with butchered faceplates. The weekend warrior typically used a hacksaw or 3/8" drilll bit. The 200II front panel is 5 1/2" tall which makes it difficult to shoehorn into a 3 space (5-1/4") space. The photo shows the offset ona 400.

Adaptor cables. Phone may not have high enough output voltage Lightning-1/8" 1/8" to RCA

Sorry to rain on the parade, but, leaving the amp on doessn't solve the problem. It's a band aid. As mentioned the front end transistors are failing. I've seen this over and over again. The question is not "if". It's "when".

A science fair project requires at least 5 meters/instruments. This is certainly a fine one. Stacked Keithley's double as a stand for parts trays.

So Steve Mantz is still around? I spoke to him about 10 years ago. I have a schematic, from 2009, of a mod he did to eliminate the boot strap circuit by adding a transistor between the collector of the bias transistor and V+. He kept the discreet front end circuit. He also added what he...

First of all, hats off to JTAT for doing some research. Apparently the decision to install the relay board saved a speaker or two from lots of DC. I haven't seen a PL14/20 board in the last 5 years that did not have one or more front end transistors (Q1-4) that have failed. Quite common is...

I'm going to be hard pressed to believe that turning on a bunch of amps will sag the line voltage enough to cause a gen set to start. I'd expect breakers in the panel to trip first.

I just finished up a 400 with all of the goodies. Getting the transformer isolated was a challenge. I first tried heat shrink, which, to no surprise was too thick. I considered #12 screws and metric alternatives. While staring at the wall it hit me. Packing tape! The standard packing tape...