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I installed the relay board in Jim's 400II. He got it home and the relay wouldn't engage. He brought it back and I tested every part in the channel. All were good. That left only the opamp as a culprit. Direct couple amps like this do not allow for signal tracing to troubleshoot. Pulled...

The likely reason R23 burned is Q10 has shorted. Did you use the light bulb test set in the relay board instructions? It's intent is to avoid this type of problem. Start by checking every P/N junction on the board using the diode scale. Compare the two channels. See the troubleshooting...

The date codes on the electrolytics are late 70's. The chips appear to be early 80's. Sounds about right as the PCB is single sided without plated holes. Most everybody went to double sided boards by early 80's. Plated holes reduces cracked solder joints.

Does Perry have an affection for rainbows?

If you wish to send a Phase Linear amplifier into orbit, connect each output to an oscilloscope with a grounded power cable and a grounded signal generator. The amplifier will make all kinds of oscillations and squeals as it tries to self destruct.

I saw a pair of trashed 4311's for something like $75 at the San Diego flea market a few years ago. Everything was there, cabinets were a mess.

I had a set of 1A's I got through AudioMart around 1979. Had them on college campus with a P/L 400. Roasted a few diaphragms. Sold them and bought JBL4311's which held up better to abuse. About 15 years ago found a pair of 1A's at a thrift store for less than $50. Diaphragms OK. Woofers...

I ended up using warm white LEDs and they came out pretty good. The lights for AM FM indicators are the same as the bipins Used in the phase linear light boards. I had the bulbs I needed except for the dial indicator. Used a LED, a 1N4004 diode and 470 ohm resistor. It fit perfect and did a...

I picked up a Marantz 105 tuner recently. It needs all new lamps. What's the best way to access them? Remove the front panel? Go inside?

The warm white was my original intent. I also have a Marantz tuner to do and bought the blue ones for that. The person I’m doing this for also registered the same comment, warm white it is.

I'm working on an early 400 that has the fuse style incandescent lamps. I bought blue and warm white fuse style LEDs. The light winding on the transformer is only 6.7 VAC with a line voltage at 120 and the 8 volt LEDs were dim. I considered adding a few turns to the light winding on the...

Speakers connected to an amp without an output relay have a "thump" a few seconds after turning power off. That is the result of the DC caps discharging to the point the front end transistors can no longer maintain a proper DC offset. As I recall the positive DC cap discharges faster than the...

Any changes to the opamps should be met with an oscilloscope and low distortion oscillator, or better yet, a distortion analyzer to check stability. At a minimum decoupling caps on the power supplies (at the chip) should be installed. That's not an easy task. Consider installing sockets to...

Oil filled caps are AC only and much smaller uf. As I look at the assembly, the caps vent into the board and there is no hole for venting. So the debris was forced down to the chassis. That means there is electrolyte on the chassis. You need to make sure there is none in the transformer.

The white film cap is 7138, 38th week of 1971. Those values are common snubber caps today.

Cabbage Cases is about 20 minutes away form me. I can inspect/approve the prototype before shipping as needed.

When I worked at the pro sound shop, one of the mods for 400's included an extra long bolt on the bottom transformer hole. There was a bracket in the rack that the bolt slid into to support the transformer weight.

I've posted the attached pdf before, but it's worth putting up again. Those look like oil filled caps, not electroytic. If an electrolytic cap vented I would expect a pin hole. Worst case is catastrophic rupture with a lot of confetti.

I noticed on the relay board that R6 and C3 are not populated. This snubber protects the chip from the inductive kick of the relay coil. The values are .1uf and 100 ohm. The alternative is a clamp diode (1N4004) across the coil on the back side of the board with the cathode on pin 8. The...