Various tech chores mentioned before.
Hafler P500 - Right channel intermittently cutting out after several hours of use.After probing around, I could cause a failure by wiggling the Mono/Stereo switch.
I decided to hard wire it to stereo mode since that's the only application we'll use it for (clearly labeled now). The contacts of the open frame switch were blackened with oxidization. I exercised a bunch of connections and cleaned out some of the grime while in there.Working properly after a few days of abuse.

Altec 436 (both) -Different problems with each compressor, not related to tubes. These were modified in the 90s by someone to add attack, and release time adjustments, and an output attenuator. On both, there were old carbon power resistors meausring 1/2 their marked value in the power supply (R14).In general, neither is behaving predictably or properly.Rebuilding both. One to a popular mod (NY Dave's design), the other to a EMI RS124. I'll let you know if they work years from now.

Fender Deluxe (modified 5C3 using a 12ax7 and 12ay7) -Motorboating oscillation when the "mic" volume was all the way down, guitar connected to the "instrument" input (like normal). Motorboating would stop when I turned the "mic" input gain up a little. After probing around a bit, looking for clues, finding red herrings I discovered there was a 12AX7 where a 12AY7 was supposed to be (preamp tube). The amp was modified/rebuilt a long time before we got it through a friend. The work looks solid, and kind of a hybrid of 5C3 and later designs. It also has an adjustable pot on the voltage divider where the lower half of the phase inverter gets its signal. I presume this trims the level for that polarity?

Soundfield Mk IV -When the stereo outputs of the control box are connected to the Neotek Series II line inputs or insert returns (unbalanced inputs), there is a hum. This is not the case when terminated to the balanced inputs of the Pro Tools rig or tape machines. This noise is present whether or not the mic is connected, and even with the unit off, power cable unplugged. A couple of notes:The outputs of the Soundfield control box are 'impedance balanced', so there should be no problem driving unbalanced inputs. The way this is set up is the control box lives in the control room and connects to a dedicated Soundfield 12-pin socket mounted on the mic panel in the live room, via an 8-pair snake (mic cable extension). While listening to the hum (no mic connected), I disconnected the mic cable extension from the cont. box, and the hum went away. I then touched the shell of the connector to the cont. box chassis and the hum returned. Looking inside the connector, the shield-drain wire for the snake (surrounds all insulated pairs) was terminated to the shell. When I lifted it, and plugged the connector in, the hum was absent again. I suspect and will confirm later that the other end of this drain wire was similarly attached to the female panel mounted shell on the mic panel. Any noise or potential on that mic panel box + conduit could have a path back to this cont. box, and be heard for the following reasons...Looking at the control box schematic, I saw that the safety ground for the IEC power connector was terminated to the main pcb, then sent through a 10 Ω resistor to the pcb's point of contact with the chassis. As far as I know, this is a big no-no. Simply having the safety ground travel through the pcb to the chassis is a problem on its own, much less through a resistor. What would be the utility of this? The signal ground is also tied to the chassis via another 10 Ω resistor in parallel with a 100nF cap somewhere else on the main pcb. Since the chassis could have noise current, via a ground loop (from the mic panel box/conduit other equipment 100s of feet away), antenna action (with the relatively long path to earth), or some other source, it could infest the signal ground? That noise would be transmitted common-mode when the outputs are terminated to a balanced load, so that might explain the silence there. I have to admit I'm a bit turned around at the moment, and will look at it again later.For now, I'm isolating the mic panel from the control box, eventually having the snake to it just be an extension of the mic cable electrically, with only one reference point for earth, the control box. The power safety ground is now attached to the chassis directly. Things are quiet.

Neotek Elite-Aux Master module faceplate flexing too much. Busted stud on the back of the faceplate. Popped the pressed stud stump out, and replaced it with a new screw. Cleaned some connections while I was in there (related to the Cue source selection).Other bits and nagging level tweaks to do to that module

Urei 1176LN (version H modified by Alactronics)-Giant pops and noise when pluging anything into it.Found 10-12 vdc on the input (XLR pins 2 and 3)! This 1176 uses the op amp differential input design working off a single 30v supply (amp inputs resting at 15v). The inputs to the amp are coupled via dc blocking capacitors with the connector side floating. One of the electrolytic coupling caps (film in parallel) was bulging and fell apart while I was removing it. I suspect they were leaking dc quite a bit. Replaced the electrolytic caps and added two drain resistors on the connector side (100kΩ) to keep things at 0 volts. -Elsewhere-Counterfeit Lomo 19a18 -Intermittently working.Cold solderjoint on the cable mic connector for the ground/shield conductors. The wires were loosely held in place by an insulator tube around the pin's solder cup. Checked all PSU voltages, replaced missing screws...

Testing on the Elite,Making a new wire loom for the Neotek Series II power supply (moving it out of the control room soon).

Modding an Altec 436 to the EMI 124 idea.Later :Finished with the first one. Going to test it in action during a mix session this week. The "recovery" time options are slow, but not as bad as the original Altec. I might have to replace some noisy parts, but I just want the concept to be proved before burning more time on it.

Sennheiser MKH-405We had this mic sitting around for a bit. Installed a little phantom to T12 converter inside a 3-pin din connector to XLR umbilical so we can use it without an external supply.

Neotek Series II-Mute leds on unmuted tracks flickering cyclicly causing quiet "tick-tick-tick" noises on the 2-mix bus.This could be stopped by turning off the Mute Group/Solo logic feature (mod). I narrowed it down to channel 26's Mute Group/Solo isolate function switch (there's one on every channel). When I set it to the equivalent of "solo defeat" (not muting when other channels solo), all was good. Pulling the channel out, I saw that a diode was barely touching the leg of the mute relay transistor (both mounted on the switch itself). I simply separated them and tested the channel. Works now, but the problem went away before, then came back after a day or two. I don't know why this problem just now showed up, other than maybe it was warmer in there at some point and things expanded? The room is pretty well climate controlled, and mostly cold. I'll go with ghost.

AB International Model 600LX Power Amp-
No or really low output.

This was being used for the coffee table set of speakers in St A's control room.The ±15 power rails were being loaded to less than 1 volt. These power rails supply the input op amp, and discrete input section of the power amp. They are derived from the ±80 volt unregulated DC rails by a simple zener clamp regulator circuit (no pass transistor). Using the bench supply to power that ±15v path, I could see a large draw of current, which I isolated to the input board. This board had only one dual amp (4558), which was f'ed. I replaced it then tested things out. Incidentally, the cooling fan (brushless 12v DC) was frozen. I disassembled, cleaned and lubricated it. Now it's as good as new(?). Never did that before.