I drove a couple towns over and picked up a Gates Studioette M-5381 yesterday. Let's have a look.

Solid logo, I haven't yet put a fine point on internal date codes, but the manual was printed in 1962.

Only 24 inches wide, seated in my work chair. I'm going to have to make a better place for it & will follow up with a better front panel shot later.

Recessed VU meter, quite modernized styling over the RCA BC-3C from the same era.

The front panel of this unit has escaped the rough hand of modification. There are some additional holes on the sides, but for once the face is left alone (which reminds me, I really need to post pictures of the basket case RCA).

This is where the serial would go these days, curious if there are identifying marks inside that would point to record with the manufacturer (not that it would do me any good).

GUTS. Hinged front is the control surface. Moving into the chassis, lower left is a pair of microphone preamplifiers, each with input and output transformer (albeit somewhat puny ones for the era, no need for 5 hz on AM radio, thanks) and room for one more. Shifting right we see a solitary UTC A-21 doing duty on line level inputs, keeping those voltage regulation tubes company. Continuing on to the right there is the program amplifier with three pentodes and a dual triode, the circular transformer being input and the larger rectangular transformer being output.

Shifting to the back row, at far left there is the monitor booster amplifier, 150 ohm balanced line input to 12AX7 pushing... a push pull 6BQ5 monitor amplifier which wisely has its output iron bolted to something more substantial than phenolic PC board, and on to the power supply.

Here's a closer look at the power supply, nothing unusual: mains transformer, rectifier tube, a couple of chokes. The output transformer for the amplifier stage is in close proximity, which will confine power hungry pulls on the B+ well away from high gain stages. Those two relays will probably go unused. I haven't seen a power switch on this unit yet, I will certainly be paying this section some scrutiny when update time rolls around.

Staring too long at this may make me delay diving right in. No! That's the wrong angle, this looks like meditative fun to sort and resort. Wind and dive.

Conductive plastic or mechanical fortitude? I know which direction my preferences lie.

I found the maker's mark in the Daven cap interesting enough to photograph, given the amount of scuffing (original as far as I can tell).

Apparently the #3 gap is standard from factory, designed in room for expansion. Who knows what will take place there in the future? Since I have the manual, and having roughly 52 hours notice of collecting this device spent some time fruitlessly searching for a digital copy (of which I could find none) I intend on scanning up a pdf and sharing that with the digital universe once I get a chance.

Here's a closer look at the preamps.

A truncated shot of the program amplifier (I think I'd term this summing section, but since it was named from the factory I'll show it a little respect). Observe the dirt build up from the right end..

Closer look at the monitor booster.

Yes, some clean up is in order.

...

The fan was added post factory, it would have been a good idea to put a filter on it. After seeing this I'm pretty sure the fan is getting the heave, I plan on undervolting the mains a couple percent, which should rein in the heat a bit. Honestly, having looked at the underside of the lid I don't think excess heat was ever really an issue.

Exposed tabs! SO much nicer than having to work through a punch hole in the chassis, this one's a keeper for sure.

I was recapping my Roland SMX-880 a while back and got hung up on the fact that I hadn't observed the fact that the 10uf electrolytic at input jack was a bipolar. Quick test confirmed that this cap is situated in line with the signal, it is the first thing the signal hits.

I wasn't about to put some polarized cap there, so the unit was set aside to await a parts order. In the meantime I read a bit of opinion on the internet I found agreeable: "The best sounding capacitor is a piece of wire".

Brilliant. Upper right corner, I hadn't any plans to subject it to DC anyway.

Where was I? Oh yes, I had polished the legs of all analog ICs in channel 8, reinstalled them, and then observed function. Success!

So naturally at this point I disinter all the patina laden ICs in channels 5 through 7, clean them up, reseat chips, reinstall channel cards and apply power.

Nothing. Well, unless you count the full meter deflection of 5-8; audio certainly isn't passing through any of these.

That includes channel 8, of course, which, by my own observation was just passing the first tier of functional test and literally has not been touched since.

Pull card 5 (again, if I was thinking clearly and weighing out all the evidence this step would have been reduced to one selection, but I was at this point a touch flustered). Power up, 6-8 pulse the VU. Power down.

Leave 5 out, pull 6 & power up; 7 & 8 pulse the VU, power down.

Pull 7 & power up, channel 8 shows a minor bump on the VU and now passes sound. Power down, reinstall 5.

Power up, channel 5 shows a minor bump on the VU whereas channel 8 does not deflect at all, both channels pass audio. Power down and install 6, which completes the pattern as expected.

Channel 7 contains a problem that was pulling down channels 5-8. Having my quarry fixed, I now begin to puzzle this out logically, and based on the power rail observation made previous I begin with measuring the rails for shorts. -15 volts to common measures 0.8 ohms.

Ah, the dogs, they have your scent. All integrated circuits are pulled, the short remains. Of course it wasn't going to be that easy. I pore over the schematic for all points tying directly to the negative rail, and choosing for now to ignore resistors narrow my focus to a dozen or so parts and begin to pull them out, one at a time to determine which part is failed.

Next time, I'm going to start with the caps. The dense two sided PCB has made me out for a bungling idiot, and before I actually pull any traces that are important (this was just an insert) I shift my method to cutting.

Which, while destructive, limits the destruction to parts at hand. I'm still exacting far more destruction than I feel I should on this simple task. This particular component was just fine before I came along, WOOF.

Having ruled out transistors I then focus on capacitors. C4 here is the problem, a Matsushita 1 uf @ 35 volts, it's marked as being polarized. Tantalum? Odd package, I can get those values in a similar dimension in ceramic, which is my plan.

Of course, I threaded up a reel of tape and learned my record levels have been killed (previously 3 & 4 had recorded well), now everything reads high to tape and plays back low, with the exception of previously recorded material. So now I chase a common point in all channel recording. I'm thinking bias as a starting point, have mercy.

Having temporarily ruled out a logic problem (which seems logical in retrospect, since I have observed the status LEDs appear to be driven from the state of the channel card itself and not the logic commanding the card), it was back to troubleshooting the machine as a complete unit.

While I had all the cards pulled I naturally brushed out cobwebs and hit the edge connectors with contact cleaner, so it was only logical to fully reassemble the unit and see if a good cleaning did the trick. No change.

Next step was to narrow down point of focus. For brevity sake I'm just going to observe the behaviour of the VU meter on power up and power down, since in consulting a friend who has a very functional version of the same machine I was informed that meter deflection of any sort in response to the on/off switch was unusual. So I swapped cards 4 & 5.

No change in 5-8 deflection at power up, though now #4 was pegging the channel 5 meter as a steady state while the natives along 6-8 returned to zero. Quickly power down & confirm card was seated correctly. I pull channel 4 card & channel 6 card to compare, they are, for all intents & purposes identical (beyond the fact that they carry factory stickers indicating their home channel).

I then install the channel 4 card into channel 6 slot, placing channel 6 card into channel 5 slot. 5-8 full deflection tap and now channel 6 is pegged. Power down.

While channels 1-4 have not been considered suspect, due to them actually functioning (and bolstered by the fact that channel 4 has in fact recorded to tape and passed the listening test, which I would like to think is pretty stringent). I then swap Channel 3 with #4 in 6. 5-8 full deflection tap and channel 6 remains pegged. Power down.

At this point I overlook a step that could have saved me a little time and effort. It should be obvious that I am not a factory trained technician, nor am I intimately familiar with the workings of this machine (getting there). I'm pretty much working in the dark with my empirical approach and a set of freely downloaded schematics.

Make no mistake, I am brimming over with a sense of gratitude toward the good people at AnalogRules.com, for without these highly useful documents I would quite simply be fucked. However, there came a point at which deep circuit analysis turned into a hide and seek sort of affair due to a lack of clarity in the scan. So yeah, I'm pretty much just making this process up as I go along.

So, my next step was to remove all the cards, set 1-4 aside as known functional and install 5-8 into the 1-4 slots. Anyone care to guess what happened?

Nothing, unless you count 1-4 meters deflecting fully on power up. I run signal test to confirm a complete lack of function.

Based on this observation (and brownie points to whoever catches my mistakes here) I shift focus on channel cards 5-8 themselves, and ignore for the moment the steady pegging of the low number cards in high number slots (another hint). I had deemed the probability of discrete failures on the four cards, right next to each other, as highly unlikely, but it's worth a look anyway.

All my analog ICs are looking a touched charred (this batch is among the cleaner looking). Granted, there's patina on the analog ICs in channel 1-4 too, but I'm not paying them much scrutiny, as they are not problematic. Incidentally, all the digital ICs are looking quite fresh & nickel plated, so it's a metallurgy thing, perhaps there's a high content of silver in the legs. Whatever.

So, channel 8 is my guinea pig, I've plucked the chips and go to work.

600 grit sandpaper and a little time, before and after shot here.

The ICs cleaned up pretty well, flushed the sockets with contact cleaner, reseated the ICs into channel 8 card and sink that channel into channel 8 slot - with no other cards with the exception of the logic control. Power the machine up. Minor deflection on channel 8. The card passes sound!

It is at this point that, flushed with a sense of progress and ready for a break I happily report to my magnificent and wonderfully patient wife that I've finally secured what appears to be a solid lead amidst a convoluted mess of red herrings. HAHAHAHA, oh the humanity.

So back to the Otari MX-5050 mkIII 8. Symptoms as follows:
On power up meters 5-8 deflect fully then return to zero.
On power down meters 1-4 deflect fully then return to zero.
Setting monitor to all input, audio passes through channels 1-4 while 5-8 has nothing.

So, my thinking is naturally focused on the split point between channels 4 & 5. With that in mind, and based on the observation that a lot of the CMOS gates used in logic direction are four per IC I started my analysis there.

As you can plainly see, that angle was not fruitful. There is not a single instance of component pairs straddling the 1-4/5-8 configuration. With that, I cracked the case and began to pull cards.

Here's the control card to go along with the (partial) schematic above. The fact of the matter is that this card does not have the same part number as the schematic I've been working from. I settle into the idea that I may have to resort to a trace by trace comparison to see if I can narrow down a culprit IC, but since I'm pulling cards now I may as well go for broke and thoroughly give everything a visual inspection.

So far all the cards & traces look good. I know, that just rules out the obvious...

...having been bit in the ass by the obvious after chasing the esoteric a few times too many that's where I like to begin.

While I have the motherboard exposed like this I do a continuity check on my pin 2/3 swap on the inputs and outputs of both channels. Everything measures up well.

Without really getting into photography it's difficult to demonstrate the look of backlit traces. Let's just say that evidence of pulls, shears or cracks do not exist. Everything passes on the visual level. One thing I do notice, is that the +/-15 volt supply rails (brightened in the picture) just span 1-4 and 5-8 (with a contiguous ground reference). This is the first point of a well defined 1-4 versus 5-8 I have observed on this machine, and it may prove useful later. But for now I simply apply power and confirm that the supply rails are delivering at all locations.

Next up, chasing a series of red herrings..

Okay, I've known about the Otari XLR pin 3 hot configuration for quite some time now, but in practice I'd never run into a catastrophic failure because of it (that is to say, I was able to record and playback audio on the 2 track machine with little issue). Therefore, that bit of information sunk into the dusty corners of my mind where it was wholly ignored. Of course, all that free riding came to a screeching halt once the Autogram AC-8 was planted in the audio control trunk. See, in my wiring up the output I included unbalanced 1/4" phone plugs which were at one point normalled to the monitor amplifier.

So, when I connected the pin 3 hot, pin 2 ground configuration of the Otari to the pin 2 hot pin 3 neutral (actually earth referenced thanks to my inclusion of unbalanced 1/4") configuration of the mixer output, a whole lot of nothing happened. Nothing to the tune of even killing the monitor feed to the amplifier.

I had entered into really easy diagnostics, unplug cable = sound, plug it in = zilch. So, with a nod to the widely published pin 2/3 issue, I built a pair of XLR cables with pins 2 & 3 swapped. Solved. Of course, at this point I recall a few months previous while I am working on the basket case MX5050-8 and can't get any channel response out of it, which, at that point was a step backward but given the hard life the machine has had I place it closer to the parts bin. Why yes, I had been feeding it audio from the Autogram while failing to get signal, it was just prior to the monitor amp feed modification.

So, the 2/3 swap XLR cables worked here too. I was able to commit signal to tape and playback (on conventional XLR), and it sounded good. So, my options now are to make another 6 pin swap XLR cables, or just modify the machine to reflect pin 2 hot. Ready to cut traces and jumper stuff at board level, I was met with this magnificent sight. Build six special purpose cables, or simply rewire 16 connectors?

Easy decision.

I did this, from poor placement in a room (that gets gear hauled in and out of)...

..and this. Very preliminary internet searches do not favor the notion that this is an easy & standard current production off the shelf part. Since the switch still works I think I may drill a small pilot hole in the lever portion and turn down a bit of small bar stock to have an end pin, then epoxy the new arm in place. Worse case I'll still have to find a replacement switch.

Since this machine got hammered the interior finds include stuff like this, from the side panels.

Took in the new Baktun with some long overdue recording yesterday.

I'm still not clear of the underbrush in regards to the Otari, but it performed very well on tracks 3 & 4 yesterday, proving that continued hammering is warranted. But, this post is not about the tape machine.. in setting up to record I decided to utilize the long neglected Eventide H3000. I discovered forthwith the fact that the soft keys had entered into the realm of unresponsiveness, robbing me of the ability to edit patches and really use the instrument.

That simply would not do. Guts up.

I have some number of gaps in memory, as in the manual references patch programs at certain numbers that for all intents are inaccessible on this machine. Seeing as how I can still construct whatever I want, I'm ignoring that right now. The H3000 sounds good, and is a capable effector (honestly, if the digital vs analog sound quality debate comes up I'll point to this thing as the STFU card, and I am of analog bias). Anyway, I'm not here to talk about the selective memory either.

I just find it interesting that ROM doesn't fit the socket, and am curious about the empty socket to the right. No matter...

When I bought this it was inoperable. It would power up briefly, then the relays would click into bypass and everything dimmed out. The cause of this was the plug depicted here. Addressing conductivity at this connector brought the unit back to life. So yeah, I'm always on the lookout for rack mount Eventide gear that exhibits those symptoms, even though I just gave away the thousand dollar fix.

Anyway, back to the soft keys. Pull the bottom cover and this is the access. Spray liberally with residue free contact cleaner while tapping the switch. Allow complete evaporation, reassemble & enjoy your fully responsive instrument!

I've been fine tuning the Autogram AC-8, I had pulled the MXA-1 & LA-1 modules from the AC-6, as there was pronounced imbalance between the right & left sides of the audio feed. A little bit of swapping sorted this out. Mind you, this tuning had occurred while the studio monitoring system was piggybacked on the program output feed.

Such a configuration is less than ideal for a few reasons, being able to monitor the audition channel for one. Having access to a control room volume other than amplifier input trim or mix levels is pretty handy as well.

The problem was that while input/output feeds all terminate to barrier strips for easy interfacing with the rest of world, the monitor feed of the AC-8 was internally routed to onboard amplifier sections, so the original monitor connections are post amplifier speaker feeds. While I have few reservations on the standard of quality that Autogram put forth into this unit, I've already got a monitoring set up slated for use and have no interest whatsoever in using the MA-1 monitor amplifier between my ears and the work.

Fortunately the monitor modules are built on standard eight pin Amphenol as opposed to the nine pin variety that is used for input modules. I built a pair of cables to tap into the signal input of the amplifier connector and route that into my monitoring system.

Suddenly, able to A-B the theoretically identical program and audition channels against one another, it became very apparent that the AC-8 was overdue for a recap.

I had procured some new production axial capacitors a short time back to recap some modules. However, while I ordered them based on the physical package of the original parts (while upscaling voltage values as the existing components didn't allow for a healthy safety margin) I was greeted with the fact that the 100 uf were larger than advertised. This had delayed installation until my ears notified me that we'd passed from preventative maintenance into degraded quality damage control. In the above image, the MXA-1 module at right has the new caps versus original equipment at left.

In the above image, the LA-1 module at left has the new caps versus original equipment at right... and so on. If you scrutinize the upper left hand nut of the right hand unit you'll observe a mysterious residue that greeted me in one batch of modules.

In earlier attempts to balance out the stereo field I had plucked all the MXA-1 (mixer summing amplifier) and LA-1 (signal output line amplifier) from the AC-6, which has evidently had a much easier life than the AC-8 (based on comparison of interior module conditions). The LA-1 pictured above is from the AC-8, I know this because the AC-8 has an additional mono summing channel, resulting in five of each module type whereas the AC-6 does not. All five of the LA-1 modules are similar in condition (the MXA just have more signs of heat).

While the theory could be advanced that the big sound from this desk comes in part from the hairy legs of the savagely unfettered sasquatch looking transistors, I did my best to knock this stuff back a bit.

The audiophile skin effect theorists could have a field day with this.

After over a year of riding around in a box the Ramsa WR8210 was put back together.

Evidently I've some slider caps to hunt out yet.

Living in a box didn't do the mixer a whole lot of good, as evidenced by the bent PCB for channel seven. The wear & tear is limited to aesthetics, and thankfully that's invisible once everything is buttoned up.

I either forgot to count up the caps in the headphone amplifier circuit, or they've been misplaced. Since this is a less than critical point I ignored it (along with a couple in the LED bar graph driver circuit) so I could reassemble the mixer and move on to the next thing.

At some point in the future I'll wrap up another year + old project!

Dusting off the PA since it's going to see some use this fall, and I'd really like to dodge the last minute cram if at all possible.

While I was tooling about that corner of the garage I figured I'd give the pile of dead speakers a more thorough examination so I can start chewing on my plan for them as well. Enter a Cerwin Vega 154FM that was beaten into submission at Eugene Noise Fest 2007. If I had to wager a guess, I would say it was during The Sunken.

Which led me to this observation. Furthermore, clamping a battery lead onto that little sliver of wire confirmed that everything else was intact and functioned as normal.

Upon removal of the dustcap, which is a two layer fabric mesh over aluminum assembly, I was greeted with less than optimal news. Judging from the concentric creases, it would appear as if the tinsel fell out to prevent the voice coil from punching through the cone.

The eyelets that tie the tinsel to the voice coil wires are on the verge of punching through as well, observe the discoloration of the VC lead terminating into the empty eyelet, that'll be explained in a moment.

Due to the weakened cone structure, the voice coil assembly and immediate surrounding area could close up to the aluminum dustcap when the speaker was in it's positive excursion. This effectively shorted the output of the amplifier across the dustcap, producing the spalling seen here and heating the joint up enough to cause the solder to flow, whereupon that connection acted as a fuse and opened up eliminating further damage.

Repairing the electrical connection was easy. Reinforcing the integrity of the cone to avoid repeating the failure, however, resulted in the plastic surgery disaster seen here.

I'm not ashamed of this, it is ugly and I would not endeavour to recreate this, but honestly this driver has been sitting around awaiting a recone for 5 years, and if this botch-work quilt of a fix extends the use of an otherwise trashed object, I'm all for it. I realize that with the pooled glue splints the delicate nuances of whispering sweet lower mids have been pounded into the bog, but since this is a piston being deployed in the 40 to 100 hertz range that wouldn't have come up anyway.

I replaced the obviously failed capacitor that I spoke of in this previous post, added a 2 amp fuse which had gone missing at some point in the annals of history, and then applied power to the Kloss VideoBeam 3000.

Delightful!

The closed door was the nearest thing I had to a flat white surface handy, clearly the positioning is out of whack. Given the results here, I'm not overly concerned with proper installation, as I do like the deep explosion of colors reaped through placement outside the range of focus and alignment.

Reminds me of the Martians in the 1953 version of The War of the Worlds, a fine collection of stills to be found here: http://www.cloudster.com/Sets&Vehicles/WarOfTheWorlds/MartianWarMachineSht3.htm

Building a rotating cradle to allow on point unrestricted tilting of my video camera for deployment in video feedback.

This is the build up to this point, camera is mounted within an aluminium drum riding on rollers. I understand the drum is an out of spec helicopter part that I salvaged from a scrap bin, the rollers are from an old color photograph processing machine with One Drop yo-yo parts elevating the drum (and all the non-round elements) clear of interference.

I should have taken a picture of this prior to modification, it'll have to wait until I grab another one (I believe there are three of these: developer, stop & fix) to photograph.

My initial visualization of the mounting of the camera was a lot more elaborate than this, which amounts to a 1/4" 20 tpi screw through a shaped woodblock into the tripod mount of the camera. I've still got to remove some material from the woodblock as it places the camera just a touch high of center.

This was a problem at first. I had initially been designing around the solid roller support depicted in the baseplate picture above. My plan was to countersink the hardware into the sidewall of the drum, but while the drum is indeed quite thick (roughly 1/4") there would not be nearly enough material remaining to carry the weight of the camera.

Furthermore, each solid roller rode on a couple rubber rollers that tilted outward due to limiting myself to precast positions in the plastic end plates (that is to say, the outermost roller is lower than the inner). This resulted in the solid roller wanting to walk off the supports when the drum was rotating toward it.

I installed the shrouds on each side to eliminate the walk off problem, but the solid rollers would still shift, which resulted in the entire assembly moving off center as well running contrary to the entire point of building a centered rotating mount in the first place.

So I had a two tier puzzle that needed resolving: A) I needed a gap that will allow the button head of the hardware to pass the rollers without being a disruptive speed bump, and B) I needed a simple and unrestrictive method to fix the larger bearing rollers in place.

Both puzzles were solved by ousting the heavy solid bar, and wiring up One Drop yo-yos to the structural bar below the rollers.

Plenty of gap to allow that screw head to pass.

I still need to reduce the size of the wooden shim, but it's close enough to center to work as is at a live video show this coming Friday. Extended plan includes motorizing the drum and incorporating CV response to the motor driver.