Otari MX5050 BIII-2 Adventures

SCompRacer

Got another one that needs some TLC. Otari MX5050 BIII-2. Born in 1995. It's a highly regarded commercial grade deck with significant upgrades over the previous BII. This one is a two track. 4 track playback was an option when purchased, but this one doesn't have it. (For $700-$900 I could add it with a good condition BII head block). 3.75, 7.5 and 15ips speeds. Switchable NAB/IEC EQ. More info about it later.

It was stored in a damp environment. We got some warm days here, 70 today, so I took advantage and did some refinishing. The rack mounts had some rust and corrosion. My phone was charging so I only have two pics from when the deck arrived last February. The flip up aluminum head cover also had some corrosion.

I found a decent paint match at Home Depot for the head cover, Behr Metallic Oil Rubbed Bronze. I purchased some Rustoleum Textured Black for the rack mounts but no joy, wouldn't spray. I didn't want to go back to Home Depot today so I used the bronze paint. First, I sprayed some Rustoleum Rust Reformer on the pitted areas of rack mount after sanding and wire brushing.

I cleaned the front up and will eventually start on servicing it.

mhardy6647

Godspeed, @SCompRacer! Looking great so far.
I like Otaris. They were tools -- not (typically) in the rarefied upper end of the audio ecosystem, but down in the trenches. Little radio stations, e.g. And they just slog(ged) along and did their jobs.

SCompRacer

It is very well built and heavy. Boards swing out for easy service. One of the improvements over the BII, the BIII uses standard NAB hub adapters. It was in bagged isolation for near 9 months. There were some ugly spiders seen in the vents upon arrival. The PA spiders looked badder than my basement spiders. Upon reviewing pics I spotted another one above and between the heads.

I removed capstan motor to service the pinch roller and tape lifter linkage. The lifters were sticking. All Nichicon caps including some Gold.

"The Otari BIII upgrades over the BII primarily in the tape transport, which features a smarter, logic-based control system for smoother and quieter tape handling, and includes soft-touch buttons instead of the BII's electromechanical ones. Other improvements include a Parallel I/O interface, locking spindles, and improved NAB large reel clamps."








Balanced in and out.

mhardy6647

Yeah, the adaptors from the BII are a pain. I have four of 'em (maybe six... I forget) and all have some issues but they will work (even with the deck upright).

Typical pointless, egocentric aside follows:
I should've kept one of the two carts that came with the three I acquired from a local radio station... but I knew a couple of guys who had more legitimate uses for the carts than did I, so I suppressed my only child greediness and gave 'em away (with the decks that were on them).

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mhardy6647

Yeah, but ICs in those days were rather more modest on a per-chip basis than they are nowadays.

SeleniumFalcon

Several year ago I made a really dumb move by not buying an Otari from a friend who only wanted a couple of hundred for his. Similar to when, many years ago, I turned down an offer for a free Revox G36. I was a pig headed Sony fan and sniffed at it.
Anybody have a hot tub time machine they're not using?

SCompRacer

While it was in isolation I bought some inexpensive wood sides for a MX5050. They were rough, Aaron called them firewood. I did a half fast repair on them only to find mounting holes don't match up. Handles were removed to repair them. I sure wouldn't lift it with my fingers in them shallow pockets.

SCompRacer

I'm amazed how clean it is inside. Just some single spider webs here and there. While on it's back, remove bottom cover and two face panel screws and lower board pulls out and folds down. Some narrows strips of rolled paper towels were placed alongside switches to catch DeOxit that runs out. After application and a soak, they are repeatedly actuated. Then I used canned air to blow them out. There were small square holes to dribble DeOxit in.

I removed the potentiometers for a more limited, controlled application of DeOxit F5 fader. I didn't want to wash any grease out of the shafts.

I removed the narrow control panel for a controlled DeOxit application to the switches.

I have some Otari spec capstan oil ordered. Some say oil is oil, Otari techs tell me to get the real deal. The direct drive capstan motor has a rear ball bearing while the drive end has a bushing.

I did a variac power up, all looks good. Just did some basic play, FF, Fast Rewind. I have no two track tapes and I don't want to test record until I get the capstan oil.






Just the four push buttons on left that stick out were cleaned. The speed encoder was sealed.

schwarcw

It lives again!

SCompRacer

Still await the capstan oil but the VU meter bulbs arrived. OEM are frosted. Frosted are scarce and when found, sellers typically ask ~$15 to $25 each. I purchased five inexpensive clear for $14 shipped. Too cold outside for etching chemicals so I sanded them a bit to reduce the glare.

Otari did pin 3 hot on the XLR and had a notice silkscreened next to them. I was mulling my options as most gear these days is pin 2 hot. Thanks to Ken for pointing me to the AES14-1992 standard which is pin 2 hot or positive, pin 3 cold or negative. Made it easy to decide what to do.

Standard XLR to RCA adapters that I have would ground pin 3 to 1, the shield. Instead of making custom adapters/cables to connect pin 3 to center pin RCA, I swapped wires on pin 2 and 3 for output, input and mic XLR's. Big font on a label under them makes it obvious.

SCompRacer

Magic oil arrived. Operational testing may proceed. New RTM SM911 tape used. $56 bucks for 10.5 reel, Black Friday sale. Tech's have told me a two-track machine will not completely erase a four track recording.

Those front mounted bias, record level and EQ adjustments and built in 1kHz/10kHz oscillator are sure convenient. If you change tape type, you can quickly calibrate to it using VU meters.

Connected to old Yamaha CA-800 in basement system via SE, I had to turn input volume to max to achieve near 0VU peak levels. Carried it upstairs (62 pounds!), connected to ARC Ref 3 record out via balanced, and only need input knobs around 2 o'clock for 0VU peaks.

I have an issue to look into regarding a pinch roller noise using the back coated SM911. It's quiet using an older tape. The pinch roller is old so expect to get a new or send to Terry in MI for a new tyre. I thought I had a record problem but that was user error, failed to latch channel 1 record button.

Playback of recordings sounds verrrrry good. Tape sure runs by quick at 15ips though. If I keep this deck, I'd use 7.5ips. With two track you can only record one direction.

SCompRacer

Aaron had a week off and said pick a day go to the tree farm to make some nice side panels for the Otari MX-5050. It’s a long day at ~1:30 to Aaron and then another hour to the farm plus working the rough-cut wood.

Everyone seems to do dark wood for Otari sides so we chose some Cherry along with some nice Walnut. The chunk of Cherry I brought back to make matching footers didn’t make it through the planer so that's on the to do list. The Walnut sides are still in stages of finishing.





This deck came with rack mounts and had no footers. They sell reproduction plastic footers on ebay. I’ve seen 3D printed and ones machined from Delrin. Cost ~ $60 to $70. Some offer wood footers which look a bit nicer. These were made to exact length of 8.66 though I chose to make them a bit thicker (15/16”) than original. This deck weighs 62 pounds and the last thing you want is setting it down with your fingers under the side panels with thin footers.



Mount screws were countersunk and I installed metal washers to keep the narrower screw head from burrowing into the footer.



Plenty of screw thread engagement in base of deck.



The original footers were extended past the front of deck as it is front heavy. I’ve seen guys just have round footers on the bottom, but one accidental bump can send it falling on its face.




Instead of the original Allen head screws and cone cup washers (which are plastic) I chose some nicer looking aluminum shoulder washers and flat head M4 black stainless screws for a nicer finished look. I have some Allen head on the way to replace the Phillips head.




So long to the "firewood sides" as Aaron called them before I did some half fast repairs. They were purchased while the deck was in bagged isolation and were slightly smaller and not for a MX-5050 as advertised, but I drilled holes to make them fit. They were much better for carrying the deck around than the metal rack mounts. I opted for no carry handles in any of the new wood sides.

SCompRacer

The bevel edge Walnut sides done. IMO these tick the straight, wave and mountain grain boxes along with some nice coloring. That Aaron @ALL212 sure has an eye for picking wood in the rough.







Had some worm holes on one panel which I mounted to the left side rear. I decided to fill them with dark Walnut sawdust to celebrate the memory of the traces that worm left behind.

xschop

Those turned out schnazzy.

SCompRacer

Thanks!

Since I’m on a high after replacing Jay’s Mitsubishi LT-30 TT motor, I decided to remove and replace the ball bearings in the Otari MX-5050 BIII capstan motor. The bearings are ~31 years old and with a bearing stethoscope I could detect a slight noise, so best to replace.

The MR-1L motor was a perfected design over the earlier capstan motors. These can set you back ~ $400-$500.
Two NSK 629Z ball bearings at rear and a long bushing at front.








It looks like Otari pressed a sleeve on rear shaft to use a standard size bearing bore.




Early motors like in the BII could suffer from adhesives drying out and sensors dislodging and dragging on armature which could just cause noise or have you shopping for a used motor. Best practice for these is to remove, disassemble and add epoxy in the right places.

One other issue in some model Otari capstan motors (MX55 IIRC) is they required a special 629(X) ZZ with the (X) designating a custom bore. Last I looked Precision Motor Works had a limited quantity of the X bearings for $88 bucks each. I just need a standard bore 629 Z, much cheaper at ~ $20 for a pair.

EndersShadow

I don’t understand half of what you said but dam it looks clean and you seem to know exactly what needs done lol

SCompRacer

Sometimes I don't understand what I'm doing....

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SCompRacer

Thanks for the kind words Ivan!

Trouble in paradise. It seems I didn't research enough or look harder. The MR-1L motor in the BIII has the 629(X) custom bore bearings as the 1H motor. I'm guessing they enlarge the race ID before hardening and assembly. It would be risky to grind or machine down the motor shaft for standard bearings. Only a machinist could say if it's possible. The armature has magnets on front and back.

629(X) marked in the inner race means custom bore.



I sold all my micrometers and dial bore gauges to a buddy so all I have are these inexpensive dial calipers. It gets you close but I wouldn't call it take it to the bank exact. The difference between a 629(X) and 629Z, the 629(X) inner race ID is .025-.030" larger. The motor shaft is 9.00mm/.354." The design and assembly of the motor require slip fit bearings. IIRC 15ips is 923RPM and 7.5 is 460RPM.



The armature. One pic looked like a sleeve on ball bearing end of shaft but it was just lighting.




The old bearing stethoscope picked up what I call a dry bearing sound. After 31 years the grease could harden. The outer races spun really easy, almost freewheel, no slight resistance. I figure I'll try greasing them first.

Grease has to be baby bear right. Too thick and the slip fit races will spin on the shaft. Too thin and it could run out.



There is the old blob of grease on a piece of baggie, taped tightly around bearing and plug race and push down trick. I took the bearing to the hardware store and found a 3/4" PVC pipe cap was very close. Just wrap some tape around bearing for a snug fit. Much easier than trying to tape a small piece of a baggie with grease blob to the small bearing.



I don't have the Otari spec for grease, so I went with what most small sealed bearings are shipped with, NLGI 2. Viscosity is like a creamy peanut butter. NLGI 1 is like tomato paste. A grease pencil with tapered tip was perfect for plugging ID. A 3/8" wood dowel tapered at end is another possibility. It allows plugging the hole and turning the inner race while pushing down into grease.



Bearing manufacturers tell us that you don't want a 100% fill as it results in grease churning, adding resistance and heat. So I ran the bearing back and forth on a towel to run some excess out. The metal dust covers are pressed in so not much chance of getting them out without destroying them.



If this doesn't work, the alternatives are two $88 bearings from PrecisionMotorWorks. Athan Corp in CA says they will rebuild an MX-5050 capstan motor for $385, but they show a BII motor which uses standard off the shelf bearings. They haven't answered my inquiry if they have the special bearings for this motor. This deck is worth either investment.

SCompRacer

My bad...

.0025-.0030".

SCompRacer

While OEM labeled reels are not absolutely necessary, they are nice to have. OEM Otari reels are scarce. Used ones are typically beat up. No surprise considering they were a professional working deck. A tool, as mhardy6647 accurately described them.

Included with one of my deck purchases was a badly bent Teac reel.



I straightened the reel sides best I could. If I continued to flatten the crease it would stretch and warp the sides to where I wouldn't be able to flatten without shrinking the metal first.



Slight derail.... I don’t know who first came up with the loophole with pin in hub the OEM Teac reels have but they make attaching tape to take up reel so much easier. The Chinese are making them now with the hole but no stamped bent pin. With no pin you have to stick your pinky in there or a pencil eraser to hold the tape until you get a wrap around hub. Still easier than no hole.



Back to the creases. I sanded the area and filled them with glazing putty.



Sanded and painted with Rust-Oleum aluminum primer then their Satin black.



On Etsy I found someone in Croatia who makes vinyl stick on Otari letters. They are available in three sizes and several colors. They closely match the slant of the Otari logo and this is the closest color match.




This is the middle size I stuck on a reel of RTM SM911.



Looking closely at an OEM Otari reel I see they had a white border and background. The OEM Otari reels used smaller font and the font radiated out from center of hub than across. I am having a Chinese seller make me a silver and black reel with the exact cutouts (they are already offered in that style), no logo, to match the original. They don't offer the slanted letter option. I’ll get some smaller letters from Etsy and make them look like OEM.



For the black reel I used a piece of white Brother 24mm/1" TZ label tape and cut it to shape slightly oversize for a background and border.




Good enough for now.

BigDaddyJay

Quick question but how did you get the tape splicing block off the head cover to give it a paint job?

SCompRacer

The splicing block is Anodized aluminum, and it was held on with double sided tape. I used a thin bladed regular screwdriver to remove it. I started working it off a little at a time from one end, pushing the driver deeper working back and forth across the width. If it's pried too harshly the aluminum splicing block could bend. It was reattached with double sided tape.

SCompRacer

I finally received the small Otari stickers from Croatia. USPS must not like mail from there... Just a buyer....

https://www.etsy.com/listing/1792741410/otari-stickers-die-cut-vinyl-aufkleber

Got the reels from the Chinese seller on ebay. Reels were well packed individually in foam bags, in sturdy box with dense foam between the reel sides. This seller was very accommodating. They did them in the cutout I wanted with loopholes, one silver, one black and no logo. No affiliation other than buyer.

https://www.ebay.com/itm/136452600426



Loopholes to make tape threading easy, but no stamped anchor pin like the Teac reels had. Still better than no holes.



These will be used as take up reels, gives me two color options.



An OEM reel on ebay, priced too high for condition IMO.

SCompRacer

I finally scored a reasonably priced Otari MX-5050 BII-2 head block with 4T playback head. This was standard on a BII but optional on a BIII. It will plug right into a BIII-2 deck. I’ve seen them sell for $300-$500. I got this one for $221 shipped. Heads are worn but not worn out. They do need lapping before installing and aligning on a different deck. This option will slightly increase the value of deck and make it a bit more desirable to a buyer as you can play 4T track tapes on a 2T deck but not record 4T.



BII block above mine. Since my heads have little wear I may just remove the fixed guide, move the erase head to end, align, lap and install 4T playback head/align on mine. That way I won't have to calibrate deck to different 2T heads. The 4T head runs with the 2T calibration. I would need~ $1,000 in MRL calibration tapes to calibrate deck. (One 3.75, two 7.5 NAB/IEC EQ, two 15IPS tapes NAB/IEC EQ).

Top block from L to R, 2T reproduce, 2T record, 4T reproduce, erase.



It takes some effort to arrange lighting to take a really good pic of head that shows wear without glare, especially with shields shrouding repro heads, so just the 2T record head from the ebay block is shown. The other two are similarly worn.



Common issue with these, the 2T/4T switch is very dirty. I don't know why they cheaped out here with an open on each end slide switch. The great majority of switches have copper or silver contacts which will oxidize and cause resistance or even open-circuit.



I got it cleaned up, ohms out good. But for how long...



While they use a 4PDT, you don't really need one. Maybe for super strain relief for aggressive switch sliders. Or they figured it would get dirty and added more contact real estate. I was hitting the data sheets and it's hard to find a DPDT with that pin spacing. You can see by the traces two short gold contact SPDT switches are all that is needed and easier to adapt to that pin spacing. I can cobble together some strain relief if needed. The gold plated switches are more expensive than silver plated contacts, like $10-12 each. They are sealed but not hermetically and the gold won't oxidize.

The switch body also connected two ground planes. My head block with no switch had jumpers.



B-2LD schematic at left applies to the BII-2 head block.

SCompRacer

I lapped the worn heads and the 2T reproduce and 2T record came out nice. You have to rotate the head while dragging on sandpaper to maintain head profile. I have a sloped board I place across laundry tub and run water on wet dry sandpaper sitting on thick piece of flat glass while lapping.



The 4T reproduce went open gap. This can happen with worn heads. Sometimes they wear into open gap or you find it when you remove material to get rid of wear groove by lapping. If you ever buy used heads, get good pics. Many sellers do not take good, detailed pics of heads.



My options are gamble by purchasing a used head that will fit and lap it. Technics RS 1500 and Pioneer RT 909 heads are similar mounting and will work. Otari 4T heads are scarce. There is a seller on ebay that offers a new head for Pioneer that fits Otari. It’s a 4T core in a 2T body for $200.

I consulted with an Otari specialist, and he said just about any 4T playback head that will fit will work. It’s the record heads that are touchy. I have some lapped Teac X-1000r play heads here, won’t cost me anything. Comparing inductance, the Otari 4T head measured ~ 450mH while the Teac is 550mH. Trouble with the Teac head is different mounting screw location and they are slightly wider spaced.

The heads need to be positioned at the correct height or you’ll lift the tape off adjacent heads, the 2T record and erase head in this case or be too low for tape to contact head.

I told my best layout man to lay of the coffee and mark and dill new holes in the head mount bracket. The holes cannot be too big as they are secured with 2mm x 5mm screws so proper placement a must. I clamped the heads together tape contact side down and marked the mounting difference on the Otari head. I measured the difference, center punched and drilled new holes in the head bracket.


Luck is where preparation meets opportunity… I did good. Next up mount the head on block, align head with clear leader tape, plug it into deck and run calibration tones for azimuth. They make head height tapes for really fine tuning. Typical calibration tapes are full track where a head height tape just has separate tracks.



Image snagged from JRF Magnetics.




https://www.jrfmagnetics.com/index.html?JRF_mainframe=/JRF_relapping.html

Lapping board.