Identifying a first-generation MX-5050
Is it an early MX-5050? The two-channel Mini Pro is one member of a wider first-generation line. Otari also sold the quarter-inch four-channel QX/QXD and the half-inch eight-channel 8/8SD. Before you buy parts, download manuals, or follow repair advice, confirm both the model and the tape format.
The two-channel cues below are checked against my own deck; the wider-format examples come from Otari's period documentation. If you want the family tree, the generation table on the history page is the one-screen version.
In the line-up↑ TOP
The fronts change with the format. A two-meter upright does not stand for every first-generation machine: Otari's QXD documentation shows four-channel electronics, and the 8SD manual photographs an eight-channel transport with its electronics in a separate case. The 1978 line-up advertisement also names the quarter-inch QXHD and half-inch 8D beside the two-channel 2S.
Track-format examples
Click an image to enlarge it. Meter count shows channels: a quarter-track stereo deck can still have only two meters.
2S / Mini Pro
⤢ zoom- Tracks
- 2
- Channels
- 2
- Tape
- ¼″
QXD
⤢ zoom- Tracks
- 4
- Channels
- 4
- Tape
- ¼″
8SD
⤢ zoom- Tracks
- 8
- Channels
- 8
- Tape
- ½″
The QXD image is a factory equipment drawing, not a photograph; the 8SD is a factory manual photograph. Confirm the exact model on its identification plate.
Here tracks means the recording format; my 2S can also reproduce quarter-track tape. The 4S is quarter-track stereo: four tape tracks but only two channels, so four meters would be the wrong visual test. The full-track F is mono. We do not yet have securely identified whole-machine photographs for those two formats; their head blocks and model plates matter more than a front view.
The QXD manual's equipment drawing includes the 2SD₂ table-top console as well. That two-channel model, and the related half-inch ½QXD, belong with the Mark II. Two boxes alone cannot decide between these families; read the model code on the identification plate.
The two-channel upright's silver backed plate↑ TOP
On the two-channel upright shown here, the silver backed plate sits behind the knobs and level meters. Mine wears rack-mounting brackets instead of the factory wood side panels. This is a useful comparison with the plain B, whose lower electronics faceplate is black; it is not a rule for every QXD or 8SD configuration.
The back of my deck: the factory wood case, with the rear jack panel recessed into it
The wood isn't just trim on this example — the whole case is timber. The two-channel model was offered with a walnut finish, portable case or rack kit. Here's mine from the back, with the jack panel recessed into the case. The yellow Klarion sticker beside the AC inlet is a period marker of its own — Klarion Enterprises of South Melbourne was the Australian distributor named in Electronics Australia's June 1976 review.
The face badge↑ TOP
Start with what the badge cannot tell you, because this is the pitfall
that sends people down the wrong path: the face badge does not carry the
model suffix — on any generation. Photographs of B, BII, BIII, MKIII and
MKIV machines, each checked against its own rear plate, all show the same
thing: a bare MX-5050 on the transport panel. A deck whose rear plate
reads MX-5050BII-2 or MX-5050 MKIII-2 still shows you nothing but
"MX-5050" from the front.
So the reasoning you'll see in forum threads and sellers' listings — "it doesn't say B on the front, so it's a Mark I" — rests on a marker that doesn't exist. A bare badge is not evidence of anything. The suffix lives on the rear plate.
What the badge can do is two things. The first is the best single marker on the whole machine — because on some first-generation decks, Otari printed the nickname straight onto the front:
The badge on a first-generation MX-5050: MX5050 in white italic script above a blue rule, with MINI PRO in blue outlined capitals directly beneath it
Badge detail from a wood-cased 1975 machine photographed by Ottermel — Tapeheads.net.
MINI PRO, in blue outlined capitals, silk-screened directly beneath the logotype. No later machine wears it. If you find that on a faceplate, you are looking at a first-generation deck and the identification is over — it is the one badge marking that settles the question by itself. It is also the proof that "Mini Pro" was never collector slang: Otari put the name on the machine. The first generation's own history traces the same name through the trade press and Otari's own advertising.
The same second line shows on the US-market 2SH photographed in Audio's April 1976 review — too coarse in the halftone to read, but plainly there under the badge in both of the review's photos.
The catch is that not every first-generation machine has it. Mine doesn't — just the bare underlined logotype — and neither do several other documented first-gens. So the rule runs one way only: MINI PRO under the logotype is proof of a first-generation machine; its absence proves nothing at all. What separates the two styles — production date, market, or a running change on the line — is still an open question. If your machine wears the MINI PRO badge, a photo and the serial number would be gratefully received; enough of them and the pattern would fall out.
The second thing the badge tells you is the era, through how it's made rather than what it says. On the two-channel upright examples here, the logotype is italic script, underlined, as in the photo above. The BII/MKIII-era machines print an upright, outlined MX-5050 centred on the transport panel. By the BIII/MKIV era it is an embossed silver plaque at the right-hand end of the panel. Same seven characters every time; three different pieces of industrial design. (The MKIII and MKIV are not later generations than the BII and BIII, incidentally — they are their desk-top siblings. That story is the wider family.)
The record buttons: a test you can run on a photograph↑ TOP
This test is for a two-channel upright like the one photographed above. Most listings show only the front. The record-ready buttons can distinguish that early panel from a BII or later two-channel panel, but do not apply this two-button test to a QXD or 8SD with separate electronics.
The record-ready buttons on a first-generation deck: the two red RECORD CH1 and CH2 caps butt directly against each other, forming a single continuous red bar, and the black SEL/REP pair beside them does the same
First, be sure you are looking at the right red buttons. There are two sets. The ones that matter are the record-ready pair on the electronics panel — labelled RECORD CH1 / CH2, down among the level knobs, as in the photo above. The other red button, up in the transport row beside PLAY and STOP, is the REC key, and it is no help at all: measured across the generations, a first-gen, a B, a BII and a MKIII all wear much the same wide red key. (It does change at the BIII and MKIV — going square, with a symbol instead of a word — which is the opposite direction to the record-ready buttons, and a fine way to confuse yourself.)
Now: do the two red RECORD-READY buttons touch?
- Touching — butted against each other into one continuous red bar, each cap about half again as wide as it is tall — on this two-channel upright narrows the choice to a first-generation 2S or an MX-5050B.
- Separated — a gap of roughly one and a half button-widths between two square caps — means a BII, BIII, MKIII or MKIV. Otari redesigned the whole switch family at the BII, and the black SEL/REP pair beside them changed in exactly the same way, so it doubles as a cross-check.
Measured across eleven two-channel machines — eight of them confirmed by their own rear plates — the gap was zero on the sampled first-generation and B panels, and one-and-a-half to two button-widths on the sampled BII and later panels, with no overlap. Adjacency is the right thing to measure, too: a gap and a width are both horizontal lengths on the same panel, so their ratio survives a photograph taken at an angle, where an aspect-ratio measurement would be distorted by the perspective.
Be clear about what this buys you, though. For a two-channel upright, it is a negative test: square, separated buttons rule out the early 2S panel. Touching, rectangular buttons narrow it to first-generation 2S or B — and then you still have to settle it with the faceplate and rear plate.
The model reference — read the rear plate↑ TOP
Since the face won't tell you, this is where identification actually happens. Find the model code on the identification plate. The early line includes 2S, 4S, QX/QXD, F and 8/8SD codes, with speed and drive suffixes; mine reads 2SHT. The model list gives the documented codes and tape formats. A B, BII, BIII or MARK code points to its own guide, but the shared QXD manual also prints 2SD₂ and ½QXD: those separate-electronics variants are covered on the Mark II page.
The model plate on my deck's rear jack panel: OTARI MX5050 TAPE DECK, model 2SHT, AC 240 V 50 Hz 80 W, serial no. 17707038 — Otari Electric Co., Ltd., made in Japan
The serial number dates the machine
The plate gives you more than the model. The second and third digits of the
serial number are the year of manufacture. Mine reads 17707038 —
1977 — and the TOWA capacitors inside are date-stamped 1977, which is a
second, independent witness on the same deck.
I did not originate this rule: it comes from a single forum post, offered without evidence, and on its own that is not enough to publish. So I tested it against every MX-5050 I could find whose generation is settled by its own rear plate, never by the serial:
| Machine (identified from its rear plate) | Serial | Digits 2–3 | Implied year | Consistent? |
|---|---|---|---|---|
| First-generation 2SHT (mine) | 17707038 | 77 | 1977 | ✓ first gen ran 1974–78 — and the caps agree |
| MX-5050 BII-2 | 18690154 | 86 | 1986 | ✓ BII era |
| MX-5050 MKIII-2 | 18630546 | 86 | 1986 | ✓ MKIII-2 from 1983 |
| MX-5050 MKIV-2 | 19452149 | 94 | 1994 | ✓ MKIV from ~1990 |
Four machines, four generations, four years that each land inside the right
production window — and rising in step with the generations. That is enough to
use, with two honest caveats: the sample is four, and what the leading 1 and
the trailing digits mean is anyone's guess.
If you send me a serial with a photo, you extend that table — and if your deck wears the MINI PRO badge, you also help settle when Otari stopped printing it.
Mine reads 2SHT, a designation Electronics Australia decoded when it reviewed this exact model in June 1976: 15 and 7.5 in/s tape speeds — as built; mine now runs 7.5 and 3¾, because a previous owner fitted the low-speed motor pulley and belt and left the plate alone (see the log) — with a four-head assembly — erase, ½-track record, ½-track playback and ¼-track playback, behind a playback changeover switch. And critically: no B and no MARK number anywhere on the plate. Above it sits the empty remote socket, as the deck arrived — the one the dummy plug now lives in.
The AC capstan motor↑ TOP
On my two-channel 2S, the capstan motor is powered by AC — a hysteresis-synchronous motor that locks to mains frequency. This is not a first-generation-wide test: DC-servo variants include the 2SD/4SD in the maintenance manual and the QXD and 8SD in OIM-1004E.
Three AC motor-run capacitors from the MX-5050: TOWA MP condensers, 250 WV.AC, dated 1977. The smaller 2+0.5 µF (left) is the capstan motor's run cap — it rules out the DC-servo direct-drive machines, though the plain-B 2H/2L/4L kept an AC capstan too. The two 5.5 µF serve the reel motors, which stayed AC induction on every later model, so reel-motor caps alone prove nothing.
You'll find the AC motor-run cap near it — mine carried TOWA "MP condenser" cans: a 2 + 0.5 µF for the capstan motor and a pair of 5.5 µF for the reel motors, all rated 250 WV.AC and dated 1977. Be precise about what the capstan cap tells you: a DC-servo direct-drive capstan has no run cap, so finding one rules out every BII and BIII and the D-suffix B models — but the plain MX-5050B 2H, 2L and 4L kept an AC synchronous capstan. Treat it as supporting evidence next to the silver plate and the model reference, not as proof on its own. What replacing these involves — including how to make a 5.5 µF that nobody sells any more — is in Re-capping the motor run caps.
The capstan flywheel inside the MX-5050 transport
On this 2S, the capstan is belt-driven with a flywheel — the motor does not turn the capstan shaft directly. Do not expect that drive layout on a QXD, 8SD, or another documented DC-servo variant.
The P-12 speed board
P-12 speed board with different capacitor values marked for 50 Hz and 60 Hz mains. Note: this board is already re-capped — I fitted a single 2.5 µF motor-run cap, which is all I need at 50 Hz, so only two legs are wired in. On an unrestored unit you'd see all three contacts coming through.
Supporting evidence if you're inside the machine anyway: the P-12 speed board is marked with different capacitor values for 50 Hz and 60 Hz mains — a distinction that only matters to a mains-synchronous AC motor.
If it doesn't match↑ TOP
If your machine lacks the two-channel silver panel or its touching record buttons, it may still be an early QXD or 8SD. The 2S/4S maintenance manual does not cover those machines; their own instruction and maintenance books do.
Work out the model from its identification plate, then read across the generation table: a plain-B 2H, 2L or 4L still has the AC synchronous capstan and the belt, so a fair amount here still applies to it. If the plate carries a MARK number, start with the wider family — those machines are the B series' desk-top siblings, and a MKIII-2 shares its heads and audio board with a BII.