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‒ B503 = a 50 kΩ potentiometer whose nominal taper is “B”.
‒ 216c = a manufacturer-internal code (date / lot / factory / revision); it has no influence on the electrical specification.
Key points
• “503” → 50 × 10³ Ω = 50 kΩ
• First letter (“B”) defines the taper; most modern Asian/JIS parts use B = linear, but older IEC parts use B = logarithmic. Check the data-sheet if taper is critical.
• The trailing “216c” string is only for traceability.
Resistance code
503 → 50 × 10³ Ω = 50 kΩ (EIA-96 / IEC 60062 three-digit scheme).
Taper code
• JIS / AEC (used by Bournes PTV, Alpha, Piher, many SMT trimmers):
A = log (audio), B = linear, C = reverse log.
• Older IEC / European carbon track pots (e.g., Piher PC16 from the 1980-90s):
A = log, B = log (European “B-curve” = semi-log), C = linear.
Because almost every low-cost 9 mm / 16 mm potentiometer you buy today comes from Asia and follows the JIS rule, B is almost always linear in currently-sold components.
➔ If the part is pulled from recent Asian equipment, assume linear. If it is from vintage European gear, confirm before substituting.
Secondary string “216c”
• Not part of any international marking convention.
• Commonly encoded as YWWR or YYWW, where Y = year, WW = week, R = revision/batch letter.
• Example: 21 6 c → 2021, week 6, lot c (but exact decoding depends on the maker).
• Electrical designers can ignore it unless traceability or warranty is involved.
Why the terminal “c” is not a taper code
• Taper letters appear before the resistance digits, not after.
• Reverse audio pots are marked “C503”, “C50k”, etc.—the “C” precedes the value.
• Therefore “216c” cannot indicate a reverse log taper.
• Nearly all panel-mount and SMT trimmer pots from major vendors (Bourns, Alps Alpine, Alpha, TT-BI) currently ship with JIS lettering.
• Digit stamping is being augmented by laser engraving; secondary codes now often include QR-like dot grids for automated optical traceability.
• IoT appliances favour digital potentiometers (digipots) for field calibration; classic carbon pots remain dominant in cost-sensitive analog front ends and musical instruments.
Mathematical relation (resistance coding):
\[ R = (D_1 D_2) \times 10^{D_3}\ \Omega \]
For “503”: \( (5,0) \times 10^{3} = 50\,000 \Omega \).
Practical example:
A synthesizer’s filter cutoff knob labelled B503 will sweep the filter with a linear control law if the pot is really B-linear. Replacing it with an A503 (log) would compress most of the action into the last 20 % of rotation—unwanted in this context.
• Traceability codes such as “216c” support recalls under ISO 9001 and IEC 60068; do not remove them on safety-critical assemblies.
• Substituting a different taper in consumer audio equipment affects user experience but is not safety-critical; in medical devices it can violate IEC 60601 usability clauses.
• To verify taper quickly, set the shaft at 50 % and measure wiper-to-end resistance; a linear 50 kΩ pot will read ~25 kΩ.
• When ordering replacements, specify both resistance and taper explicitly (e.g., “50 kΩ, linear, 20 mm shaft, PCB pins”).
• If in doubt, download the vendor’s data sheet; identical value codes from different vendors may differ in mechanical life, power rating, or sealing.
Potential challenges & mitigation
• Conflicting taper conventions → consult data-sheet or measure.
• Obsolete value → use series/parallel resistors to trim if exact 50 kΩ is unavailable.
• Mechanical mismatch → 3-D print adapters or buy Econopot “break-off” shafts.
• Power rating is not encoded; common 16 mm pots handle 0.1–0.25 W.
• Temperature coefficient, contact noise index, and rotational life are also unspecified by the B503 code—important for precision instrumentation.
• Investigate digital potentiometers (e.g., Microchip MCP41xxx) as replacements when microcontroller control or calibration memory is desired.
• Study conductive-plastic vs. carbon-track technologies for better lifetime in pro-audio faders.
• Review IEC 60393-1 (potentiometer test methods) if designing for harsh environments.
“B503” tells you the essential electrical data: 50 kΩ total resistance, taper “B” (almost always linear in modern stock). “216c” is only a production/date code, irrelevant to circuit design. Always confirm the taper standard used by the manufacturer if you are substituting parts in a design where the law of control (linear vs. log) matters.
