Product Overview
HP 1854-0071 Proprietary NPN Silicon Transistor - Original House-Numbered Part for Vintage Test Equipment Restoration
Condition
Unused NOS. Photos show the TO-92 plastic body marked "4-071" and date/lot code T1808, with three straight leads showing light tarnish consistent with age - should clean up with standard lead prep. Small circular index mark visible on face. Sourced from an electronics distributor consolidating inventory. Evaluation: Visual inspection only. Function testing not performed.
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Product Overview
Hewlett-Packard 1854-0071 is an HP house-numbered NPN silicon bipolar transistor in a TO-92 plastic package. The 1854 prefix in HP's internal part numbering system designates a standard bipolar silicon NPN transistor. The face is marked "4-071" with date/lot code T1808. HP specified this component as a high-reliability switching and drive transistor across a range of their classic instruments, and finding original HP-numbered stock is the difference between a clean restoration and a cross-reference gamble.
Key Features
- Transistor type: NPN silicon bipolar junction transistor (BJT)
- Package: TO-92 plastic encapsulated
- HP house part number: 1854-0071 (face marked "4-071")
- Date/lot code T1808 visible on package face
- Three-lead TO-92 configuration - emitter, base, collector
- Intended application: high-reliability switching and signal drive within HP test equipment circuits
- Leads show light tarnish consistent with age - standard lead preparation recommended before soldering
Applications
- Restoring an HP 606B signal generator - replacing transistors in the power supply unit to address power regulation issues using the original HP part number rather than a cross-referenced substitute
- Repairing an HP 5343A microwave frequency counter - replacing the 1854-0071 in EECL-to-TTL converter circuits where gain and pinout matching to original spec matters
- Servicing HP 7970 series digital magnetic tape drives where this transistor was used as a switching and drive component
- Bench restorers maintaining historical accuracy in vintage HP instruments - original HP part numbers preserve calibration integrity when generic equivalents introduce uncertainty
- Makers and hobbyists using a verified TO-92 NPN from a known production lot as a reliable general-purpose switching transistor in DIY circuits or breadboard experiments
Frequently Asked Questions
What HP instruments used the 1854-0071?
Confirmed applications include the HP 7970 series digital magnetic tape drives, HP 5343A microwave frequency counters, and the power supply section of the HP 606B signal generator. The HP 606B service documentation also identifies the 1854-0071 as a selected 2N3704.
Why not just use a 2N3904 or other cross-reference?
HP sourced the 1854-0071 from multiple manufacturers - including Texas Instruments and Motorola - and in some production runs the pinout varied between suppliers. Generic cross-references like the 2N3391, 2N3904, or NTE123AP may carry similar electrical characteristics but can differ in pinout and gain selection. When restoring sensitive calibrated test gear, an original HP-numbered unit removes the guessing entirely.
What is the pinout for this transistor?
The pinout can vary depending on which manufacturer produced a given lot of 1854-0071 for HP. Check the service manual for your specific instrument to confirm the intended emitter-base-collector orientation before soldering. The circular index mark on the face provides a reference point for orientation.
Is this a single transistor or a lot?
Please check the quantity field on the listing for the number of units available.
Are there any electrical specs confirmed for this part?
Transistor type is confirmed NPN silicon. Package is confirmed TO-92. The HP 606B service documentation identifies these as selected 2N3704 transistors. Exact Vceo, Ic, power dissipation, and hFE values for this specific lot are not confirmed. Buyers should reference the service manual for their instrument to verify suitability.
An original HP house number on a TO-92 is a small thing with a long memory - the technician who needs this knows exactly why the cross-reference won't do. Put it back where it belongs.
