BCY79-VII - PNP 45V 100mA Low Noise TO-18 | Central Semiconductor
MPN: BCY79-VII β End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $1.42 | $1.42 |
| 10 | $1.28 | $12.80 |
| 100 | $1.05 | $105.00 |
| 500 | $0.88 | $440.00 |
| 1,000 | $0.72 | $720.00 |
BCY79-VII Overview
A bipolar junction transistor is a three-terminal current-controlled semiconductor device that amplifies or switches electronic signals. Within the component hierarchy, the BCY79-VII belongs to the small-signal BJT family: transistor -> bipolar junction transistor -> PNP general-purpose transistor -> discrete semiconductor. PNP devices conduct when the base is pulled low relative to the emitter, making them the complementary counterparts to NPN types in push-pull stages and differential pairs.
Key features include a low-noise figure suited to audio input stages, the hermetic TO-18 metal case that provides superior shielding and thermal stability versus plastic packages, and the -VII gain group selection (part of the BCY79 VII/VIII/IX/X hFE binning scheme) that guarantees predictable DC current gain for precision analog design. The 5V emitter-base rating and 200C maximum junction capability (per the Central Semiconductor family datasheet) support demanding legacy designs.
The epitaxial planar process delivers a 100MHz transition frequency, adequate for RF amplification up to VHF and fast small-signal switching. Because the die is sealed in metal, leakage currents remain low across temperature, benefiting high-impedance input stages in instrumentation.
Typical applications include low-noise audio preamplifier input stages, driver stages in analog signal chains, switching circuits in industrial legacy equipment, and RF/VHF small-signal amplification. Philips (now NXP) originally manufactured the BCY79 family; Central Semiconductor continues production for the aftermarket.
Design consideration: respect the 340mW package dissipation at 25C free air and derate above ambient; verify pin orientation (TO-18 pinout) before drop-in replacement because TO-18 lead arrangements vary across families.
This page synthesizes distributor pricing, drop-in alternatives, pinout data, and practical design notes not found in the manufacturer datasheet, with per-day verification against live web data.
Drop-in alternatives for BCY79-VII β same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with BCY79-VII (same form factor and footprint) β differing in Configuration, Emitter-Base Voltage (VEBO), Package, Transistor Type.
Quick Comparison Tool β Select alternative parts for side-by-side comparison:
BCY79-VIII
β Drop-Inπ Reference alternative (not in catalog)
BCY79-IX
β Drop-Inπ Reference alternative (not in catalog)
BCY79-X
β Drop-Inπ Reference alternative (not in catalog)
BCY79-VII PBFREE
β Drop-Inπ Reference alternative (not in catalog)
BCY78-VII
β Drop-Inπ Reference alternative (not in catalog)
BCY79-VII
β Drop-Inβ In Stock
$0.72 / Unit
View Datasheet βBCY79-VII Maximum Ratings & Electrical Characteristics
| Polarity | PNP |
| Transistor Type | Bipolar (BJT), epitaxial planar silicon |
| Collector-Base Voltage (VCBO) | 45 V |
| Emitter-Base Voltage (VEBO) | 5 V |
| Maximum Collector Current (IC) | 100 mA |
| Power Dissipation (PD) | 340 mW |
| Total Device Dissipation (DigiKey listing) | 1 W |
| Transition Frequency (fT) | 100 MHz |
| hFE Gain Group | VII (BCY79 VII/VIII/IX/X binning) |
| Package | TO-18 (TO-206AA), hermetically sealed metal case |
| Mounting Type | Through Hole |
| Configuration | Single transistor, 3-pin |
| Maximum Operating Temperature | 200 C (junction, per family datasheet) |
| Application | Low noise amplifier and switching |
| Lead-Free / RoHS Option | BCY79-VII PBFREE variant available (DigiKey/Mouser) |
| Series | BCY78 / BCY79 (VII, VIII, IX, X) |
BCY79-VII Pin Configuration
| Pin 1 | Emitter β Emitter terminal (PNP; connected toward supply negative in common-emitter use) |
| Pin 2 | Base β Base control terminal; pull low relative to emitter to turn device on |
| Pin 3 | Collector β Collector terminal; case is electrically connected to collector in TO-18 metal can |
Typical Applications
BCY79-VII is suitable for 6 applications: Low-Noise Audio Preamplifier Input Stages, Analog Signal Chain Driver Stages, Low-Speed Switching Circuits in Legacy Industrial Equipment, RF and VHF Small-Signal Amplification, Instrumentation High-Impedance Input Front Ends, Automotive and Marine Legacy Electronics Repair.
Low-Noise Audio Preamplifier Input Stages
The BCY79-VII was explicitly designed for low-noise amplifier duty, and Philips application literature names audio input stages as a primary use. Its PNP polarity suits common-emitter and differential front ends fed from positive supplies, while the 100MHz transition frequency provides ample closed-loop bandwidth margin. The hermetic TO-18 metal can shields the die from electrostatic and RF pickup, protecting the noise floor in microphone preamps and phono stages. Use the -VII gain bin where the bias network was designed around its hFE window; with 45V VCBO, the device also tolerates higher-voltage tube-hybrid and professional +30V audio rails that exceed the ratings of many plastic-packaged BC5xx equivalents.
Recommended
Analog Signal Chain Driver Stages
In analog driver stages, the BCY79-VII provides 100mA collector current capability with predictable hFE from the VII bin, enabling stable bias without aggressive feedback. The 45V collector-base rating supports 24V industrial analog rails with headroom, and 340mW dissipation at 25C covers small-signal drive duties. Philips literature lists driver stages among the intended uses of the BCY79 family. Designers should derate power above 25C ambient and keep VCE at moderate levels when driving near the 100mA limit. In complementary push-pull output stages, pair the BCY79-VII with an NPN driver of matching fT and package to preserve symmetry.
Recommended
Low-Speed Switching Circuits in Legacy Industrial Equipment
The Central Semiconductor datasheet classes the BCY78/BCY79 series as suitable for switching applications, and Philips datasheets title the family PNP switching transistors. With 100mA collector capability and a 5V emitter-base rating, the BCY79-VII handles relay-driver, indicator, and level-shifting duties in legacy industrial control boards designed when the Philips BCY79 was a catalog standard part. The hermetic TO-18 can resists moisture ingress better than plastic packages, supporting equipment in humid or harsh environments. Because the part is now EOL, maintenance engineers repairing such equipment should secure stock or qualify BCY79-VIII/IX/X as pin-compatible substitutions within the same footprint.
Recommended
RF and VHF Small-Signal Amplification
With a 100MHz transition frequency, the BCY79-VII provides useful gain through the HF band and into low VHF for receiver front ends, IF strips, and oscillator stages in legacy communications equipment. The metal TO-18 package grounds naturally to shielding structures and reduces parasitic feedback versus plastic leads, improving stability at RF. Because the device is PNP, it suits positive-ground oscillator topologies common in older designs. Noise performance from the epitaxial planar process keeps the noise figure acceptable for receive-chain use. Keep operating point moderate - the 340mW limit at 25C bounds available output - and verify hFE bin (VII) against the bias network when restoring period-correct radio equipment.
Recommended
Instrumentation High-Impedance Input Front Ends
The hermetic seal of the TO-18 metal case keeps leakage currents low and stable across temperature and humidity, which matters in high-impedance measurement front ends where bias current error dominates accuracy. The BCY79-VII's defined hFE window (bin VII) lets designers bound input bias current in differential pairs used for electrometer-style buffers and data-acquisition inputs. The 45V rating tolerates over-range input excursions on 24V-based industrial instruments. For best results, match transistor pairs from adjacent bins (VII/VIII) on the same die family to minimize offset drift. As the part is EOL, new instrument designs should consider current-production low-noise PNP alternatives and reserve BCY79 for legacy service.
Recommended
Automotive and Marine Legacy Electronics Repair
Hermetic metal-can transistors such as the BCY79-VII were widely used in 1970s-1990s automotive ECUs, marine instruments, and avionics where humidity, vibration, and temperature swings exceeded plastic-package capabilities. The 200C maximum junction temperature and TO-18 mechanical robustness suit under-dash and engine-bay-adjacent modules. Repair technicians restoring such boards need the exact VII hFE bin in circuits where bias was factory-trimmed; otherwise BCY79-VIII/IX/X drop directly into the same TO-18 footprint. Note the through-hole leads require careful soldering to avoid mechanical stress on the glass-to-metal seal, and the part's EOL status makes stocking spares advisable for fleet-maintenance operations.
Recommended
Recommended Products Summary
Engineering reference data for BCY79-VII β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | BCY79-VIII | BCY79-IX | BCY79-X | BCY79-VII (Philips/NXP) |
|---|---|---|---|---|---|
| Package | TO-18 hermetic metal can | TO-18 - same | TO-18 - same | TO-18 - same | TO-18 - same |
| Brand | Central Semiconductor | Central Semiconductor | Central Semiconductor | Central Semiconductor | NXP Semiconductors (Philips) |
| Polarity | PNP | PNP | PNP | PNP | PNP |
| VCBO | 45 V | 45 V | 45 V | 45 V | 45 V |
| Max Collector Current | 100 mA | 100 mA | 100 mA | 100 mA | 100 mA |
| Power Dissipation | 340 mW | 340 mW | 340 mW | 340 mW | 340 mW |
| hFE Gain Group | VII (lowest bin) | VIII | IX | X (highest bin) | VII |
| Transition Frequency (fT) | 100 MHz | 100 MHz | 100 MHz | 100 MHz | 100 MHz |
Key Differentiators
- Hermetic TO-18 metal can with case at collector (vs BCY79-VIII)
- Guaranteed hFE bin (VII) for predictable bias (vs BCY79-IX)
- Dual-sourcing heritage with Philips/NXP (vs BCY79-VII (Philips/NXP))
Design Notes
Confirm TO-18 pin orientation before substitution: the BCY79 uses pin 1 = emitter, pin 2 = base, pin 3 = collector (case at collector), but other TO-18 families use different arrangements (e.g., collector-base-emitter sequences). Soldering the device with reversed E/C will invert beta and may exceed VEBO, destroying the emitter junction. Always verify against the Central Semiconductor BCY78-79 datasheet diagram rather than assuming universal TO-18 pinout conventions.
Estimated: at the 340mW full rating with a typical TO-18 junction-to-ambient thermal resistance on the order of 300-350 C/W, junction rise approaches 100-120 C above a 25C ambient, leaving little margin to the 200C family limit in hot enclosures. Derate dissipation linearly above 25C and keep continuous dissipation under roughly 150mW in sealed, high-ambient equipment. In switching duty, ensure saturation (forced beta of 10) so the die does not linger in the high-dissipation linear region.
In low-noise input stages, source impedance drives noise performance: match the collector current to the datasheet noise-optimum operating point region rather than running maximum current. In the hermetic metal can the case is at collector potential, so mount the can away from unshielded wiring or isolate it to avoid capacitive coupling. When matching differential pairs, select transistors from the same hFE bin and, ideally, the same date code to minimize offset and drift.
Compliance Information
Central Semiconductor offers a PBFREE (lead-free) variant of BCY79-VII listed at DigiKey and Mouser, indicating RoHS-relevant lead-free compliance for that suffix. Compliance status of the legacy standard suffix is not stated in the provided data.
