Transistor BF858 NPN, 300V TO-202

Transistor BF858 NPN, 300V TO-202

Transistors

Reference: TRBF858

Part.No: BF858

€1.20

In Stock

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The BF858 is an NPN high-voltage bipolar transistor in a TO-202 package, designed for video output amplifier stages in CRT televisions and monitors. It provides the high breakdown voltage needed to drive the RGB electron guns of the picture tube.

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Description
Product Details

BF858 High-Voltage NPN Video Output Transistor for CRT TVs

The BF858 is an NPN high-voltage transistor used almost exclusively in the RGB video output stage of colour CRT televisions and computer monitors from the 1990s and 2000s. It sits on the tube's neck board (one per colour channel) and is responsible for driving the picture tube with the amplified video signal, which is why a fault in one of these transistors typically shows up as a missing or discoloured colour on screen.

Functions & Applications

High Breakdown Voltage: Withstands the elevated voltages present on the tube's video output stage without breakdown.
TO-202 Package: Robust through-hole plastic package that can be mounted directly on the neck board with minimal cooling.
Dedicated Video Application: Purpose-built for RGB output driving, unlike general-purpose small-signal transistors.
Common CRT Repair Part: Frequently used to fix single-colour loss or discoloured picture faults in vintage TVs and monitors.

Technical Specifications

Parameter	Value / Specification
Transistor Type	BJT (Bipolar Junction Transistor)
Polarity / Channel	NPN
Package / Case	TO-202
Collector-Emitter Voltage (Vceo)	~300V
Max Collector Current (Ic)	~0.1A
Power Dissipation (Ptot)	~1.5W (free air)
Typical Application	CRT TV / Monitor Video Output Stage
Mounting Type	Through-Hole (THT)

Frequently Asked Questions

Q: If one colour disappears from my CRT TV picture, could the BF858 be the cause?
A: Yes, this is a very common cause. There are usually three of these transistors on the neck board of the tube, one per RGB channel, so a failed unit typically wipes out just one colour.

Q: Can I swap transistors on the neck board to diagnose the fault?
A: Yes, swapping two of the RGB output transistors is a standard diagnostic trick - if the missing colour moves to a different channel, the transistor is confirmed faulty.

Notes

Legacy/NOS part mainly stocked for repair of vintage (1990s-2000s) CRT televisions and monitors; not intended for new designs.

Note: Price refers to one (1) piece. The component is shipped in bulk without individual packaging.

Transistor Type: BJT (Bipolar Junction Transistor)
Transistor Polarity / Channel: NPN
Transistor Case Style: TO-202

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