BC 456
Polarity: PNP
Maximum Collector Power Dissipation: 0.3 W
Maximum Collector-Base Voltage: 30 V
Maximum Collector-Emitter Voltage: 30 V
Maximum Emitter-Base Voltage: 5 V
Maximum Collector Current: 0.1 A
Maximum Operating Junction Temperature: 125 °C
Transition Frequency: 150 MHz
Forward Current Transfer Ratio (hFE Value): 125
Collector Capacitance: 6 pF
Package: TO92
In bold you have the properties of the replacement, if they're different :
2SA2029 :
https://www.digikey.com/en/products/detail/onsemi/2SA2029M3T5G/1475407NS2029 :
https://www.digikey.com/en/products/detail/onsemi/NS2029M3T5G/1792901Polarity: PNP
Maximum Collector Power Dissipation: 0.30 W
0.265WMaximum Collector-Base Voltage: 30 V
60vMaximum Collector-Emitter Voltage: 30 V
50vMaximum Emitter-Base Voltage: 5 V
6vMaximum Collector Current: 0.1 A
Maximum Operating Junction Temperature: 125 °C
150cTransition Frequency: 150 MHz
140 MhzForward Current Transfer Ratio (hFE Value): 125
min. 120, max 560Collector Capacitance: 6 pF
3.5pFPackage: TO92
SOT-23They're general purpose pnp transistors, they're unlikely to be used at close to their maximum specifications.
Maybe this would also work, just has lower collector emitter voltage.
MMS8550 :
https://www.digikey.com/en/products/detail/onsemi/2SA2029M3T5G/1475407Polarity: PNP
Maximum Collector Power Dissipation: 0.30 W
0.30WMaximum Collector-Base Voltage: 30 V
40vMaximum Collector-Emitter Voltage: 30 V
25vMaximum Emitter-Base Voltage: 5 V
5vMaximum Collector Current: 0.1 A
0.5AMaximum Operating Junction Temperature: 125 °C
150cTransition Frequency: 150 MHz
Forward Current Transfer Ratio (hFE Value): 125
min. 120, max 350Collector Capacitance: 6 pF
?Package: TO92
SOT-23higher voltage ...
BC806 :
https://www.digikey.com/en/products/detail/nexperia-usa-inc/BC806-16VL/10496455Polarity: PNP
Maximum Collector Power Dissipation: 0.30 W
0.25W - 0.345W if big enough padMaximum Collector-Base Voltage: 30 V
80vMaximum Collector-Emitter Voltage: 30 V
80vMaximum Emitter-Base Voltage: 5 V
8vMaximum Collector Current: 0.1 A
0.5AMaximum Operating Junction Temperature: 125 °C
150cTransition Frequency: 150 MHz
Forward Current Transfer Ratio (hFE Value): 125
min. 100, max 250 for -16 version, 160 - 400 for -25 version Collector Capacitance: 6 pF
5 pFPackage: TO92
SOT-23