Modern NPN to replace 2N2484 as a buffer transistor?

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

777funk

Well-known member
Joined
May 7, 2009
Messages
156
Looks like the 2N2484 that's in the buffer(?) section in my Acoustic 370 has the following characteristics:
MAXIMUM RATINGS:
Collector-Base Voltage VCBO 60 V
Collector-Emitter Voltage VCEO 60 V
Emitter-Base Voltage VEBO 6.0 V
Continuous Collector Current IC 50 mA

ICBO VCB=45V 10 nA
ICBO VCB=45V, TA=150°C 10 μA
ICEO VCE=5.0V 2.0 nA
IEBO VEB=5.0V 10 nA
BVCBO IC=10μA 60 V
BVCEO IC=10mA 60 V
BVEBO IE=10μA 6.0 V
VCE(SAT) IC=1.0mA, IB=100μA 0.35 V
VBE(ON) VCE=5.0V, IC=100μA 0.5 0.7 V
hFE VCE=5.0V, IC=1.0μA 30
hFE VCE=5.0V, IC=10μA 100 500
hFE VCE=5.0V, IC=10μA, TA=-55°C 20
hFE VCE=5.0V, IC=100μA 175
hFE VCE=5.0V, IC=500μA 200
hFE VCE=5.0V, IC=1.0mA 250
hFE VCE=5.0V, IC=10mA 800

hfe VCE=5.0V, IC=1.0mA, f=1.0kHz 150 to 900
fT VCE=5.0V, IC=50μA, f=5.0MHz 15 MHz

and the transistor that was in there (replaced with a 2N3391A by a tech before I owned the amp) was about half of the voltage ratings (25V Vce). All was working fine until I had a slip with a testing wire and shorted the output of the preamp to mains. I only have a 30Vce transistor on hand. Looking at the circuit, the B+ is 32V on the preamp and the transistor is in circuit with resistors, so I think it shouldn't see the full 32V. Also, the tech's replacment was only 25V and seemed to have done fine.

The 2N5088BU I installed has these characteristics:
Collector-Base Voltage VCBO 35 V (25v less than orig)
Collector-Emitter Voltage VCEO 30 V (30v less than orig)
Emitter-Base Voltage VEBO 4.5 V (1.5v less than orig)
Continuous Collector Current IC 100 mA (50mA more than orig)
hfe VCE=5.0V, IC=1.0mA, f=1.0kHz 350 to 1400 (higher than orig)
fT = 50MHz

I installed it and it's working well so far and sounds very good to my ears.

BUT is it an ok fit? Would there be a better common BJT that could be used?
 

Attachments

  • Acoustic-370-manual-410056_PWR_AMP_IN_MOD_and_replacement_transistor.pdf
    603.8 KB · Views: 0
Last edited:
Top