I'm helping a friend resurrect an Ampex 440 studio tape deck, and a problem popped up.
After running nicely for hours, one playback channel suddenly got noisy. The prime suspect is the first transistor in the signal chain, a 2N4104. In today's world, what would be a good sub for this "low noise" transistor? The specs:
NPN, non-Darlington
Small PTH package; TO-18, TO-92, etc.
Vce - 60 V minimum
Ic - 50 mA minimum
Gain - 100 minimum
Thanks.
ak
After running nicely for hours, one playback channel suddenly got noisy. The prime suspect is the first transistor in the signal chain, a 2N4104. In today's world, what would be a good sub for this "low noise" transistor? The specs:
NPN, non-Darlington
Small PTH package; TO-18, TO-92, etc.
Vce - 60 V minimum
Ic - 50 mA minimum
Gain - 100 minimum
Thanks.
ak
The current gain is specified as at least 1400 at 1 mA on the Mouser and Digi-Key sites. They still have it, but only sell them in multiples of 2000 units.
Those specs are data sheet values.
You should also look at how it is used in the actual circuit and what parameters actually matter. For example if the front end runs on say 20 volts DC then you don't actually need a 60 volt rated part. Same for IC. Look how much collector current can actually flow under normal conditions.
Doing that can open up a whole new group of parts that might be suitable.
You should also look at how it is used in the actual circuit and what parameters actually matter. For example if the front end runs on say 20 volts DC then you don't actually need a 60 volt rated part. Same for IC. Look how much collector current can actually flow under normal conditions.
Doing that can open up a whole new group of parts that might be suitable.
My small signal, low noise, high beta NPN of choice is the MPSA18, current and widely available. Vceo max is 45 V but, as Mooly said above, this may be fine in your circuit.
I thought there might be something in the MPS or MPA lines. Thanks.
Power for the signal system is +39 Vdc, but the preamp stage has much less than that because of some power rail R-C filtering before its collector load. Working on a module extender to get some actual readings.
ak
Power for the signal system is +39 Vdc, but the preamp stage has much less than that because of some power rail R-C filtering before its collector load. Working on a module extender to get some actual readings.
ak