2N3055 Transistors.

[Ed_Dinning]

Hi Gents, we used some Westinghouse types back in the 70's and a variety of part numbers. They all had really chunky cases so presumably a good thermal transient response. Certainly the biggest cases I'd seen on commercial types.

Ed

[kalee20]

Originally Posted by Boulevardier

Refugee, thanks. You mean 500mA emitter current? And base dc bias - about 20mA? Ensure consistent input signal voltage...

Surely you want consistent input CURRENT, so have plenty of signal voltage but stick a resistor in series. Maybe 10V and 1k.

The fT is defined for current gain. Squirting a constant voltage in, will I understand, give a reasonably constant output - but the input impedance will drop as the current gain falls. But with constant input voltage, you wouldn't know this bit.

I'm not someone who pushes transistors to their frequency limits, so anyone with better knowledge, correct me!

[Radio Wrangler]

I've sawn round the lids of suspect 2N3055 and a few known good reference ones and lived to tell the tale. The die is soldered down onto a copper heat spreader onto the flange (in a good one)

Really shonky fakes have tiny die and few bond wires on the emitter

Good ones of different makes and vintages can look quite different. I've never opened an early one, though. Large die and heat spreaders are usual on real ones. and multiple emitter bonds.

Not quite good enough wafers of fancy high performance SMPS devices and RF devices often meet the 2N3055 minimum requirements, so sticking them in a TO3 can and writing 2N3055 on it is a way of recouping some of the value of what would otherwise be filling holes in roads. So a big die is no guarantee of a nice tame beast.

I deal regularly with devices that have heatsink faces not connected to collector or drain, and most probably have beryllia inside. I don't open those!

David

[Maarten]

Originally Posted by Ambientnoise

I emphasise the warning above. Although the chances are that there is no BeO in these (tends to be more in RF and/or isolated case devices), it is not worth the risk.

I would estimate the chances of a 2N3055 containing BeO, well below zero. It would have been prohibitively elaborate and expensive to use in devices that don't require its use and a 2N3055 is by no means sufficiently high-tech for that. Also, some kind of warning is usually present.

Testing for fT could be done with a sine generator and a scope by turning up the frequency and observing the amplitude drop in the output signal.

[Boulevardier]

The original Quad thread discussing problem of higher fT in newer 2N3055s is now closed, so just a further thought here. I have two pairs of BDY20 already mounted on heatsinks and ready to use. Looking at brief specs, they seem to be a close match for 2N3055, and have have an fT of just 1MHz - very similar to those original 2N3055s. This would make them look like a good replacement in the Quad 33 circuit to avoid the instability problem of later 2N3055s. Am I right?

[Ted Kendall]

Could be worth a try - the main point is that the power device has to be the slowest of the triple, and if the other parameters match, it should work.