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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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18th Sep 2017, 8:18 pm | #21 |
Dekatron
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,194
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Re: 2N3055 Transistors.
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 |
18th Sep 2017, 9:14 pm | #22 | |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,079
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Re: 2N3055 Transistors.
Quote:
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! |
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18th Sep 2017, 11:04 pm | #23 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,864
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Re: 2N3055 Transistors.
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
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20th Sep 2017, 10:48 pm | #24 | |
Dekatron
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,199
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Re: 2N3055 Transistors.
Quote:
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. Last edited by Maarten; 20th Sep 2017 at 10:54 pm. |
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21st Oct 2017, 1:40 pm | #25 |
Octode
Join Date: Sep 2017
Location: Bristol, UK.
Posts: 1,654
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Re: 2N3055 Transistors.
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?
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21st Oct 2017, 3:31 pm | #26 |
Dekatron
Join Date: Jul 2008
Location: Kington, Herefordshire, UK.
Posts: 3,670
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Re: 2N3055 Transistors.
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.
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