Something interesting happened when I contacted ONSEMI. They emailed back and listed this: http://www.onsemi.com/pub_link/Collateral/2N3055-D.PDF as an exact replacement. It says 15A & 115 watt? Is that RMS wattage or referring to something else like power consumption?
Then, they listed this: http://www.onsemi.com/pub_link/Collateral/2N5883-D.PDF as (similar transistor with better features). It's rated at 25A and states 200 watt? Would that be compatible? Or would a serious overhaul with transformer, resistors, heat sink (obviously) etc. need to occur before something like that could even be used?
Then, they listed this: http://www.onsemi.com/pub_link/Collateral/2N5883-D.PDF as (similar transistor with better features). It's rated at 25A and states 200 watt? Would that be compatible? Or would a serious overhaul with transformer, resistors, heat sink (obviously) etc. need to occur before something like that could even be used?
The OnSemi parts are modern versions of the device, but as I mentioned before, they are made using different methods and processes compared to back in the day when your amp was made.
Look at the fT or 'gain bandwidth product' figure of 2.5MHz. Your original devices could only dream of that and will be closer to 0.2MHz.
So replacing old with modern could throw up some very real problems with stability and oscillation because your amp may rely in part on those very characteristic to help define its stability margins.
The 2N5883 is faster again at around fT 4MHz.
The 15A is the maximum current the device will stand. The 115 watt is the maximum power the device can dissipate. There is also a maximum voltage in there as well of 60 volts I think for the 2N3055. So if the device has 40 volts across it then it can only pass 2.8 amps before it exceeds its power rating (because watts = amps * volts). Things get even more complicated because at the higher voltages the device becomes more prone to fail even at currents that seem within spec. Now the maximum rating is bounded by a curve called S.O.A.R. or safe operating area.
Safe operating area - Wikipedia, the free encyclopedia
Look at the fT or 'gain bandwidth product' figure of 2.5MHz. Your original devices could only dream of that and will be closer to 0.2MHz.
So replacing old with modern could throw up some very real problems with stability and oscillation because your amp may rely in part on those very characteristic to help define its stability margins.
The 2N5883 is faster again at around fT 4MHz.
The 15A is the maximum current the device will stand. The 115 watt is the maximum power the device can dissipate. There is also a maximum voltage in there as well of 60 volts I think for the 2N3055. So if the device has 40 volts across it then it can only pass 2.8 amps before it exceeds its power rating (because watts = amps * volts). Things get even more complicated because at the higher voltages the device becomes more prone to fail even at currents that seem within spec. Now the maximum rating is bounded by a curve called S.O.A.R. or safe operating area.
Safe operating area - Wikipedia, the free encyclopedia
This matches the usual usage of these symbols.
G = Ground = Zero Volts.
B = supply voltage
B+ = +ve supply voltage, also labeled Vcc
B- = -ve supply voltage, also labeled Vee and sometimes Vdd
Can you elaborate on the ft and what it means in the practical world? Is that some speed the device operates at? i.e. how quickly it can respond or something?
That software program you mentioned earlier, could I theoretically recreate the amp board section of this amplifier with it, then see what introducing changes would do? This is probably one of the least elaborate home stereo amp boards I have, so I think it'd be the easiest to work with as far duplicating goes. Suppose ultimate goal would be to have a better understanding of amplifier circuits, how they work, and how to possibly improve them or work on them with a solid grasp of what's going on.
In practice, have any of you found modern higher-end resistors with tighter tolerances improve clarity or overall sound when dealing with the amp board only? When I swapped out the 2 polyester caps on amp board for Vishay metalized polypropylene (after all the electrolytic caps had been replaced) for example, I noticed a fairly significant improvement with sound overall, most notably with a cleaner sounding high freq. that seemed to have less ghosting or rather when a cymbal crashed, it sounded more solid and precise for example, w/o sounding as distorted. Also noticed bass cleaned up and sounded less "boomy" and seemed tighter, more accurate. Was wondering if resistors can further improve upon that? And resistors at the end of their 20% tolerances, can have a huge negative impact on sound quality overall?
I'm surprised they'd recommend those as a replacements (w/o a disclaimer) if the specs are that different. Also surprised the newer 3055's are miles ahead of the old ones yet being offered as direct replacements?
Sorry for the million questions. I find it easier to understand in context this way vs. reading a ton of material that has everything lumped together w/o knowing how it's applied. Thanks for the patience everyone!
Very helpful, thank you. Wish I had a schematic to which to reference these values against. The +ve is what the emitter lead of the transistor should see? and -ve is what the base lead sees? Am I understanding that correctly?
Suppose if I took these readings with a working unit, jotted them down somewhere, they could possibly help troubleshoot it in the future?
An EF stage has the Emitter connected to the Output.
The Base receives the control signal.
The Collector is connected to the supply.
Go back and look at posts29, 31 & 34.
An Emitter Follower is also called a Common Collector. This is one of the THREE ways that a BJT can be connected as an amplifier.
The other two are Common Base and Common Emitter.
The Common X tells you which lead is connected to both the input side and the output side.
Common Collector (EF) has the Collector connected to both the Input (control) and to the Output via the zero impedance of the PSU. Look at post34
The Base receives the control signal.
The Collector is connected to the supply.
Go back and look at posts29, 31 & 34.
An Emitter Follower is also called a Common Collector. This is one of the THREE ways that a BJT can be connected as an amplifier.
The other two are Common Base and Common Emitter.
The Common X tells you which lead is connected to both the input side and the output side.
Common Collector (EF) has the Collector connected to both the Input (control) and to the Output via the zero impedance of the PSU. Look at post34
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In very simple terms its a measure of the frequency where the current gain of the device falls to 1.
Up to a point yes. If you have the circuit diagram then you can simulate it. The problem with simulation is finding or creating transistor models that reflect the real devices used but yes, you can.
🙂 Welcome to the world of 'experimenter expectation'. The real test is whether you can identify a difference 'blind' without knowing which is which,
Resistor tolerance shouldn't impact to much on performance. Are you sure they are 20% parts fitted, 5% would be more usual for all the small values. The large emitter resistors could be 20% but that wouldn't matter.
Its not their fault really, they have no idea what you are using them for. For many applications they would be guaranteed fine, older amplifiers where device characteristic might have played a part in the basic design, less so.
An EF2 with a Miller-compenated front end is perfectly stable with output devices having a very wide range of fT. That's the whole idea behind uning those two techniques together - overall Nyquist stability is pretty much independent of the output device characteristics. With extremely fast (>30 MHz) or extremely slow (<1 MHz) devices, localized oscillations can occur. But they can be treated independently from the overall loop compensation - cross that bridge when and if you come to it. How old are the outputs? There is probably a date code on there somewhere. Only really old ones, and some brands are the old 0.2 MHz units. Most made after 1978 will be 'normal' ones that are like the ones On/Motorola are selling now. Usually, if PNPs are used at all, you have the 2.5MHz epitaxials - as the other types are NOT available in PNP. There are exceptions, the most notable being an old NAD that didn't use emitter resistors. That's the other giveaway as to what you probably have.
If you did upgrade to the 5883's, it probably wouldn't change anything. Might have less distortion driving 4 ohm loads, but such use would still be limited by the heat sinking. With such a small heat sink, the difference between a 115W transistor and a 200W is negligible. They will still operate at the same die temperature for all practical purposes. The higher beta at 10-15A is the only thing you could notice.
If you did upgrade to the 5883's, it probably wouldn't change anything. Might have less distortion driving 4 ohm loads, but such use would still be limited by the heat sinking. With such a small heat sink, the difference between a 115W transistor and a 200W is negligible. They will still operate at the same die temperature for all practical purposes. The higher beta at 10-15A is the only thing you could notice.
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