First of all hello to everyone and this is my 1st post here. I feel really dumb here and way out of my league with the knowledge that most of you guys have. But I have been staring at data sheets till I'm crossed eyed and have just one question. I'm replacing a BC212 transistor and of course they are obsolete. I did some scouting on the internet and found a recommendation of using a BC556 as a substitute. I have an order with Mouser Electronics and this is the last item I need. What they have in stock there is a BC556ABU. Is there much difference and will it work in place of the BC212? Any comments would be appreciated and thanks in advance.
BC212 Transistor Question (Marshall amplifier repair)
- Thread starter sweatyk
- Start date
The BC 556 might work, both are pnp and the 556 has a higher voltage and power rating but it depends upon the application.
Both transistors come in a variety of pinouts depending upon end letter so you need to ensure a match.
The BC 212 has a current rating of 200mA and a frequency Ft of 200 MHz, whereas the 556 has a currrent rating of only 100mA and and Ft of 150 MHz so you need to check the application here.
Both transistors come in a variety of pinouts depending upon end letter so you need to ensure a match.
The BC 212 has a current rating of 200mA and a frequency Ft of 200 MHz, whereas the 556 has a currrent rating of only 100mA and and Ft of 150 MHz so you need to check the application here.
Just have a look at this.
http://alltransistors.com/crsearch....5&ic=0.2&tj=150&ft=200&cc=9&hfe=60&caps=TO226
You have a lot more choices.
Ramesh
http://alltransistors.com/crsearch....5&ic=0.2&tj=150&ft=200&cc=9&hfe=60&caps=TO226
You have a lot more choices.
Ramesh
Ras thanks for that link. I will save it for future reference. This is part of the output circuit on a solid state guitar amp (Marshall Valvestate) that I messed up on. It worked prior to this with the exception of the reverb. I was checking the output voltage on the IC that controls it when my hand twitched and shorted the output transistors. Given the age of the amp and the usage it has had I have decided to replace the transistors and diodes that were affected in this circuit. Most of which is available at Mouser except the BC212 and also the BC182 that I need. They did not read short but as a precaution I feel that changing them would be better so that I don't have to go back in it at a later date.
Studiot I live in the US on the east coast in sunny Florida. If you had a couple of the BC212's and the BC182's I would like to see how much you would charge plus the shipping.
Another question is looking at the data sheet for transistors what does the Hfe mean? When looking for a replacement or equivalent how important is that number?
Studiot I live in the US on the east coast in sunny Florida. If you had a couple of the BC212's and the BC182's I would like to see how much you would charge plus the shipping.
Another question is looking at the data sheet for transistors what does the Hfe mean? When looking for a replacement or equivalent how important is that number?
You are welcome to a couple of each for the postage (they were European/UK types). They will go in a small envelope.
But you need to determine pinout since they were produced in several configurations.
The common ones are shown below. The 212 and 182 were complementary.
The current gain Hfe (also called beta, β) is not likely to be relevant (ie adequate) as they were a good modern transistor.
I can tell you the measured value of any I send if you wish.
PM me.
But you need to determine pinout since they were produced in several configurations.
The common ones are shown below. The 212 and 182 were complementary.
The current gain Hfe (also called beta, β) is not likely to be relevant (ie adequate) as they were a good modern transistor.
I can tell you the measured value of any I send if you wish.
PM me.
Attachments
Hello,
Here I have a zip-file with the data of a lot of transistors:
transistor_tabel.xls.zip
Unpacked you will find a excel sheet that you can search.
Bertus
Here I have a zip-file with the data of a lot of transistors:
transistor_tabel.xls.zip
Unpacked you will find a excel sheet that you can search.
Bertus
Being new to this sight I wasn't sure..........well there's my 10th post!!!!!!!
OK, I have found a few BC212A which are the same pinout as the BC 212. So that is OK
Needless to say I have dozens of the alternative BC212L type.
The BC182 are more problematic as I have none for that pinout. They are all BC182L.
Now I have plenty of both types of BC214C and BC183C which are part of the same series, but better transistors. In particular they are higher gain, lower noise types.
The only thing is that they have a lower theorectical guaranteed breakdown voltage of 30 volts instead of 45.
My BC212 measures 96 volts at breakdown.
I have measured some and the actual breakdown voltage is 55-60 for the BC214 and 75 volts for the BC183.
Again I have plenty of the L variety.
Looking at the Marshall it has ±12 volt rails and ±45 volt rails, if it is the model I think.
So the other transistors may be fine as they will not see the full rail.
What do you think and what circuit information do you have?
Needless to say I have dozens of the alternative BC212L type.
The BC182 are more problematic as I have none for that pinout. They are all BC182L.
Now I have plenty of both types of BC214C and BC183C which are part of the same series, but better transistors. In particular they are higher gain, lower noise types.
The only thing is that they have a lower theorectical guaranteed breakdown voltage of 30 volts instead of 45.
My BC212 measures 96 volts at breakdown.
I have measured some and the actual breakdown voltage is 55-60 for the BC214 and 75 volts for the BC183.
Again I have plenty of the L variety.
Looking at the Marshall it has ±12 volt rails and ±45 volt rails, if it is the model I think.
So the other transistors may be fine as they will not see the full rail.
What do you think and what circuit information do you have?
Studiot
It is a model 8080. The transistors are TR11 and TR12. I am attaching the schematic. Being you have way more knowledge with this I will trust your judgement. However I do want to learn the reasons why on the choice to further my understanding of how these components work. Let me know what you think. Thanks again!
It is a model 8080. The transistors are TR11 and TR12. I am attaching the schematic. Being you have way more knowledge with this I will trust your judgement. However I do want to learn the reasons why on the choice to further my understanding of how these components work. Let me know what you think. Thanks again!
First let me say that I have never worked on this particular model, so anyone with personal knowledge is welcome to chip in (pun intended) here.
That is what makes AAC special - The high level of cooperation between members.
Now did you say you are refurbishing this amp?
The transistors in question are not actually necessary for the operation it should work perfectly without them.
They form (part of) the protection circuit so if you are refurbishing you can remove them to get the main parts working properly. so long as you don't overdrive things.
They work by monitoring the output darlington emitter currents across the emitter resistors, R118 and R96. They only turn on when there is sufficient current through these resistors to provide base bias and drive. They work by then shunting some of the darlington base drive signal to earth in overdrive conditions.
Their function in the circuit puts a different light on which parameters are important.
They will never see a greater voltage than the BE pedestal voltage if their respective darlington, TR8 or TR10 which will be somewhere between 1.5 and 3 volts I guess.
So voltage rating is not an issue.
Current rating may be another matter and why Marshall went for a 200mA transistor rather than the more usual 100mA small signal job, so we should stick with that.
Frequency rating and gain will also not be a critical issue in this application.
However the resistor pairs R117/R116 and R115/R97 will have been chosen in relation to the Vbe characteristics of the BC212 and BC182 so this characteristic is important in any substitution.
How is the rest of the refurb going?
That only leaves the issue of pinout to resolve.
So please check if the centre terminal of TR12 is connected to the junction of R117 and R116 and not D5 or earth, and similarly the centre wire of TR11 to the junction of R115 and R97.
Edit a rethink on the voltage ratings
The output followers will have a voltage gain of about 1 so the earlier voltage amp stages of the power amp will need to swing the bases of the darlingtons, depending upon the load
For 8 ohms the peak required is about 40 volts for 100 watts and 35 for 80watts
For 4 ohms the peak is 28 and 25 volts
For 2 ohms it is 20 volts and 18 volts
That is what makes AAC special - The high level of cooperation between members.
Now did you say you are refurbishing this amp?
The transistors in question are not actually necessary for the operation it should work perfectly without them.
They form (part of) the protection circuit so if you are refurbishing you can remove them to get the main parts working properly. so long as you don't overdrive things.
They work by monitoring the output darlington emitter currents across the emitter resistors, R118 and R96. They only turn on when there is sufficient current through these resistors to provide base bias and drive. They work by then shunting some of the darlington base drive signal to earth in overdrive conditions.
Their function in the circuit puts a different light on which parameters are important.
They will never see a greater voltage than the BE pedestal voltage if their respective darlington, TR8 or TR10 which will be somewhere between 1.5 and 3 volts I guess.
So voltage rating is not an issue.
Current rating may be another matter and why Marshall went for a 200mA transistor rather than the more usual 100mA small signal job, so we should stick with that.
Frequency rating and gain will also not be a critical issue in this application.
However the resistor pairs R117/R116 and R115/R97 will have been chosen in relation to the Vbe characteristics of the BC212 and BC182 so this characteristic is important in any substitution.
How is the rest of the refurb going?
That only leaves the issue of pinout to resolve.
So please check if the centre terminal of TR12 is connected to the junction of R117 and R116 and not D5 or earth, and similarly the centre wire of TR11 to the junction of R115 and R97.
Edit a rethink on the voltage ratings
The output followers will have a voltage gain of about 1 so the earlier voltage amp stages of the power amp will need to swing the bases of the darlingtons, depending upon the load
For 8 ohms the peak required is about 40 volts for 100 watts and 35 for 80watts
For 4 ohms the peak is 28 and 25 volts
For 2 ohms it is 20 volts and 18 volts
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