so can you recommend me a good and cheap transistor that i can use? i don't know what to choose.
adi81bv said:
Difficult to say without the silkscreen. If you're having difficulties building the amp, I would buy Rod's PCBs, then at least you know that that part is good.
romania is not a good country to buy stuff online. they will tax u at the customs that u will not buy anything else after. it happened to some friends.
Thank you very much. that is a nice amp and i like the ideea 🙂. I will assamble the p3a tomorrow because i have the parts, but after that or if i have problems i will read the pages from that thread. seems a good job. Thank you again. I will also point it out to my friend.
I think i found the problem with the amp. Transistor BD250C has the following impedance B-C = 567 and B-E = 566, BUT when I measured the resistance across C-E it was in both ways 0.8ohm (the minimum that my milliampere-meter can measure).
So I think this is the fault with the amp. I will change it and power it up to see if this was the problem. First I will measure also the other transistors.
So I think this is the fault with the amp. I will change it and power it up to see if this was the problem. First I will measure also the other transistors.
Hi adi81bv,
By George, I think you've got it man! You have found a rather common fancy looking wire.
-Chris
By George, I think you've got it man! You have found a rather common fancy looking wire.
-Chris
Hi.
I replaced the BD250C... but everything went on fire. Probably other components were damaged and thats why it burned.
(this time both the power transistors are damaged, and also some resistors). In conclusion, there is no point trying to repair this one, maybe just recover the pcb board.
____________________________
Now I have almost all the parts for a new amp. I also added some pictures of the parts that i will use.
Power transistors Motorola MJ15003 and ON MJ15004. (They are in steel case, the epoxy around the legs is 5mm in diameter and the paint is wearing off hard - not very hard 🙂 - with acetone). Hope that they are genuine transistors.
I will use BC546A, as Rod suggested in his original scheme. Do I have to match all 4 transistors for hFE?(help)
For drivers i will use BD139/BD140. These should be also mached for hFE?(help)
The resistors are all minimum 1/2W and 10R,3k3 - are 1W and 0R33 are 5W.
About the capacitors I am not very sure what to use.
For input cap i should choose between 4,7u (the big red one) and a 4,7uF/50V Jamicon electrolytic one.
The shunt capacitor - C2 = 220p - I have 2 options: ceramic or tantalum??? (the blue one) - Are they OK??? (help)
The Zobel C7 and supply bypass C+&C- = 100n. Are the yellow capacitor OK??? And one more question> .1J100 are 100n/100V???(help)
The input coupling cap - C6? - and the miller - C4 - (=100pf) capacitors i only have ceramics (the small 101 marking caps) Can I use the green one instead??? (2A102J = 0,001uF i suppose) (help)
For the moment I am working to the layout of the board and I wait for your help regarding the components that i should use.
Thank you very much for your help.
Pictures:
I replaced the BD250C... but everything went on fire. Probably other components were damaged and thats why it burned.
(this time both the power transistors are damaged, and also some resistors). In conclusion, there is no point trying to repair this one, maybe just recover the pcb board.____________________________
Now I have almost all the parts for a new amp. I also added some pictures of the parts that i will use.
Power transistors Motorola MJ15003 and ON MJ15004. (They are in steel case, the epoxy around the legs is 5mm in diameter and the paint is wearing off hard - not very hard 🙂 - with acetone). Hope that they are genuine transistors.
I will use BC546A, as Rod suggested in his original scheme. Do I have to match all 4 transistors for hFE?(help)
For drivers i will use BD139/BD140. These should be also mached for hFE?(help)
The resistors are all minimum 1/2W and 10R,3k3 - are 1W and 0R33 are 5W.
About the capacitors I am not very sure what to use.
For input cap i should choose between 4,7u (the big red one) and a 4,7uF/50V Jamicon electrolytic one.
The shunt capacitor - C2 = 220p - I have 2 options: ceramic or tantalum??? (the blue one) - Are they OK??? (help)
The Zobel C7 and supply bypass C+&C- = 100n. Are the yellow capacitor OK??? And one more question> .1J100 are 100n/100V???(help)
The input coupling cap - C6? - and the miller - C4 - (=100pf) capacitors i only have ceramics (the small 101 marking caps) Can I use the green one instead??? (2A102J = 0,001uF i suppose) (help)
For the moment I am working to the layout of the board and I wait for your help regarding the components that i should use.
Thank you very much for your help.
Pictures:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Hi,
from post 20
R5 passes between 1.5mA and 2.5mA.
Have you contacted Bob Ellis to buy some BC546c and BC556c yet?
You will need to measure the voltage across LED1 correctly. Your diagram shows 2.5V, this cannot be right for an ordinary LED.
Let's assume 2mA at the moment then each half of the LTP passes 1mA. That is the test current that must flow to check the Vbe and the hFE. Be careful checking Vbe and monitoring the base current, the DMM resistance will change the apparent impedance/voltage at the base and distort your answer. A 10M input resistance on your meter will help reduce the error
The drivers do not have to be matched. But some builders says performance is improved if you do so. This time match for hFE at operational current.
That blue one is not Tantalum.
Tantalum is polarised and low voltage. That is a high voltage ceramic disc with a HiK dielectric, not good for audio.
from post 20
yes, the input transistors should be matched. You must arrange for the correct current to flow while doing the test.
R5 passes between 1.5mA and 2.5mA.
Have you contacted Bob Ellis to buy some BC546c and BC556c yet?
You will need to measure the voltage across LED1 correctly. Your diagram shows 2.5V, this cannot be right for an ordinary LED.
Let's assume 2mA at the moment then each half of the LTP passes 1mA. That is the test current that must flow to check the Vbe and the hFE. Be careful checking Vbe and monitoring the base current, the DMM resistance will change the apparent impedance/voltage at the base and distort your answer. A 10M input resistance on your meter will help reduce the error
The drivers do not have to be matched. But some builders says performance is improved if you do so. This time match for hFE at operational current.
That blue one is not Tantalum.
Tantalum is polarised and low voltage. That is a high voltage ceramic disc with a HiK dielectric, not good for audio.
for the 220p, C2 can I use ceramic??? in my home town there is now other type of capacitor. 😡 for these value, nor something close 50p-100n
AndrewT said:
that is actually what rod recommends. because with the lower voltage ceramics (50V) the operating voltage is a large percentage of the voltage rating of the cap so capacitance varies wildly. with a 2kV cap, the operating voltage is only a very small percentage of the voltage rating of the cap so capacitance should only vary by a very small amount.
So, a capacitor with voltage ratings of 2kV like the blue one that i have is a good choice for C2? in a P3a amp?
adi81bv said:
actually, it would be better choice if you got those 2KV units for the 100pF caps. the 220pF cap only sees less than a couple of volts so a 50V unit would work perfectly fine here.
So it would be perfect to have a cap that is rated in kV, but what about the type of cap. A ceramic cap will do the job right? Or should i search for other type?
Hi,
search for polypropylene in values above 100pF.
For lower values only silvered mica and polystyrene are any good for audio. I have not been able to find low value PP here in the UK.
All the ceramic vary capacitance with voltage changes. The HiK version worse than the low K versions.
search for polypropylene in values above 100pF.
For lower values only silvered mica and polystyrene are any good for audio. I have not been able to find low value PP here in the UK.
All the ceramic vary capacitance with voltage changes. The HiK version worse than the low K versions.
the best to use are polystyrene caps but they easily get damaged with soldering.
next best thing is the 2kV caps for the 100pF caps. on the 200pF ones, 50V is ok but the 2kV won't hurt to use.
next best thing is the 2kV caps for the 100pF caps. on the 200pF ones, 50V is ok but the 2kV won't hurt to use.
I found home 2 caps 0.1nF/63V (they seem to be mkp type). For 220p i will use the ceramic 2kV - i don't have any alternative so.... hope that will be good.
I assembled part of the circuit. Pictures:
I assembled part of the circuit. Pictures:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
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