pros and cons of using 2sc5200 1943 Toshiba Transistors in Class A

[rhythmsandy]

I have a 300W in 8 ohm 2sc5200 1943 amplifier which Im driving with lme49810 and psu ratings of +/-53 DC now I want to bias this amp in class A

I have 2SC1517 as biasing transistor how many amps I can bias?

It has 5 pairs of output transistors 5200 1943 pair

I have few questions can I bias this amp in class A? what are the pros and cons?

I have IGBT heatsinks which are pretty huge I there anything that I need to consider while biasing this amp in class A? or I shouldnt bias this amp in class A

 

[FoMoCo]

I think you'd have to reduce the supply voltage by quite a bit to get true class A. To fully utilize your supply rails with an 8 ohm resistive load you'd need at least 6.625 amps not to leave class A until clipping. This is a static dissipation of ~700W for the upper and lower half combined. But... A speaker isn't resistive. You'll need more than 6.625 amps, probably closer to 10. Now you're looking at a static dissipation of a kilowatt.

The short answer to your question: Don't bias it in class A. If you really need class A, buy one. But, you won't get 300W. There's a reason why class A amplifiers are not extremely high power.

 

[rhythmsandy]

I am very clear that its not possible to get 300W of class A with this amp but

I understand one thing that using +/-40v is sufficient to run the amp in class A.

6.625Amps of Bias?

I am happy even if im getting 50W of class A out of this config but i just wanted to know that are these transistors safe enough to bias in class A?

I understand using mosfets work in negative temp coef but what if we have big heatsinks for transistor based class A..

 

[rhythmsandy]

I have a 300W in 8 ohm 2sc5200 1943 amplifier which Im driving with lme49810 and psu ratings of +/-53 DC

sorry my correction im using +/-78V for 300W in 8 ohms

i have another version with lm4702 with +/-53DC both the amps are driven in class AB now...

 

[moschfet]

If you want to drive your module in class-A, you have to change so many values, that it is equivalent with an new construction of a amplifier. And nearly as expensive.

But I estimate you can't design an amp from beginning, otherwise you would not ask such questions

My advise, try to copy one of the Pass-amps. Which are well known and have been copied thousands of times.

 

[FoMoCo]

6.625Amps of Bias?

To get maximum power into an 8 ohm resistive load, you need the bias to be the supply voltage divided by 8. Any less current (and it should be less) and you need to lower the supply voltage to match. Otherwise you just generate more heat than needed.

All this goes out the window if you allow class AB, though. If AB is okay... Just leave it alone.

I still think the best idea is to just leave it alone is the best option.

 

[rhythmsandy]

i want to try 1.5A bias i would be using supply at +/-35 Im just asking is there any harm or burning of the amp possibility...

 

[Ian Finch]

The sums are still wrong - 1.5 amps bias, even in a push-pull class A design with an EF output stage, only permits about 28W/8R.
The rail voltages then have to be lowered to around 27V also. It becomes obvious that much of the original amplifier design is now redundant and a redesign of the bias controller is necessary.

It has already been said that the class AB amp is best left as is - If you want to try class A, start with a known, inexpensive design rather than be disappointed with a hobbled class AB design that still needs someone else to redesign for you. I suspect it will be cheaper starting with smaller proven design, given the radical changes required to the larger amplifier.

Bear in mind that the largest cost of any amplifier is the transformer, heatsinks and case. If you need to change these, the difference to a new amplifier is not so great.

 

[east electronics]

I agree with Ian
plus that for a real hi end amplifier ( if it can be called like that cause its biased in class A) there is also other things that are critical for the rest of the design and given that the duty between the two topologies /technologies that you are trying to mix match are totally different

I will say no to that ...big time

 

[rhythmsandy]

The sums are still wrong - 1.5 amps bias, even in a push-pull class A design with an EF output stage, only permits about 28W/8R.
The rail voltages then have to be lowered to around 27V also. It becomes obvious that much of the original amplifier design is now redundant and a redesign of the bias controller is necessary.

It has already been said that the class AB amp is best left as is - If you want to try class A, start with a known, inexpensive design rather than be disappointed with a hobbled class AB design that still needs someone else to redesign for you. I suspect it will be cheaper starting with smaller proven design, given the radical changes required to the larger amplifier.

Bear in mind that the largest cost of any amplifier is the transformer, heatsinks and case. If you need to change these, the difference to a new amplifier is not so great.

I have Rcore 1.4 and 2.4kva each for class AB i can still get the unicore which I spoke with a trafo manufacturing company for 7kva! all manufactured as defence grade.

The LME49811 or 810 chip can be biased in class A so thought that can get some cool class A amplification out ouf this...

here is the schematic..
Imageshack - lme49810.jpg

please tell me that can this be biased to get 50w class A?

 

[rhythmsandy]

I agree there are many nelson designs out there but im trying to get class A amplification out of LME49810