Power amplifier with multiple 2SA1943/2SC5200 transistor pairs

Hi,

I'm referring to this URL. Could anyone please explain to me what the author means with the following statement:

The Far East quite a popular hi fi BJT transistor amplifier module for full power output transistors 4 2SC 5200 and 2S 1943 should be tested one at each used test voltage +-35v accordingly, the power will be lower for full power supply voltage pretty high, build and test stages be careful of capacitors and transistors link circuit voltage without checking whether it is correct to give.

As far as I can see it, he advices not to mount all four pairs at once, but to solder in one pair after the other and check the amp in between at a lower supply voltage. But what does he mean with the rest?

TIA and best regards!
 

Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
I think it means that caution in adding the extra pairs of output devices is advised. So it should be with arbitrary, open wired connections. Note also that the supply rails of +/- 95V are unsuitable for devices like 2SC5200/A1943. Look at the transistors' SOA graphs. I suggest these are not appropriate parts, just the cheapest ones. If such high voltage rails are needed to get 400W, better to use MJL4281/4302 or similar devices with better (higher voltage) SOA.

Also, it suggests instability is likely with arbitrarily wired multiple pairs, so base stopper resistors and care with layout will probably be required. That's sensible but not easy for beginners without instruments like an oscilloscope. Unless you are experienced with high power construction, I wouldn't use this amplifier at higher than 60V rails or 2 pairs of output devices.

Personally, I wouldn't touch it - spend a little more on a PCB that incorporates all the necessary components.
 

nec3

Member
2005-06-21 5:08 pm
Ankara
Hi,

I'm referring to this URL. Could anyone please explain to me what the author means with the following statement:

The Far East quite a popular hi fi BJT transistor amplifier module for full power output transistors 4 2SC 5200 and 2S 1943 should be tested one at each used test voltage +-35v accordingly, the power will be lower for full power supply voltage pretty high, build and test stages be careful of capacitors and transistors link circuit voltage without checking whether it is correct to give.

As far as I can see it, he advices not to mount all four pairs at once, but to solder in one pair after the other and check the amp in between at a lower supply voltage. But what does he mean with the rest?

TIA and best regards!

You are right.

He most probably used Google Translator.

He says, "the test was made with only a pair of output transistor and +-35V supply voltage and so output power was low.. For full power, required supply voltage is pretty high and 4 pair is needed."
 
Thanks a lot for your replies!

Ian, your thoughts are mine as well. I'd not use the suggested PCB, especially 'cause wiring the output devices is a no-go for me. We did that with transistors in TO-3 packages in times when we had no other choice, but these TO-264 devices require to be soldered onto - meticulously designed - PCBs.

I think the amplifier's circuitry, basically an internally compensated power OpAmp, isn't that bad at all, despite of it's lack of output protection. Just add two transistors plus a hand full of passive components for a short circuit protection and a reliable protection against arbitrary DC at the output, and then design a good PCB, and it will do a good job.

And you're right also in terms of devices' costs. At least here in Germany I have to pay for one MJL4281 or 4302 (from ONS) or MG6330-R or 9410-R (from Semelab) the same as I did for two pairs of 2SA1943/SC5200 :). Nonetheless, as you said, I'll have to go for them.

Best regards!
 
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