Unobtainable Power Transistor Fja4313 In The Sc2oo Amplifier Circuit

Hi I have been reading Build the SC200 amplifier part 1 in january edition. The power ouput transistor FJA4313 appears to be unobtainable unles somone knows of a suitable source. I cant find a supplier that stocks this transistor. There is also a mistake on page 22, +/- 56.6V is derived fron 40-0-40 AC secondary transformer not 45-0-45 AC this would give +/-63.6V.  Also led 1 is specified as smd 3216/1206 blue and there are different version of this with 20ma or 30ma forward current also the forward voltage ranges fron 3.2V and 3.6V typical vales. Which one is the correct led and does it matter.


Regards

The FJA4313 is equivalent to the 2SC5242 according to this datasheet.  I'm in Australia so I get the Aussie sites but you can try Mouser UK here.  Farnell / Element 14 list it but don't have it in stock.  It appears they are around so best do a bit of googling.  
Re the transformer specs.  I have not seen the circuit but yes, although a 40-0-40 transformer will give you 56.6V on full wave rectification, that will drop as soon as you put any load on it.  A 45-0-45 would make sure that you'd still have 56V rectified even when putting a load on it.  But the designer would be best placed to comment on this - Alan Winstanley, can you comment further?

Hi the FJA4313 FJA4213 do appear to have direct equivalents acording to data sheets. Refering to the voltage issue, transformers have a regulation value ie a 40-0-40 300va is 6% higher on no load. the voltage drops gradually down to its nominal value when full load is reached, it does not suddenly drop when you apply a small load, i have tested this with a 250 va torroidal increasing the load and observing the voltage drop. Also uk transformers are rated at 230v ac input, the uk supply is 240v nominally so the a 40-0-40 torroidal will have a ratio of 230 / (80*1.06) = 2.7122, with the uk supply the actualy ouput will be 240/2.7122 =88v ac or 44-0-44 on no load. this more than takes care of any voltage drops in the amplifier power supply.

I wouldn't like to second-guess the designer but I'll  ask the question and come back with any information. Might take a day or two as everyone is on holiday.

I look forward to reading the response from the designer.

Apologies for the longer than usual delay over the holiday period,  please find answers below.1) FJA4313OTA is available from Digi-Key at the link below, or as part of a
set of hard-to-get parts from our SILICON CHIP Online Shop:
https://www.digikey.com/product-detail/en/on-semiconductor/FJA4313OTU/FJA4313OTU-ND/1056495
http://www.siliconchip.com.au/Shop/20/4140
2) Regarding the transformer, you are indeed correct. The transformer should be 40-0-40 not 45-0-45.
3) LED1 is supplied with around 2mA so any blue LED of that size should be
fine. The forward voltage is not important as the circuit will automatically
adjust to compensate (it's supplied from a constant current source).I hope that helps.

Hi Alan does it matter which version of BC546 is used, ie BC546B, BC546C and also can BC556B be used for the SC200 power amplifier.
The B and C version appear to have a higher gain.
RegardsHeath

Hi Alan regard the SC200 amplifier design  i have a query about the 4.4mV drop each emitor resistor Re. I read elsewhere specifically in Randy slone power amplifier construction manual and douglas self power amplifier handbook that the optimal V drop for low distortion with emitter follower output stages need to have a much higher voltage drop across each emiter resistor ie Randy slone quotes a value of 47mV and Douglas self quotes 50mV. With Re restors of 0.1 ohms this means the current per transistor pair should be 0.047 / (0.1 x 2) = 0.235 Amps.  So total current for both sets of ouput transistors = 2 x 0.235 = 0.47 Amps. These values do seem ridiculously high to me but the fact that 2 different Authors have quoted very similar Re Voltage drops for emiter follower outputs circuits raises the question why this design has only 4.4mV.Am i getting confused misunderstood about emiter follower output stages and the optimal biasing required ????.

RegardsHeath