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AU-919 Worst Case Scenario

ivandezande

ivandezande

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ivandezande said:
View attachment 2361073
NTE drivers and outputs on one channel.

I’ve seen these:
https://www.audiokarma.org/forums/index.php?threads/new-to-3-output-transistors.260131/

https://audiokarma.org/forums/index.php?threads/au-919-output-transistors.295985/

But just want to be sure, I’m stuck with MJE15032/3 and MJ21193/4? Kinda bummed, my friend paid good money for it, but that’s how it goes. It does work.
I know about the TTA's for the drivers, but want to stick to TO220 form factor.
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No you are not. 2sc4883a/2sa1859a are still available thorough arrow. (120Mhz(NPN)/60MHZ PNP). Those are TO-220F so you still will need to be creative but those have much better SOA than TTA If you do not want to get all bunch of those then i just stock up and can land you a couple ;)
 
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Now regarding Outputs. Remember that Ft is a function of collector current. I would seriously consider NJW3281G/NJW1302G. for this task if you compare the curves Ft(Ic) from datasheet i would say they are very comparable (sanken you mentioned may be slightly faster at higher collector currents) but Power wise NJW are the beasts and you would have very robust output stage.
 
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ivandezande said:
I know about the TTA's for the drivers, but want to stick to TO220 form factor.
Click to expand...

For the drivers, I used 2SA1011 and 2SC2344, I could get them NOS in Thailand but you can get them in the US. did you consider these?
For the outputs, @GrisPato gave you a good suggestion. But you can also use TO3P transistors like 2SA2223A and 2SC6145A, or the ones you suggested.

EDIT:
I forgot to mention I committed a sacrilege: I have an AU-D907 where I used the MJ21195 and MJ21196.
 
JoseHH said:
For the drivers, I used 2SA1011 and 2SC2344, I could get them NOS in Thailand but you can get them in the US. did you consider these?
For the outputs, @GrisPato gave you a good suggestion. But you can also use TO3P transistors like 2SA2223A and 2SC6145A, or the ones you suggested.

EDIT:
I forgot to mention I committed a sacrilege: I have an AU-D907 where I used the MJ21195 and MJ21196.
Click to expand...
@JoseHH By the way i spoke to owner of AmpsLab (link you sugested on the other threads) and according to him 2SA1011/2SC2344 he bought long ago before china fakes. One just has to decide if he wants to trust his words. So possibly it is an option as well. But again 2SC4843a/2SA1859a should be fine and for outputs I would use 2SA2223A / 2SC6145A which are scheduled for EOL or On Semi NJW3281G/NJW1302G. And i would lean towards the On Semi as i do see that Ft(Ic) graphs for On Semi are the same but they seem more rugged. By the way i used NJW in AU-D7 which is relatively fast amp ( and the one that is very accurate in my opinion) and they sounded very well.

EDIT. I just glanced @ datatasheet for Sanken and Onsemi Sanken lists 35MHz @2A Vc = 10V (2SA2223A). and OnSemi lists 30 MHz for 1A Vc = 10V. If you look @ the graph then you will see that for Onsemi @2A Ft is around 50Mhz. (Actually graph for both is Ft(Ie) not Ft(Ic) which is basically same thing here). .One really need to be careful in manupulating those numbers. Look @ the graph for 2SA2223A Ft drops below 10Mhz for currents less than 50ma


I also just checked B&D has several 2SA1011/2SC2344 in stock I would not miss that chance
 
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Hello Deniss, you are correct, the NJW3281G/NJW1302G you are recommending are a good choice since Sanken will no longer produce the ones i suggested.
With regards to Amplab's 2SA1011/2SC2344, the pictures of the parts look identical to the Sanyo parts I got in Bangkok, and also they look identical to those that B+D sells so I concludes that they must be authentic, but I never bought from Amplabs. The transistors I used were tested up to 130V or so, and they passed the DC current that the datasheet specifies at that voltage without suffering any degradation in hfe. But more importantly, they are working in my AUD-907 for 3 years, so the chances of them being fakes is low. I see many fakes in the yahoo auctions in Japan, where it is still possible to get 2SD381/2SB536 but there are fakes of these as well. I noticed that the OP is located in the US, and this is why I recommended this source which by the way is one of the few that has the KSC1845/KSA992 in stock at the moment, among other useful parts.
 
Hi Jose, I got myself 10 pairs of 2SA1011/2SC2344. I completely agree with you that those probably would be the best choice as looking @ the graph of Ft(Ic) making this transistor sort of unique as i see that even at very low colector currents Ft is high.
 
Ivan,
if you go TO-3P route with output transistors and this amplifier well deserves it, I would recoment spend extra 20 USD and get this Thermal pad :
https://diyaudiostore.com/products/keratherm-transistor-insulators
it is Keratherm 86/82 - pads cut specifically for TO-3P and thermal conductance is high. Some folks at diyAudio experimented and concluded that it was better than mica + grease in heat transfer.
As a plus no more mess with thermal paste as it explicitly states that NO grease. Minus it is more expensive.

Deniss
 
TupolevFan said:
No you are not. 2sc4883a/2sa1859a are still available thorough arrow. (120Mhz(NPN)/60MHZ PNP). Those are TO-220F so you still will need to be creative but those have much better SOA than TTA If you do not want to get all bunch of those then i just stock up and can land you a couple ;)
Click to expand...
Looks like B-Dent has them.

NJW's are out for a long time everywhere, so looks like I'm going 2SA2223A/2SC6145A for the time being.
Still confused by all the options!
 
IF the outputs test good why do you need to change them? Is it because you should do both sides with the same type of output devices or is it because you all hate NTE products? I'm confused.
 
Either of the TO3p options is fine. The ON parts are in stock here:

https://www.arrow.com/en/products/search?cat=&q=njw3281&r=true
https://www.arrow.com/en/products/njw1302g/on-semiconductor,
and Arrow still has the driver transistors 2SC4883A/2SA1859A (keep in mind that these have insulated tabs so it a bit more involved to use them in the AU-919 which uses the metal tab as a connection).

Digikey still has the Sanken pair 2C6145A/2SA2223A, if you want to use them as outputs. Please don't forget to ask them to sell you all Y rank or all O rank. Otherwise they may send you some Y and some O.
You may choose the 2SA1011/2SC2344 from Amplabs and the power transistors from either Arrow or Digikey, or you could go all with Arrow.

Important notes about mounting new outputs:
If you use the TO-3p parts in the AU-919, you will see that in order for them to fit in place you will have to saw a corner of the transistor tab. No big deal with this, as long as you cut with a saw and file the cut after. Please avoid clipping it with wire cutters as this will bend the metal tab of the transistor in detriment of a good thermal contact with the heat sink.
There is an issue with the leads and the socket type of the AU-919. Echowars posted about this here, and mentioned about why one should care about insulating the E and B pins from the heatsink. Member Ilimzn in a Croatian audio forum was the first to addapt the TO-3p parts in the AU-919.
The B and E leads of the transistors could be bent into the holes, but you will have to insulate them very carefully (preferentially with a teflon sleeve). Alternatively, you can adapt pins and cut the legs like Hyperion did when he used these transistors in a BA-F1. Note that the design of the heatsink in the BA-F1 is different and John did not need to cut the corner of the transistor tab.
There are other pins that you could use (these, for example will fit snugly in the socket, but require an insulation), and drilling a hole in the wide part of the transistor lead, and passing through a pin, or a suitable copper wire, and using an insulation sleeve.
 
JohnT123 said:
IF the outputs test good why do you need to change them? Is it because you should do both sides with the same type of output devices or is it because you all hate NTE products? I'm confused.
Click to expand...
Nothing personal about NTE. The rationale is that these NTE parts are very different from the parts of the other channel with ft= 4MHz. The NMA1012/NMC1012 have a transition frequency close to 30MHz, and this is one of the distinctive features of these amplifiers. Sanken initially made the NMA/NMC specially for Sansui with a non magnetic case, but continued production of similar parts, first in standard TO-3 case (2SC2606/7, 2SA1116/7, discontinued them and keep producing equivalent parts TO-3p until recently.
Remember that the transistor with ft=4MHz starts to roll off at a frequency fc=ft/hfe which would be lower than 100KHz for the NTE parts. This speed, or slew rate limitation imparts distortion components in the audible range for reasons that have been discussed in other threads in this forum. Besides this, some claim that they hear the difference between an amplifier with the original fast transistors and one with the 4MHz devices.
 
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