Need a sub amp badly

[Vivek]

Hi all,
I have two Infinity Reference subwoofers. Each is rated at 300W RMS, 4 ohm and 90dB.
I am thinking of the PA300 or the ETI466 to power them. One of the main problems is that the MJ15003/4 devices are not available easily in India. Moreover, there is a huge problem with fake transistors. Could I replace them with 2N3773/ 2N6609 (140V, 16A)? The latter devices are available more easily.
Secondly, will either of these amps be good for HT subwoofer duties? I will be grateful if any of you could share your thoughts.

Cheers,
Vivek

[Vivek]

Nobody?

[djk]

The 3773 (epitaxial) and 6609 make a fine output pair.

Use three pair for 300W/4R.

[Vivek]

Hi djk,
Thanks for the reply.
The 3773/ 6609 are easily available in India. The stuff is good too and that is why I want to use them. But I understand the sound quality changes in the PA300 with changes in the output transistor. I hope it does not worsen.
Also, I have built several small amps but am not experienced in modifying circuits. How I would be able to accommodate three pairs I don't know.

Vivek

[Nordic]

Originally posted by Vivek
... I understand the sound quality changes in the PA300 with changes in the output transistor....

Probably no more than swapping sets of speakers

[linuxguru]

Apart from ON Semi MJ15003, I believe BEL Bangalore also makes MJ15003 under license (datasheet is available on the BEL website), but I have no idea about how it stacks up against the original in SOA, etc. Also, only the NPN is available, not the complement.

There are a lot of cheap Chinese 2N3773s around, so be careful about the quality. If you find an inexpensive, high-quality, large-die clone, let me know where it's available.

The safest pair now available is the original Toshiba 2sa1943/2sc5200 from Chetan or Darshan, but it's not TO-3, if that's important to you.

[djk]

" I hope it does not worsen."

Bryston used the 2N3773/6609 for many years in their top amplifiers.

Just make sure they are the 4Mhz epitaxial (a few companies still make the slower hometaxial types for power supplies).

[AndrewT]

Originally posted by djk
Just make sure they are the 4Mhz epitaxial (a few companies still make the slower hometaxial types for power supplies).

there's that recommendation again.
How do we tell them apart?

A real 3773 is a great transistor.

[Vivek]

Nordic, I guess that just about settles it. I suppose it is not going to be like the difference between a tube and a SS amp.

Siva, I have the datasheet of the BEL-made MJ15003. But the problem is not having the MJ15004. I could try in other shops but I may still end up getting a fake.

Also, both amps I am thinking of building use TO-3 case output transistors. I have also replied to your e-mail regarding this. But if I get a good 300W/ 4 ohm amp, I don't really care about which transistors it uses. I should probably go to and pick up the transistors. They probably will have the 3773/ 6609 as well because CDIL manufactures them in India.
Which shop is better - Darshan or Chetan?

djk, getting good transistors in India is so difficult because the DIY market is very small. So, we just have to pick up what we find. It's that bad at times. Nevertheless, now that you have mentiond the 4MHz types, I will look out for them.
However, will using the older transistors cause any problems during the operation of the amplfier?

Just like Andrew, I too would like to know.

Cheers,
Vivek

[Vivek]

Hi all,
I just bought 2N3773s from a shop today. The shop I bought it from is a reputed one and the shopkeeper assured me that they are genuine On Semi transistors.
I came home and used nail polish remover and the marking began to rub off after some really hard rubbing. The liquid does not contain acetone but ethyl acetate, isopropyl alcohol, estasol, panthenol, tocopheryl acetate etc etc. Now, with so many chemicals in it, is it natural or am I possibly looking at counterfeit transistors. I could open up one but I don't want to unless there is really no other way I can tell.
Pics attached.