Information on A940 Transistors

[mickb]

Hi Everyone, i've been asked to look at a cheap power amp that is broken, it has 8 No A940 Transistors which are all blown, the only information i can find for these shows them as PNP's.
I'm not to clever with electronics and would like to know if.
1) A class of amplifier is designed to have only PNP ouput transistors?
2) Does anyone know what A940 transistors could be other than PNP?

Thanks in advance for any information.

[alexcp]

Your A940 must be the 2SA940 - 150V, 1.5A, 25W PNP transistors in TO-220 package. You can probably replace them with MJE15033. It is not common to see only PNP transistors in an amplifier, though.

[es44]

If You put a "2s" in front, it makes it a 2sa940. There are plenty of datasheets floating around when You ask Google.
It happens very very often, that the "prefix" is missing in schematics, honestly a bit confusing.
Best regards
Ebbe

Oops, Alexcp beat me to it

[mickb]

Thanks to both of you for your replies, i've found the information about 2sa940's but what i cant understand is why this amp has only these transistors, the only other transistors in this amp are 3 c1815 and 2 a1015 per channel so if it is not common to see only pnp's in an amp could they be something else?.

[burbeck]

hi Mick
your right it is very unusual, what is the make model of the amp?

[mickb]

It says Liquid power 350 or something like that i haven't got it now.

[mjf]

hello.
2sc1815.................2sa1015;
quasi (complementary) output stages use only one type,here pnp transistors....
they seem to be paralleled.........
i think this kind of amp you have does not deliver much output power.
if the seller acclaims 150w or something else - it is a bad choke.
greetings

[mickb]

Thanks for your reply MJF so your saying that these are PNP's in the output stage?
the a1015's are the LTP but I don't know what the NPN 1815's do.

[Mooly]

As mentioned it will be a Quasi Complementary output... it's not uncommon.

The 2SC1815's will be one of the drivers and perhaps the VAS stage too.

When you power the amp up (if you attempt repair) then use a bulb tester in the mains supply to prevent damage if there should be a further fault causing the outputs to blow.

[Mooly]

Here's an old Quasi design (lifted from an old thread of mine and drawn from memory).

This uses NPN devices as the outputs... but it's exactly the same for PNP... all the devices would be swapped, NPN for PNP etc and the supplies reversed.