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Old 27th September 2010, 07:23 AM   #1
mickb is offline mickb  England
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Default Information on A940 Transistors

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.
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Old 27th September 2010, 09:02 AM   #2
alexcp is offline alexcp  United States
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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.
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Old 27th September 2010, 09:05 AM   #3
es44 is offline es44  Denmark
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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
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Old 27th September 2010, 09:31 PM   #4
mickb is offline mickb  England
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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?.
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Old 27th September 2010, 11:50 PM   #5
burbeck is offline burbeck  United Kingdom
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hi Mick
your right it is very unusual, what is the make model of the amp?
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Old 28th September 2010, 06:56 AM   #6
mickb is offline mickb  England
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It says Liquid power 350 or something like that i haven't got it now.
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Old 28th September 2010, 08:52 AM   #7
mjf is online now mjf  Austria
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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
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Old 29th September 2010, 07:13 AM   #8
mickb is offline mickb  England
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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.
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Old 29th September 2010, 07:25 AM   #9
Mooly is offline Mooly  United Kingdom
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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.
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Old 29th September 2010, 07:33 AM   #10
Mooly is offline Mooly  United Kingdom
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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.
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