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dazling69 16th September 2005 08:53 PM

503 transistor
Hello everyone,
I have been given a DIY project of a pre and power Amp from around 1972 which 'never worked'. I got this without schematics but that is no huge problem as I have almost reversed engineered it. Basically it appears that it uses 108 transistors paired with 503 and the final stage uses 3055 and 2955 transistors.
I am not sure what the transistors marked 503 are (i believe they are PNP) can anyone clarify this?
I also have at least one which is open circuit anyway so does anyone know is there a modern equivalent?



Netlist 16th September 2005 09:13 PM

Because you talk about 3055 and 2955, may I assume that the 503 has some letters too, e.g. 2SC503 or 2SK503.
Also does the amp count 108 transistors or are you again referring to the label?

/Hugo :)

Enzo 17th September 2005 03:52 AM

Actually I might look for 2N503. since the 3055/2955 pair looks like 2N numbers.

2N3055 was a VERY popular NPN power transistor some years back, and the 2955 was its PNP complement.

What package is this 503? TO220?

Eva 17th September 2005 04:26 AM

I think that '108' stands for BC108, I've seen these small signal transistors in old audio equipment quite often.

'503' may stand for 2N503 but I have never seen these.

dazling69 18th September 2005 09:54 PM

thanks for the replies guys,
the 3055 and 2955 have MJE marked on them,, I have found datasheets on MJE3055 and 2955 (NPN and PNP transistors) they are similar to TO220 package type, although they appear slightly bigger and there is a slug where the heatsink tab is (I am not sure when jedec packges where defined). I have made the assumption that the 108 are BC108. anyway the 108 and 503 are similar to the TO92 package type (just a bit squarer looking down)


darkfenriz 18th September 2005 10:03 PM

KD503 used to be popular I think, but I'm not sure if you have them.

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