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mitchelr 10th February 2009 07:47 PM

100w amp ( no O/P transistors )
I have been given a 100w amp board, It was thought that the O/P transistors were ALL 2n3055, ( but I'm not sure) , I was hoping someone will recognize the layout.
Do you think they are all 2n3055 or a couple of NPN's and a couple of PNP's


alexclaire 10th February 2009 08:08 PM


First this is not a class d design !!!!

Look at your module:

The two power transistors that have Emittors connected to -Vee are NPN type by deduction. (collector=case are connected to low value resistor 0,1 to 0,47 ohm maybe)

The two power transistors that are connected to +Vcc (Collector=case) are also NPN.

This is a quasi complementary design.

So All TO3's are NPN type.

2N3055 or better MJ1500X, MJ1502X (don't remember the last figure for NPN type !)

It's very similar to Bernard Corde Module (DAGONE POWER AMPLIFIER) in France. ;)

Hope it Helps.

Could U send me Hi res pictures for information ?

Thanks !

mitchelr 10th February 2009 08:32 PM

Thanks for the quick reply
Sorry I didn't know where to post, ( Not Pass Labs, not solid state, not tube and not a chip amp ).

I will take clearer photo's tomorrow and send

Do you know where I could get some info on the circuit, ie min/max volt supply, current rating of transformer needed.

Thanks for your time

Stuart Easson 10th February 2009 09:06 PM

...this is definitely solid state.

2n3055 has a quite limited Vce, 60v, so that tells you the upper limit of rails, ie +/- 30v. With a stiff enough supply the amp will barely make 50w RMS into a 8ohm resistive load, but with a big enough supply can probably do nearly double into 4 ohms.

50w rms/8r, +/- 28v PK, +/-3.5A peak, 2.5A continuous
100w rms/4r, " , +/-7.0A peak, 5.0A continuous

Good replacements for 2n3055:

mj15003: good robust transistor, but like 2n3055 slooww. Probably only need 1 pair to more than equal 2 pair of 2n3055. Check soar at your supply voltage, or just use 2 pair.

mj21194: better linearity, still a very robust transistor and quicker, probably more expensive. Slight chance of instability.

Have fun


alexclaire 11th February 2009 10:28 AM

You're right,

+/- 30V DC for upper and lower rails are the limit for 2N3055.

If you decide to replace them with MJ15003 for example you could increase rails to +/- 70 V but taking care of the other stages max voltage ratings (Drivers BD239/240, Differential input amp...).
If you don't know how to, don't try to !!!

If you decide to change power transistors only: +/- 30 V is the limit.

so transformer with dual 22VAC secondary 300VA for stereo amp or 160VA for mono amp should do the job.


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