Mj15003 And Mj15024
Straight out I have to admit a severely limited knowledge. I'm a user, not a builder. I aquired an old Studiomaster 400C power amp. I can't get details on it anymore.
While I was trying to establish if it is 200W into 4ohms or 8, I noted that one channel uses 4 x MJ15024, The other 4 x MJ15003. What is the difference?
I understand mached pairs but why all the same on each channel. Why not use all the same type?
Lastly both of these device are rated at 250w@ 55V, so why would I need 4 per side?
Confused of london
It sounds like one channel has been rebuilt at one stage.
Go to On-semi to get specs of these two transistor types.
The output stage is quasi complimentary design - not uncommon in older amplifiers.
Multiple output transistors ensure SOAR limits are not exceeded.
The MJ15024 is higher voltage rating transistor (250V vs 200V). For the amp power you are describing, the 15003's would probably be ok. The 4 transistors per channel could be two parallelled pairs, or could be 2 series pairs using 4 power supply rails, which keeps heat dissipation low (a few high end amps use this arrangement).
You can get a bit of an idea about power rating by measuring the DC power supply rails: +- 55volts or so would give 200W into 4ohms, whilst around +-67volts would be needed to produce 200W into 8ohms.
So I could heat up the amp just by increasing the voltage? One of my hastles is the 4 ohm load whereas most comertial cabs are 8ohm.
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