Here is the transistor parts list:
Reference Value Symbol name
--------- ----- -----------
Q 1 ? MG6330
Q 2 ? MG6330
Q 3 MOUNTED ON ONE OF O/P TRANSISTORS MPSA42
Q 4 MJE350 VAS
Q 5 ? MJE15030 driver
Q 6 MPSA92
Q 7 MPSA92
Q 8 ? MJE15031 driver
Q 9 HEATSINK MJE340 VAS
Q 10 MPSA42 VAS
Q 11 MPSA42
Q 12 ? MG9410
Q 13 MPSA42
Q 14 MPSA42
Q 15 ? MG9410
Q 16 MPSA42
Q 17 ? MPSA42
Q 18 ? MPSA92
Reference Value Symbol name
--------- ----- -----------
Q 1 ? MG6330
Q 2 ? MG6330
Q 3 MOUNTED ON ONE OF O/P TRANSISTORS MPSA42
Q 4 MJE350 VAS
Q 5 ? MJE15030 driver
Q 6 MPSA92
Q 7 MPSA92
Q 8 ? MJE15031 driver
Q 9 HEATSINK MJE340 VAS
Q 10 MPSA42 VAS
Q 11 MPSA42
Q 12 ? MG9410
Q 13 MPSA42
Q 14 MPSA42
Q 15 ? MG9410
Q 16 MPSA42
Q 17 ? MPSA42
Q 18 ? MPSA92
It decouples the output stage from the driver stage.
Without it on low volume you would get serious hum.
dear all member,
sorry for diverting subject i want to know these question-
1.what is input bias
2.what is final bias.
3.what is vas bias
4.what final bias
5.what is out put bias
6.what is gain
7.what is feed back
in an amplifier circuit plz explain .thanking you
Look at the circuit in post #32
1. Input bias is the current that flows out of the base of TR1 via R1 and R2.
2. Final bias, output bias. Both refer to the quiescent current that flows in the output stage.
3. Gain. Voltage gain of the circuit is (R9+R7)/R7. So that gives "22". That means 1 volts rms applied to the input will give 22 volts rms output.
4. Feedback means many things. In this circuit it typically means R9 and R7.
Does that help ?
Part of my Maplin collection:
An externally hosted image should be here but it was not working when we last tested it.
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I hate to drag up an old thread but yesterday I bought an old tolex covered wooden box with heatsinks on the back, popped the top off and found 2 maplins amplifier modules inside, along with 2 huge transformers, figured for the sake of a tenner it was worth picking up for just the transformers. I don't have it with me right now but I think it had 4 pairs of output transistors on crudely mounted heatsinks with wires hanging all over the place and I distinctly remember the fuse holders had been bridged with wire soldered in place of the fuse 
From what i've read they were pretty decent modules and I guess it might be fun to try and repair these ones for hifi use. Maybe mount them in a nice metal case. Right now the wooden box they are in is a mess and has 1/4 jack inputs so I assume it was used in a pa system at some point.
Will try and get some pictures up later today.
From what i've read they were pretty decent modules and I guess it might be fun to try and repair these ones for hifi use. Maybe mount them in a nice metal case. Right now the wooden box they are in is a mess and has 1/4 jack inputs so I assume it was used in a pa system at some point.
Will try and get some pictures up later today.
I hate to drag up an old thread but yesterday I bought an old tolex covered wooden box with heatsinks on the back, popped the top off and found 2 maplins amplifier modules inside, along with 2 huge transformers, figured for the sake of a tenner it was worth picking up for just the transformers. I don't have it with me right now but I think it had 4 pairs of output transistors on crudely mounted heatsinks with wires hanging all over the place and I distinctly remember the fuse holders had been bridged with wire soldered in place of the fuse
From what i've read they were pretty decent modules and I guess it might be fun to try and repair these ones for hifi use. Maybe mount them in a nice metal case. Right now the wooden box they are in is a mess and has 1/4 jack inputs so I assume it was used in a pa system at some point.
Will try and get some pictures up later today.
The amplifiers were originally used for a Maplin disco.
I just had one for a mono disco but the record deck cabinet was designed to fit in two.
The amps are 225WRMS into 4 ohms. Mine was very loud,. I used mine in combination with 4 off Fane 50WRMS speakers.
Here is a webpage I did for the Maplin 150 amplifier.
Maplin 150 / 225 watts RMS amplifier from the 1980's.
Maplin 150 / 225 watts RMS amplifier from the 1980's.
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