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Old 19th April 2014, 09:30 PM   #101
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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
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Old 5th June 2014, 12:52 AM   #102
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Quote:
Originally Posted by GEirin View Post
Hi all.
Someone could explain the function of C9. Improves sound?
Thanks
It decouples the output stage from the driver stage.
Without it on low volume you would get serious hum.
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Old 9th July 2014, 01:14 PM   #103
masood is offline masood  India
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Quote:
Originally Posted by nigelwright7557 View Post
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
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Old 9th July 2014, 01:45 PM   #104
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by masood View Post
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 ?
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Old 10th July 2014, 12:25 PM   #105
masood is offline masood  India
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Quote:
Originally Posted by Mooly View Post
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 ?
dear mooly
thanks for explaining.thanks a lot
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Old 2nd December 2014, 10:15 PM   #106
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Quote:
Originally Posted by Mooly View Post
The MOSFET one is well documented as you probably know, with a lot of copies and variations as well.
The 50 watter, not seen a circuit for that for many years.
The big one. That was a really basic circuit I seem to remember, a classic textbook simple amp. Something like an input pair, VAS and drivers, nothing else, no CCS or anything. You just hung outputs on the end of it.
50 watt info here:
50W HiFi Power Amplifier LW35Q Maplin Kit
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Old 2nd December 2014, 10:26 PM   #107
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Part of my Maplin collection:
Click the image to open in full size.
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Last edited by nigelwright7557; 2nd December 2014 at 10:38 PM.
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Old 6th March 2015, 10:50 AM   #108
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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.
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