Hi, I have a Marshall G100R cd which I found in my friends garage, he said it had a problem and it kept blowing the fuse.
I checked it out and found tr9 and tr10 the darlington drivers were short, I replaced them and after further checking discovered 3 x 33 ohm resisters in the power stage which were also short circuit I replaced them and powered up the amp. All was well so I connected a cab and used a guitar on the i/p, the amp seemed to work fine but had very little power, it was only giving out about 10 watts, everything on the preamp worked as it should.
Is there someone who knows about these amps who could guide me, I dont have a scope or signal generator and have exausted my multimeter. All the rails seem fine, apart from 2 x 7watt resistors getting a little hot, I cannot see anything that could cause this lack of gain. Please help if you have any ideas, thanks, Peter
I checked it out and found tr9 and tr10 the darlington drivers were short, I replaced them and after further checking discovered 3 x 33 ohm resisters in the power stage which were also short circuit I replaced them and powered up the amp. All was well so I connected a cab and used a guitar on the i/p, the amp seemed to work fine but had very little power, it was only giving out about 10 watts, everything on the preamp worked as it should.
Is there someone who knows about these amps who could guide me, I dont have a scope or signal generator and have exausted my multimeter. All the rails seem fine, apart from 2 x 7watt resistors getting a little hot, I cannot see anything that could cause this lack of gain. Please help if you have any ideas, thanks, Peter
Hi, the resistors are 7 watt and marked R33j. I have just checked the diagram and they are 0.33 ohms. I have still got the origional they seem to be measuring 60 ohms, but I think my multimeter cannot measure them. I will have them checked, I must thank you for recognising my error, may I ask the two resistors in the psu 270 ohm 7watt and on the -ive 330 ohm 7w are they supposed to get hot. Thanks, Peter
Pitagi
i would like to know what your using in terms of a multimeter make model
secondly when you measured these resistors where they still in circuit or had you removed them
i have a mental image of you holding a resistor (out of circuit) and with your thumb and forefinger pinching the lead of the resistor to your test probe and your other hand doing the same thing and looking at the reading on your meter with a puzzled look
what is the average resistance of the human body paralleled by a fractional ohm's resistor?
i would like to know what your using in terms of a multimeter make model
secondly when you measured these resistors where they still in circuit or had you removed them
i have a mental image of you holding a resistor (out of circuit) and with your thumb and forefinger pinching the lead of the resistor to your test probe and your other hand doing the same thing and looking at the reading on your meter with a puzzled look
what is the average resistance of the human body paralleled by a fractional ohm's resistor?
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Hi, sorry for the late reply, yes I am using a cheapo multimeter but having spent much of my early days working for Acoustic Research , Recording Studio Designs teac etc I do know how to use a mutlimeter. I think the problem is my eyes, they are not as good as they should be and to look at a 10 year old resistor for a decimal point is a easy mistake ( should have checked the diagram first). The problem is now solved and I have the gain that was missing. I have decided to invest in a fluke multimeter and at some time to get a signal generator and scope. Thanks for the interest you have shown in my post please keep in touch.
Ps I had a good sesion with the amp today, I think it is just as good as the valve state. Regards, Peter
Ps I had a good sesion with the amp today, I think it is just as good as the valve state. Regards, Peter
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