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Old 14th March 2008, 02:06 PM   #1
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Join Date: Feb 2008
Default repair'-Acoustic 450 distorted and low volume. Transistor crossover distortion?

Acoustic 450 guitar/bass solid state head from the 70's.
It has low volume and it is distorted when it is cranked up.

Rail voltages are there and no transistors are blown. Although the rail voltages on 3 output transistors are 45v, and the other 3OPT are 90v. I think its just the design of the amp, which does seem odd...

It has a mix of output transistors: two are MJ15001
4 are 480037/(i think)2N3055
The two MJ15001's i think were from a repair in the past.

Blown or damaged coupling capacitors? got the idea from a reading. Anyone have the schematic?, i may just have to buy it.
I may have missed something or forgot about something i found. I will update this later today after a get some sleep. I will have to double check the rail voltages.

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Old 14th March 2008, 02:39 PM   #2
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Join Date: Feb 2008
Maybe the repairman who changed the OP transistors forgot to readjust bias.
MJ15001's and 2N3055's charasteristic are really different! This could cause that distortion. I would employing same OP transistors.

You wrote that it's from 70's. Then a complete "re-capping" is needed (let's renew all the elkos!). You are right, a dry elko could cause disortion too.
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