Hi everyone,
I'm new to the forum and looking for a little guidance. I'm a ham radio guy and do some restoration work on tube radios. I'm far from an expert and even farther with solid state devices.
I went to the dump the other day and when I was emptying my truck noticed a big ass amplifier sitting on the side. I couldn't resist so once I had the truck emptied I loaded up the amp. When I got it home I discovered it was a Kasino 200U which is a 200watt amplifier with two 15" speakers. My original thought was to salvage parts from it but after looking it over it seemed to be intact.I should mention that I have zero musical ability and no guitar or bass. After a visual examination of the amplifier and finding only minor evidence of previous work I decided it may be worth fixing.
I started checking with the power supply and found it working but the primary rails which are suppose to be +- 39.5v were both about 2v low and the 8v rails which are +-8v were about .4. high. These values didn't seem way out of line so I went on to power up the amp. Long story short the amp didn't work. I went on to troubleshoot and determined that the pre-amp board and all of the controls seem to work correctly. I determined this by putting a signal tracer on the pre-amp output and I could hear a signal and it responded to adjustment of the controls. I was using audio from my computer into the input of the amp for a signal. When I hooked up a speaker to the output I got no output at lower volume but as I increase volume I started to get bursts of audio much like a dirty pot would give and at higher volume toe burst get more frequent. I'm attaching a copy of the schematic for the amp board.
Here are the things I have done so far to try and determine the problem.
Thanks in advance for any help you can provide and I will try to be responsive to any suggesting you might have.
Jon
I'm new to the forum and looking for a little guidance. I'm a ham radio guy and do some restoration work on tube radios. I'm far from an expert and even farther with solid state devices.
I went to the dump the other day and when I was emptying my truck noticed a big ass amplifier sitting on the side. I couldn't resist so once I had the truck emptied I loaded up the amp. When I got it home I discovered it was a Kasino 200U which is a 200watt amplifier with two 15" speakers. My original thought was to salvage parts from it but after looking it over it seemed to be intact.I should mention that I have zero musical ability and no guitar or bass. After a visual examination of the amplifier and finding only minor evidence of previous work I decided it may be worth fixing.
I started checking with the power supply and found it working but the primary rails which are suppose to be +- 39.5v were both about 2v low and the 8v rails which are +-8v were about .4. high. These values didn't seem way out of line so I went on to power up the amp. Long story short the amp didn't work. I went on to troubleshoot and determined that the pre-amp board and all of the controls seem to work correctly. I determined this by putting a signal tracer on the pre-amp output and I could hear a signal and it responded to adjustment of the controls. I was using audio from my computer into the input of the amp for a signal. When I hooked up a speaker to the output I got no output at lower volume but as I increase volume I started to get bursts of audio much like a dirty pot would give and at higher volume toe burst get more frequent. I'm attaching a copy of the schematic for the amp board.
Here are the things I have done so far to try and determine the problem.
- Removed and tested the final transistors(RCA 36892) using a DMM on the diode setting. They all test good.
- Removed and tested Q9(RCA 38737) which is the driver for Q22. Again tested with a DMM and good.
- I tested all of the diodes on the board and they test good with my DMM.
- Tested all four 1 ohm 5w resistors on the drivers and found them good.
- I tested all of the resistor on the board in circuit and found none open or shorted. Values all seemed reasonable.
Thanks in advance for any help you can provide and I will try to be responsive to any suggesting you might have.
Jon
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