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It was a dark and stormy night.....I got a broken Fender Bassman 70 amplifier into my shop. The first thing I did was a quick visual inspection. Then I plugged it into my dim bulb tester and turned the amp on. The red amp indicator light did not light and the dim bulb did not light. I turned the amp off and pulled the fuse. The fuse was blown and I replaced it with same value (2.5 ). I turned the amp on and the dim bulb went to full brightness. I turned the amp off, removed the back cover and pulled all the tubes.
I turned the amp on and the bulb went to full brightness. I turned the amp off and the dim buld turned off but then the dim bulb turned on.....but the amp switch was off! Then it flickered and I smelled a burning smell. So I pulled the plug from the tester.
As I was removing the chassis from the cabinet I was thinking to myself that the power or output transformed must have just burned up ($$$). I looked around and did not see anything that was obviously burned but boy could I smell it! After it aired out I sniffed around the transformers but did not smell it that strong. I could not find the offending component.
As it turns out the lead to the power switch was burned and the switch was burned. I removed the switch and tested it. Sure enought there was a resistance from one of the leads to the threaded shaft (which is grounded to the chasis).
I have never run across this issue. I have had switches that did not work or where the bats were loose or the case was broken but never shorted especially to ground!
I turned the amp on and the bulb went to full brightness. I turned the amp off and the dim buld turned off but then the dim bulb turned on.....but the amp switch was off! Then it flickered and I smelled a burning smell. So I pulled the plug from the tester.
As I was removing the chassis from the cabinet I was thinking to myself that the power or output transformed must have just burned up ($$$). I looked around and did not see anything that was obviously burned but boy could I smell it! After it aired out I sniffed around the transformers but did not smell it that strong. I could not find the offending component.
As it turns out the lead to the power switch was burned and the switch was burned. I removed the switch and tested it. Sure enought there was a resistance from one of the leads to the threaded shaft (which is grounded to the chasis).
I have never run across this issue. I have had switches that did not work or where the bats were loose or the case was broken but never shorted especially to ground!
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