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Old 4th August 2007, 02:22 AM   #1
diyAudio Member
Join Date: Jul 2004
Location: PA
Default Silvertone 1482 Blowing Rectifier Tubes

I picked up this amp as a 1st project to "restore". Did the dim bulb tests with and without the 6X4 rectifier in and looked good.

Hooked up a 6ohm? computer speaker to it without the dim bulb and everything seemed fine. I actually played on it for about 5 min. Hooked up my 8ohm 1X12 cabinet and blew the power tube as well as the fuse. I originally replaced the ps caps with 47uF, 10uF, and 10uF where the schematic calls for 20uF, 10uF, and 5uF. The data sheet on the 6X4 states 10uF should be used.
After reading a post hear about the 6X4 and caps, I tested the resistance of the original PS cap and found that the leads go to infinity. So I rewired the original PS cap back into the circuit and tested again. Same problem. Here are my observations:

-The rectifier tube passed the dim bulb test with both speakers hooked up. Bulbs do not glow brightly.

-With all of the tubes in, it works fine with a 100W bulb in the tester. However the bulb is glowing brighter than before. I can actually hook up a guitar and play into the 8ohm cab.

-With all of the tubes in and plugged directly in the wall, I watch the voltage going up on from the recitfier to about 260V then the heaters in the rectifer start glowing brighter and brighter and the voltage starts dropping to about 250V then the fuse and rectifier tube both blow. The schematic says the voltage should be 350V.

I was wondering if I hooked up the speaker to the wrong tap. There are no markings as to which tap is which. Just 3 wires coming from the output transformer (one being ground). I know the amp came with either 4ohm or 8ohm speakers. Is there any way I can tell with a meter which tap is which?

Heres the schematic:

Thanks to all that can help this boob...I mean noob.

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Old 4th August 2007, 04:06 PM   #2
diyAudio Member
Join Date: Jul 2004
Location: PA
Well, I found the answer. After reading another post about checking for shorts by testing the resistance to ground on the B+ side. I tested the resistance from each of the points where there was a voltage measurment on the schemtaic. I found the capcitor that is parallel to the resistor that ties the cathode to ground was shorted. I removed it and everything works great.

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