Repairing Another Old Guitar Amplifier

in #music2 months ago

Hello, hivers and guitar players!

This guitar amplifier was brought to me for repair a couple of weeks ago. This is a mid 1960s Kent guitar amplifier head. It was probably made some time during 1966, they made this model for about 2 years, 1966-67. This relatively small amplifier puts out about 14-15 watts of power. It uses a pair of EL-84 power tubes and two 12AX7 preamplifier tubes, and has a tube rectifier for the power supply.

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When the amp was brought to me for repair, it had a broken wire to the power switch. The owner of the amp didn't know if the amp would work after the wire was fixed because he had not been able to test it after he got it.

The person who brought it to me also wanted me to put a 3 wire grounded cord in it, for better anti-shock safety. The amplifier had been rebuilt at some time in the recent past, before the current owner bought it. All of the tubes in it are newer, as is the power supply filter.

This is what the chassis looked like after I repaired the broken wire going to the power switch. You can see the old 2 wire power plug pin mount bracket on the lower left side of the chassis in this picture. When the chassis was in the cabinet, that bracket was up against the back of the cabinet, and the 2 wire power cord would be plugged into it through a small hole in the back of the cabinet.

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I removeed the mounting bracket from the back of the chassis and installed a new cord. I chose to install a socket for a removable 3 wire cord. Because the power socket mounts on the back of the cabinet, I had to make a plug for the power wires so that the chassis can be more easily removed from the cabinet if it becomes necessary in the future.

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If you compare the 2 previous pictures, you'll notice that there are several changes to where the parts are on the chassis, as well as a few parts having been replaced with better parts.

After I got the amp wired for power, I tried to test it for proper function. The amp had a loud buzz that was definitely not supposed to be there. I ended up rewiring all the grounds in the amp because of a problem known as "ground loop". This problem is caused by having multiple paths to ground in the circuit, and that causes the amp to amplify AC buzz through the system. After I was done with that, I also installed a longer speaker cord to the chassis. The speaker plug is mounted to the back of the cabinet, and the old speaker cord was short enough to make it difficult to get the chassis out of the cabinet. I also cleaned up some sloppy soldering work that the previous rebuilder had done.
Another thing that I did was to install tube shields for the preamplifier tubes. The shields help to reduce electrical noise interference being picked up by the tube.

This is the tube side of the chassis before I installed the tube shields.

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This is after I installed the shields. You can also see the longer speaker wire in this picture.The black cylinder is the filter capacitor for the power supply

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After all this work was finished, I tested the amplifier again to see how well it worked. I'm happy to say that the repair was successful. This is a good sounding little amplifier. It can get loud, but not overpoweringly loud like more powerful amplifiers can. This would be a good amp for practice, recording purposes, or a smaller venue.

That's all I have for this post, thanks for checking it out!

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I got an old Peavey Heritage guitar amp stowed away in my basement for over 10 years and I'm not sure if its working after all this time. Electronic pre-amp with an old styled Tube power amp. It's been a long time since I played Fender Squire guitar.

If the amp was working when you put it into storage, it will probably still work.
Peavey has made some pretty good amps in the past, both guitar and bass amps.

Great stuff, we send our equipment to an old chap with a crazy studio of electronics to fix our music stuff! Love it !PIZZA

Thanks!

@amberyooper! I sent you a slice of $PIZZA on behalf of @stickupboys.

Did you know you can now buy Rising Star packs with $PIZZA? (9/20)

Good that you did the successful repair of the Amplifier and its working well. Its always great to keep things in a running state however not everyone is so technical to get that happen.

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To support your work, I also upvoted your post!