Repairing an Organ: Holiday with Genie does not power up

Holiday with Genie organ

Holiday with Genie organ

I had a recent repair job that I thought was hopeless. I’m not a fan of a million wires, and when I heard about this repair, I knew that if nobody else wanted to repair it, I was going to be challenged.

Well, I accepted the challenge. I went to the owner’s house and began disassembling the organ to gain access to the inside. I found gaining access to be easy, but I was instantly overwhelmed by the number of wire wrapped connections inside. This was a very complex design.

I flipped on the power switch, and I noticed that the baffle around one of the speakers spun a little, so I knew something was working. I tried everything to make some noise, but nothing happened other than making the speaker baffle spin faster. Continue reading

The baby is asleep, and the 6W tube amp is quiet…

It’s 12:11am, August 12, 2010, and I just gave up doing my College Physics to replace the first stage preamp cathode bypass resistor as noted in V1.3 schematic. I sure wish it wasn’t half past midnight :). I have it on 10° or less volume, and 45° EQ, give or take a degree. I’m just guessing. I really want to crank it up to see if the tone and distortion sounds better. 9-6-2010 – It does need some circuit tweaking. It doesn’t sound good to me after all.
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Marshall JCM800 2×12 combo amp repair

Marshall Input JacksI took on a new and simple project today. A friend’s amp started Marshall Circuit Boardgoing on the fritz, and he was ready to give it to the doctor. I’m no doctor by education’s standards, but I love to take what is hurt and broken and make it work again. I derive a pile of joy from the challenge of diagnosis and even more enjoyment when the job is done.

The problem that was described to me was that the amp wasn’t acting normal. The beautiful sound was yucky, and it lacked the power that it once had. Yippeeee! Not in that the amp is busted, but the symptoms describe a simple problem. The output tubes are going out or are on the way out.

I took the amp home and turned it on. I let the heaters warm up, and I watched them as they began to glow. Almost immediately, heat began rising out. I touched my dry finger to the envelope of the output tubes; one was hot, and one was not. Boom. There’s the problem. One of the Electro-Harmonix 6550EH tube’s heaters was burned out.

Output tube Electro-Harmonix 6550EHThe only other problem that I found was that the amp’s low input didn’t work. Upon further inspection, someone soldered the ground wire to the wrong tab on the jack. The hot wire was correct, but the ground wire was not connected to the barrel ring. The jacks are very wobbly so I am going to replace those.

I called up my customer and let him know what was up. He would need two matched  output tubes and two input jacks. Most of the labor will be in the replacement of the jacks. Checking the bias should be fairly simple task, and replacing the tubes will only take a minute.