1961 112 Revival Blowing Main Fuse

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Lucent
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Joined: 2007-06-17
1961 112 Revival Blowing Main Fuse

TIME FOR A NEW FORUM TOPIC..... JUST TO WAKE UP THE LAST FEW EARTH OWNERS OUT THERE. :-)

My 1961 112 Revival was making a lot of hum noise so I tried a different set of tubes in it and it was nice and quiet. Took the loaner tubes out and ordered a new set of Electro-Harmonix 6L6GC from the Tube Store. (Great Service & prices by the way. www.thetubestore.com)

While I was waiting for my new tubes I sprayed cleaner on all the contacts, pots, jacks, etc. and gave them a good workout.

Get my new tubes, install them, and throw the main power switch. Click. And the main fuse blows. WTF Try another fuse, same thing. Switch back to the original tubes, that worked, but were noisy. Same thing... Blown fuse.

The fuse that was in it, and my other non working Revival were 2.5 amp (250volt?). Looks like the schematic calls for a 5 amp. Do I dare put a 5 amp fuse in it and turn it on?

Thinking back I probably sprayed the main power switch and stupidly clicked it back and forth when it was plugged in and the tubes were out. But it didn't blow the fuse then.

Anybody have any ideas? What could I have done by cleaning it? It was off but I think it was plugged in.

L

Lucent
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Joined: 2007-06-17
So I took it in for repair.

So I took it in for repair. Had a shorted rectifier in the power supply. Blew out just sitting there with no tubes in the amp while I was cleaning the pots I guess. :-)

Seems that somebody had replaced one of the four in the curcuit with the wrong kind. All four now replaced and amp back running. Also had a hum due to needing new filter caps. With all of that it should good as new. I think he can also get my 2nd Earth back to new as well.

On an interesting side note. We have had several discussions on this board about what Ohms these amps run at. This one checks out at 4 Ohms. His voice mail says it is 36 watts into 4 Ohms, 32 Watts into 8 Ohms, and 21 watts into 16 Ohms. And this particular amp has a 16 Ohm speaker installed. My other Earth has an 8 Ohm speaker that I know is the original.

I was under the impression it was a 60 Watt amp. Maybe I am misunderstanding his voicemail and it is really 64 watts at 4 Ohms. That would make more sense. Use it with an external cab to get it to 4 Ohms. That would work correctly with the original speaker. 8 Oms as a combo with 32 Watts, and then full power with the cab at 4 Ohms.

L

Lucent
Offline
Joined: 2007-06-17
Both amps have now been fully

Both amps have now been fully restored and are operating like new. Here are the repair notes if anybody is interested. The Amp repair shop owner is very good at fixing vintage amps. After some discussion we decided to do the full restoration on both of the amps.

AMP 1: We began this project by disassembling the amp and tracing the short circuit down to defective and unmatched diodes in the high voltage power supply; replaced same. After consulting with the customer, it was decided to rebuild the power supplies replacing all the original electrolytic capacitors. It was also decided that we would replace the on/off/on power switch with a standard Fender type off/on. This was done as we installed the new switch and reconfigured the AC primary wiring to proper polarity and grounding. We then moved on to both the high voltage and bias power supplies where we replaced all the filter capacitors.

Reassembled amp re-installing output tubes supplied by the customer and re-calibrating bias for same. All amp functions check OK with amp driving 40+ watts RMS into a 4 ohm load. NOTE: This amp has an 8 ohm speaker.

AMP 2: Disassembled amp and began restoration by replacing the AC line cord (old cord taped up) and correcting polarity and ground wiring. Rebuilt both power supplies per agreement with customer replacing all power supply electrolytic capacitors. Installed new output tubes and re-calibrated the output bias.

Found huge difference in gain between both amps; this amp had far less. Traced the problem to defective wiring of the input jacks. Physically traced out the input wiring of the other matching amp (which was working properly) and rewired this amp exactly the same.

After initial re-assembly, found that the reverb was working intermittently. Disassembled and traced reverb problem to an intermittent pin connection on the PC board; corrected same. Reassembled amp once again and all functions then checked OK with the amp driving 40 plus watts into a 4 ohm load. Note: This amp has a 16 ohm speaker. (I am replacing the old 16 ohm speaker with a new 8 ohm speaker - L)

I am a very happy camper even though the repair cost was probably as much as the amps are worth. But hey, now they are almost like new. And they sound excellent!

L

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