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Kora Mercury rube amp

J

Joey Vaz

New Member
I have a Kora a Mercury that has been sitting for about 7 or 8 years in a box. I want to spark it up and test before putting it up for sale. Any precautions I should take prior to applying power to it? I've watched videos where a dim bulb set up is used, but I've only seen this on videos with Solid State receivers. Does the same apply for tube amps?

Thanks!
 
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Sparked up the amp and the controls all work, no noise when turn any of the dials, but the left channel is producing no sound-not even a hum. Attached are some pics of the tubes. They are all lit, but I'm not sure if that means they are working correctly. Any direction on troubleshooting will be greatly appreciated. This unit is very nice looking, in mint condition cosmetically. So I want to resolve the left channel issue and put it in rotation in my setups.

Thanks!


20230219_101949.jpg 20230219_093126.jpg 20230219_102019.jpg
 
Are the tube pind soldered to the PCB? It's hard to tell, but it doesn't look like there are any tube sockets. I was going to say try re-seating the tubes in the sockets, but if there aren't any....
Any fuses on the speaker terminals?
 
EL504 said:
My guess is that they are 'sockets' like in this amplifier (but than of course Noval instead of Loctal 8-pin):

https://www.zumwaltaudio.com/phono

I imagine it being very uncomfortable to have to do a tube change in this amplifier...
Click to expand...
It very well could be. Looking closer what looks like the pins looks to be thicker.
First time I've seen that kind of socket.
I would still try re-seating the tubes. If it worked fine before, one or more may not be making good contact from a sight bump, a bit of oxidation on the tube pins, etc. I had a tubes loose heater voltage due to a loose socket. It happened to one of my son's guitar head amps since it gets moved around a lot.
 
Lavane said:
Are the tube pind soldered to the PCB? It's hard to tell, but it doesn't look like there are any tube sockets. I was going to say try re-seating the tubes in the sockets, but if there aren't any....
Any fuses on the speaker terminals?
Click to expand...
No onboard fuses that I could find.
 
Lavane said:
It very well could be. Looking closer what looks like the pins looks to be thicker.
First time I've seen that kind of socket.
I would still try re-seating the tubes. If it worked fine before, one or more may not be making good contact from a sight bump, a bit of oxidation on the tube pins, etc. I had a tubes loose heater voltage due to a loose socket. It happened to one of my son's guitar head amps since it gets moved around a lot.
Click to expand...

This is my first go at a tube amp. Do I just pull up on the tube? Or do they twist to lock/unlock once seated.

I sent an email to Kora and they responded in less than a day. They stated they have no affiliation with products of this era. The company was sold at some point and they only support the products they put into the market. So I'm SOL in regard to getting a schematic from them. Hifiengine yielded no results either. I will keep searching for info and try to get this amp fully function. The channel that is playing is really clear and sounds great. I know that my ex-boss paid over 3k for this amp when he bought it. He gifted it to me beccuae it needed some work. Cosmetically it is 10/10. Once I get the 2nd channel sorted out, it will go in my collection.

Thanks again for you input!
 
Looks like pin clips soldered onto the board, never seen that elsewhere.
There was a P/P EL34 amp that had the output tubes horizontal & soldered to boards, iirc. Crappy cost cutting.
 
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