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Kora Triode 100 SB Mono Block Power Amps

I have recently agreed a deal to buy a pair of the above from a pre-owned hi-fi dealer and who has sent the amps off for testing prior to sale and his engineer will be renewing the MOSFET capacitors and repairing a valve connection.  

Back in 1997 these amps were measured, reviewed and recommended by Bascom H. King, so I thought that was a good reference point to begin my first venture into valve amps. 

I would be very grateful to know if any members here have owned or heard these amps in the past and in a particular if they have any experience of biasing with this model?

Here’s some more info from the net:

“These mono blocks use the Russian 6C33CB output tube, 6922 for input, and the 6BQ5WA for driver stage to achieve 80 watts output power. An incredibly high 115db signal to noise ratio, superwide 10Hz to 60kHz bandwidth, and a low rated distortion of only .07% @ 1 watt might just make those 'tube measure bad' naysayers finally concede in defeat. This triode amplifier uses metal film resistors, polypropylene capacitors, silver solder, gold connectors, double-sided circuit board and more make this unit so good and reliable that Kora guarantees this unit for two years"

Thanks very much.    

soma70
trelja
3,215 posts
 
Al makes a good point on the tube sockets, as these 6C33B tubes tend to more quickly eat through them than most any other.

I remember being around the Cosmos(?) monoblocks from Kora.  Beautiful sounding, if bass shy, amplifiers using 6AS7G triode output tubes.  From what I heard from their owner, he faced some idiosyncratic issues with them probably of the sort @roxy54 mentioned.  Had a chance to buy them from him cheap, and always sort of regret not doing so, as I found them something quite different than the norm.  Wish you good luck with these!
roberjerman
2,086 posts
 
My mistake about the output configuration of the Kora amps! I apologize! 
soma70 OP
45 posts
 
Thank you Trelja for your input and recommendations.

RJ apology accepted! 😄
soma70 OP
45 posts
 
I have seen a review for a Kora Explorer 150 SB (tube integrated) which is self biasing and so I am thinking that “SB” stands for self biasing and would apply to these mono blocks as well. I have asked the dealer to confirm via the engineer.
steakster
720 posts
 
I had a Kora Eclipse preamp for years. Loved it. Unfortunately, it was stolen from a storage locker during a move. I’m not familiar with their amps. I would suspect that they sound very nice - if matched correctly with the right speakers.

My Kora Eclipse was driving push/pull monoblocks (a different manufacturer) using the 6C33C tubes. Great match! There are many trustworthy sellers of those tubes on Ebay. Allow a month or so for standard delivery from Russia or Ukraine. I also purchased spare sockets from China. They were replaced twice over 12 years due to the heat. Depending on how high the bias is set, the little metal spring clamps that grasp the tube pins, will deteriorate over time. Not only does the metal char, but the spring tension relaxes. At 100 watts/ch, I suspect that the bias is fairly high. Many push/pull amps using the 6C33C tubes are in the neighborhood of 35-50 watts/ch. Also, the wiring to the sockets might need to be replaced as well. Replacement of those parts is simple. The main problem is that the manufacturer in France never supported any of their products. There is only one technician in the U.S. that Kora certified. Getting a hold of the schematics would be extremely helpful for any future repairs.

Here’s a picture of the 6C33C used in the guidance system of a MIG jet fighter - it’s original purpose.
https://www.google.com/search?q=6c33c+in+guidance&client=firefox-b-1&tbm=isch&source=iu&...:
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