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
Post removed 
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.
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, the amp in question uses two 6C33C-B tubes per monoblock.  And although I could be wrong, I suspect the two tubes are used in push-pull, rather than being paralleled in a single-ended configuration.

Regards,
-- Al 

A nicely restored pair of Dynaco MkIII's would be a much better (and cheaper choice). Don't believe the hype that single-ended is better than push-pull. It is not! Getting 80 watts out of a SE 6C33 is nonsense! And their future availability is questionable. Stick to the proven 6550/KT88 PP output circuit! I own a pair of rare Paoli-modded MkIII's (TAS past recommended tube amp). I wouldn't trade these for a Kora!
Thank you both for your advice and clarifications. Very much appreciated. I will pass on.
The engineer or technician should make a point of checking out the condition of the sockets for the power tubes. The 6C33C-B (and the 6C33C) run extremely hot, each tube consuming something like 75 watts or thereabouts, depending on the specific design. And my understanding is that replacement of the sockets may sometimes be necessitated by long-term exposure to the heat.

...his engineer will be renewing the MOSFET capacitors
Perhaps they meant the capacitors that are used in a MOSFET-based circuit. To be sure it’s clear, a MOSFET is a transistor, not a capacitor.

Good luck. Regards,
-- Al

I remember reading about (never hearing) the Kora amps several times, more in the foreign press. The reviews that I read were enthusiastically positive about the sound of Kora amps, but I also read a cautionary warning concerning the amps regarding the danger/difficulty of biasing them. The writer said that, like some Jadis amps, they needed to be turned over and the bottom plate removed, and that there was a real danger of electrical shock.