First tube photo in a while: A Russian 5U3C (Russian/Cyrillic: 5Ц3C) rectifier tube from 1976, so-called New Old Stock (NOS), meaning that the tube has never been used. The tube was bought for a Kondo Audio Note KSL-M77 pre-amplifier clone, this is not to be confused with an official Kondo product – or a product from similarly-sound Audio Note UK.
I’ll leave thoughts on the ethical aspects of the project for another blogpost.
As described in a previous post, I’m very satisfied with my Leben CS-600 integrated amplifier, but there should always be room for experimentation. What drove me the the KSL-M77 clone was 1) wanting to use a minimalistic preamplifier with only one function – amplification & a volume knob. No bass or treble boosts, no reverse function, only one output and one input and no tape in our out functions – combined with a pathway as short as possible.
In addition, I’d like to combine tube-based preamplification with solid state power amplification, to add more watts to my Harbeth M30’s. The CS-600 “only” produced 32 watts configured with 6L6GC/5811 output tubes – or 28 watts with EL34 output tubes (the amplifier support multiple tubes through to two switches).
Two ECC81 driver tubes & 5U3C/5U4G rectifier tube
The KSL-M77 pre-amplifier is based on two ECC81/6201/CV4024 driver tubes fed by a single 5U3C-family tube (5U4G, VT-244, 5Z3P)
I got two matched rectifier tubes on eBay, which is a new principle – when needing one, I get two for future use, as supplies are drying up for a lot of these classic tubes (produced before, let’s say, the 80s) that find use in a lot of different designs / configurations (other types of tubes see so little use that no new ones will ever be produced, presumably, such as the 6CS7 variety.
1976s Svetlana Winged-C 5U3C
This specific 5U3C was manufactured in 1976 and marked with the text OTK-1 (Отдел Технического Контроля), which means the tube has undergone and passed quality control before leaving the Svetlana factory. The OTK stamp was a common quality control mark on Soviet electronic components, especially those intended for military or industrial use.
About the Kondo Audio Note KSL-M77
The current Kondo Audio Note KSL-M77, where KSL presumably stands for Kondo Sound Labs, and the ‘M’ for either mains or Meister, is based on a single 6X4 rectifier tube (which is a lot smaller than the 5U3C) and eight 12AU7 driver tubes.
Judging by weight
Weight can be a good parameter to evaluate an amplifier design by. The original current-production KSl-M77 weighs in 17 kilos, whereas the clone weighs around 4 kilos, eliminating any doubt as to whether the components and design are in any way close to each other.
Differences between the original and the clone
However, it differs from the original in that it lacks multiple inputs or a built-in phone stage for turntables, in addition to the number and type of tubes. The Kondo Audio Note is based on a 6X4 rectifier tube and eight 12AY7 tubes.
Tubes compared to camera lenses
Some people choose their amplifiers based on which tubes they prefer the sound of, much like photographers select their cameras based on the lenses they already own.
I’ll follow up with either a new post or an elaboration of this one, once I’ve experimented with the KSL-M77 clone.
