Originally designed for use in televisions and radios, 6CS7 tubes generally see little use in audio applications. The chief designer and owner of Leben Hi-Fi Stereo Company, Mr. Taku Hyodo, who is often referred as one of the eight best tube amplifier designers in Japan, has a fondness for the 6CS7 type, presumably because of its high degree of linearity and very robust design – and very low prices 20 to 30 years ago.
Also see: Kasper Bergholt Photography, Copenhagen
From TVs & Radios to high-end Japanese HiFi
In addition to the Leben CS-600 (integrated tube amplifier) & the Leben CS-600P (power amplifier), 6CS7 tubes are also used in non-Leben products such as the SRA-3S headphone amplifier by Stax, the American General Electrics RIAA UPX-003A from the beginning of the 70s and the 5B7 Bassman guitar amplifier from American producer Fender in addition to a range of do-it-yourselves designs.
Applications of the 6CS7 tube (Sylvania datasheet)
“Sylvania 6CS7 and 8CS7 are miniature, double triodes having dissimilar sections; section 1 is intended for operation as a vertical deflection and oscillator and section 2 as a vertical deflection amplifier. The 6CS7 and 8CS7 corporate controlled heater warm-up time to ensure dependable operation in television receivers employing a series heater string”.
Four 6CS7 in the right-hand side of a Japanese tube amplifier from Leben Hi-Fi Stereo Company.
Construction of the 6CS7 tube (Sylvania)
Basic information on the 6CS7
Base: E9-1, Small Button, 9-Pin
Outline: 6-3
Basing: 9EF
Cathode: Coated Unipotentiale
Heater warm-up time: 11 seconds
Triode 1
Plate voltage: 250
grid voltage -8,5 volt
Plate current 10,5 Ma
Transconductance 2200 mikro-ohm
Plate resistance 7750 mikro-ohm
Triode 2
Plate voltage: 250
Grid voltage -10,5 volt
Plate current 19 Ma
Transconductance 4500 mikro-ohm
Plate resistance 3450 mikro-ohm
Triode connections in the 6CS7 tube
Triode 1 connects pins 6, 7 and 8.
Triode 2 connects to pins 1, 3 & 9.
How big / large are 6CS7 tubes?
The 6CS7 tube is fairly large compared to for example the ECC81 or the 6AK5, which often seen in preamplification circuits. Here’s an example showing a Tung-Sol 6CS7 tube, a 6190 (12AU7WA) and a General Electric 6AK5 (5654).
Prices on a par with the ECC88, ECC82 and ECC81
As of 2024, the prices are on a par with some of the best NOS (New Old stock) ECC82s tubes from Telefunken, Siemens Halske, Valvo, Amperex, Tung-Sol, Sylvania, high-end modernly produced tubes from for example the Genalax Gold Lion series.
6CS7 in Stax, General Electrics and Fender
Supplies of 6CS7 tubes have dried up lately
The supply of NOS (New Old Stock) 6CS7 tubes has quickly depleted during the last couple of years. “The Tube Store”, the American reseller of vacuum tubes has addressed this issue on their website, providing a notice stating that their supply is extremely limited in comparison to earlier, and as a result they are no longer able to offer matched pairs or quads of 6CS7s:
“Note to Leben [CS-600] amplifier owners, we do not have matched sets at this time. These tubes are very difficult to find. Only odds and ends of various brands available,” The Tube Store, August, 2023.
In general this phenomenon is called “Vacuum Tube Extinction” and is something one should be aware of when investing in a tube amplifier.
Substitutes for the 6CS7: ECC81 or ECC82?
The last 6CS7 tubes were, to my knowledge, produced in the late 80s – in contrast to for example the ECC81 (12AT7) and the ECC82 12AU7) tubes that are in current production because there’s a market for them for both in old Hi-Fi equipment and in new designs in a wide range of RIAAs, preamplifiers and amplifiers.
Incoming tubes: Black plate, O-getter, Marconi
Matched quad of GE (General Electric) Canada, black-plate, O-getter marked Marconi from the early 60s are on their way to me from Canada. Some of the tubes are re-branded as ‘Admiral’, but the construction of all the tubes is the same.
They’ve been tested by a professional on a Hickok 600A tube tester with the following measurements:
Tube 1 – 2300 4850;
Tube 2 – 2325 4800;
Tube 3 – 2275 4750;
Tube 4 – 2350 4800;
New Old Stock value are: 2200/4500.
Also see:
Objects for an Ideal Home
6X5GT Tubes in the Leben RS30-EQ RIAA
Photographer in Copenhagen