# 6CS7 Tubes: Data, Specifications & Usage

*May 16, 2025 — Kasper Bergholt*

Originally designed for use in televisions and radios, 6CS7 tubes are rarely used in audio products. The chief designer and owner of Leben Hi-Fi Stereo Company, Mr. Taku Hyodo, who is often referred to as one of the eight best tube amplifier designers in Japan, has a fondness for the 6CS7 type, presumably because of its notably linear response and robust design – and low prices 20 to 30 years ago. 

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 Electric RIAA UPX-003A from the early 70s and the 5B7 Bassman guitar amplifier from American Fender in addition to a range of do-it-yourself designs.

			
				
			
		Two General Electric 6CS7 Tubes marked Tassa Radiofonica imported from Milan, Italy. Pentax K5 & Pentax 35mm 2.8.

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 incorporate controlled heater warm-up time to ensure dependable operation in television receivers employing a series heater string”.

			
				
			
		1950s/1960s datasheet from Sylvania on the 6CS7 tube characteristics.

Here’s a schematic of the pin layout of the 6CS7. The pins are counted looking at the bottom of the tube and counting left to right.

Also see: Copenhagen artist & photographer, Kasper Bergholt

Quad of Sylvania tubes

			
				
			
		Four Sylvania tubes – New Old stock

			
				
			
		

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 6CS7Base: E9-1, Small Button, 9-PinOutline: 6-3Basing: 9EFCathode: Coated UnipotentialHeater warm-up time: 11 seconds

Triode 1Plate voltage: 250grid voltage -8,5 voltPlate current 10,5 MaTransconductance 2200 micro-ohmPlate resistance 7750 micro-ohm

Triode 2Plate voltage: 250Grid voltage -10,5 voltPlate current 19 MaTransconductance 4500 micro-ohmPlate resistance 3450 micro-ohm

Triode connections in the 6CS7 tubeTriode 1 connects pins 6, 7 and 8.Triode 2 connects to pins 1, 3 & 9.

			
				
			
		Vintage Raytheon 6CS7 tube

How large are 6CS7 tubes?

The 6CS7 tube is fairly large, for example compared to the the ECC81 or the 6AK5, which are often seen in preamplification circuits. Here’s an example showing a Tung-Sol 6CS7 tube, a 6190 (12AU7WA) and a General Electric 6AK5 (5654).

			
				
			
		Tung-Sol 6CS7 tube next to a 12AU7WA and a General Electric 6AK5 (5654 / EF95) tube. Nikon D3 & Zeiss Milvus 50mm.

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 modern tubes from, for example, the Genalex Gold Lion series.

			
				
			
		Four NOS (New Old Stock) Sylvania 6CS7 tubes.

6CS7 in Stax, General Electric and Fender

			
				
			
		Close-up image of a vintage / NOS tube from Sylvania.

Supplies of 6CS7 tubes have dried up lately

			
				
			
		Tubes from the American manufacturer in front of their original boxes.

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 6CS7 tubes.

“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.

This phenomenon, sometimes described as ‘Vacuum Tube Extinction,’ is something one should be aware of when investing in a tube amplifier.

Market demand & bad audio karma

The only solution to the scarcity is if the market demand is high enough, creating an incentive to reproduce the tubes – examples of this could be the ECC81, the ECC82, 6SN7 and a range of widely used rectifier tubes. That was one of the reasons I decided to experiment with a Sunbuck (Kondo Audio Note) KSL-M7 clone based on two ECC81 tubes & a 5U4G/5U3C rectifier tube, which offers a lot of flexibility for experimenting with different tubes.

			
				
			
		Svetlana 1976 rectifier tube. 5U3C – equivalent with 5U4G, 5C3S, 5Z3P, VT-244 – for use in Kondo Audio Note preamplifier clone. Pentax K10D & Carl Zeiss 35mm.

The amplifier, sadly, turned out to be poorly assembled, perhaps a warning sign / bad audio karma for copying another company’s design. The ECC81s I can use with my Leben RS30-EQ RIAA, but I need to find a way to use some different tubes in the 5U3C family I got for the project, luckily not that expensive.

			
				
			
		NOS Sylvania 6cs7 tube boxes – some marked ‘Sylvania Electronic Tube’ and some ‘Sylvania – Canada – Electronic tube’. Photo in black and white – the boxes are distinctly yellow and back (Sylvania’s brand colours).

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.

			
				
			
		NOS (New Old Stock) Siemens ECC82 tube ‘synonymous’ with American 12AU7, CV4003 / 5814A. One of the most used vacuum tubes in preamplifier / driver circuits in tube amplifiers. This specific tube was used in an Audio Note M1 preamplifier from Audio Note UK.

			
				
			
		Four Sylvania NOS (New Old STock) & NIB (New In Box).

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 its way to me from Canada. Some of the tubes are re-branded as ‘Admiral’, but the construction of all the tubes is the same.

			
				
			
		Hand-written sheet of measurements of 6CS7 tubes. The measurements show the readings for each triode.

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;

For reference, NOS values are approximately 2200/4500.

			
				
			
		Four twin-triode 6CS7 (to the right in the photo) tubes and one 6CJ3 damper tube (to the left in the photo) for my Leben CS-600 amplifier.

Also see:

Kasper Bergholt – Copenhagen Artist & Photograper