Tuesday, April 21, 2009

Ella W6 SEPP Tube Headphone Amplifier.

I beleive these are the first pics. of the Ella W6 SEPP Tube Heaphone Amplifier. This is another Sino based product and uses 2 x 6N2 for driver tubes and 2 x 6N6 for finals. I beleive the substitute for the 6N2 is the 6AX7 tube, if anyone knows differently then please send me an email. I do beleive there is no western equivalent for the Sino 6N6, except for Russian equvalents, but if anyone knows otherwise I would be interested to learn.

The basic specs are:

Impedance range for phones: 32 ohms to 600 ohms.
Non-distorted output power: >/= 200mW @ 300 ohms.
Max. output power: 500mW @ 300 ohms.
Distortion: /= 86dB
Frequency Range: 10Hz to 120KHz
Power Supply: 220 V AC 50Hz
Power Consumption: 70VA

Tube Rolling:

For the 6N2 it is almost damn near impossible to get hold of ay 6AX7 tubes and I am still a bit weary as to whether the 6AX7 is a direct drop in replacement even though various sources on the web have indicated that it is. Looking for this tube is like looking for a real live dinosaur or dodo.

So the next best possible thing to do with such limited tube rolling options for the 6N2 is to replace them with a matched pair of Russian 6N2P-EV from Voskhod. The 6N2P-EV (EV Designator) is said to be the top cream of the crop for 6N2P's and are premium quality which should have some difference over the existing Chinese 6N2's. The 6N2P are Double Triode Tubes, made in the Russian Voskhod factory for military equipment in the year 1987. The 6N2P (6Н2П) is very similar to the ECC83 /12AX7 but it has a slightly different pinning arrangement. These are NOS.

"6N2P Data Sheet"

The Voskhod 6N2P-EV tube data measured are:

All tubes tested at :

Ua = 250V

Ug1 = -1.5V

Test results:

S = 2.0mA/V

Ia = 2.0mA

Name 6N2P-EV
Type Double triode,hi-durable,long-life
Application LF voltage amplification
Cathode type oxide,indirect heating
Envelope glass,miniature
Mass,g 15
Filament voltage,V 6,3
Filament current,A 0,315-0,365
Anode voltage,V 250
Anode current,A 0,0014-0,0032
Anode power,W 1
Grid1 voltage,V minus 1,5
Steepness,mA/V 1,6-2,65
Reverse grid current,uA 0,05
Microphnic noise,mV 100
Gain 85-115
Socket type rsh8

As for the 6N6 tubes, this is an even bigger headache, there appears to be no western equivalents which one can choose for rolling. So staying with the Russians, I have decided to replace the Chinese 6N6 tubes with the Russian "OTK" 6N6P ( 6Н6П ) from NOVOSIBIRSK of the the year 1985, these are also military grade tubes. These are NOS.

NOVOSIBIRSK "OTK" 6N6P Tube Parameters:

Filament voltage,V 6,3
Filament current,A 0,59-0,81
Anode voltage,V 120
Anode current,A 0,02-0,04
Anode power,W 4,8
Grid1 voltage,V minus 2
Steepness,mA/V 8,1-13,9
Reverse grid current,uA 0,5
Microphnic noise,mV 100
Gain 16,0-24,0

We await the arrival of the Russian tubes. 24/04/2009: After considerable difficulty, I was able to locate and secure 1 pair of Westinghouse NOS 6AX7 tubes from the States!

Tube Adapters: 12AX7 to 6N2:

Whilst awaiting for the Russian Tubes to arrive, I have also contacted Alex Shen in Taiwan who makes tube adapters and he will be sending me a pair of 12AX7 tube to 6N2 socket tube adapters by next week similar to the ones pictured below. At first I had thought about rewiring the sockets for 12AX7 tubes, but upon review the use of such adapter will allow me great flexibility with tube rolling options, there are also a vast array of good sounding 12AX7 tubes such as the Telefunken, Siemens, Mullards etc:

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