Today's market price of vintage 12AX7/ECC83 tubes is very high. Let's analyze whether 6n2p tubes can be used as an inexpensive replacement for 12AX7/ECC83.
I do not write here about Chinese 6n2 tubes and consider only vintage 6n2p tubes made in the USSR in 1950, 60, 70, 80 and 90s.
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Did you know that the USSR did not produce analogs of Western 12AX7/ECC83/ tubes?
⁷777⁷8The answer to this riddle turned out to be unexpectedly simple. As one of the old Soviet tube designers wrote in his memoirs, the USSR could not produce a rigid 12 volt heater filament of the same thickness. (In the 12AX7/ECC83 tubes, each triode inside the cylinder has a 6 volt heater and the two heater filaments are connected in series.)
In the USSR When trying to assemble a 12 volt heater line at a mass production plant, engineers encountered a problem where one triode in the cylinder had an “overheated” cathode and the second triode in the cylinder had a "cool" cathode.
The way out of this situation was to connect the 2 heater filaments in parallel. This technical solution had several advantages, the main of which was compatibility with the 6 volt line heater of other tubes in the amplifier (TV, amplifier, appliance) and the possibility of using one 6 volt transformer winding to supply the driver and output tubes.
As is well known, the 6n2p tube has very close parameters with the 12AX7/ECC83, but differs with a 6 volt heater and slightly lower gain. You can use the 6n2p in approximately the same modes as the 12AX7/ECC83. But the lowest level of odd harmonics in the 6n2p tube is achieved at 1.4 -1.8 volt bias. In this case, the level of the 2nd harmonic will be about - 30 dB, the level of the 3rd harmonic less than -60 dB
In the USSR 6n2p tubes were produced at 2 factories Reflektor (Saratov) and Voskhod (Kaluga).
Reflektor factory logo (triode picture). Logo of Voskhod factory (Raketa). In the early version, the Raketa logo is much larger in size.
I have rarely come across tubes made in the 50's at Foton (Tashkent) - Rhombus logo and Tantal (Saratov) with the old factory logo in the form of a hexagon. But you are unlikely to find such tubes on sale. Photo of rare tubes below:
A common criterion for assessing the sound quality of tubes is the date of their production. In the USSR, tubes made in 1950-60 do sound better than newer ones. But if tubes made in the early or mid 70's sound very good, and sometimes just like their older brothers from the 60's, tubes made in the 80's always sound worse.
But besides the years of production, the sound quality of 6n2p depends on their design. The 6n2p tubes were produced in several different designs and these tubes sound completely different.
The first design is the tubes in the picture below.
These are the simplest sounding tubes, can have a wide range of parameters of halves and I recommend using them only in 2 cases:
1) when budgets are very limited
2) when used in guitar amplifiers.
Tubes of this design sound rather stiff with characteristic metallic notes of transistor amplifiers. But sometimes you may even like this sound!
There is one modification of these tubes with stiffening ribs on the anode. This is an early 6n2p design that sounds better, but nevertheless this tube is not as good as the ones described below.
I sell 6n2p tubes in lots, 4, 6, 8, 16, 32 pcs each. Please look at these links and find what you need.
https://www.ebay.com/itm/175640519099
https://www.ebay.com/itm/174217820551
https://www.ebay.com/itm/175438349467
https://www.ebay.com/itm/174816851141
https://www.ebay.com/itm/174348054264
You can also order used 6n2p tubes from my store without hesitation. I test each tube and the parameters of used tubes are within factory tolerances on 6n2p. Buying used tubes is a great solution if you are on a tight budget.
I show listings with different numbers of used 6n2p tubes below:
(16pcs, 32pcs)
https://www.ebay.com/itm/175734984249
https://www.ebay.com/itm/174822635337
Another 6n2p tube design is visually very different from the 6n2p regular tube. Inside the cylinder you can see 2 horizontal mica plates (caps) over the anodes and silver coated anodes. These tubes sound much better than the regular 6n2p tubes. The gain of tubes with silver anodes is also slightly higher than conventional 6n2p tubes. The name 6n2p, 6n2p-B, 6n2p-E. 6n2p-E. Regardless of the name, these are exactly the same tubes. Tubes with indices B and E at the end of the name according to the manufacturer's specification have increased durability, but it is hardly possible to check this statement today. The 6n2p tube has a life of over 5 000 hours and a low price, so there is little need for extended life tubes.
Such tubes are produced in the 50's and 60's and I have not specifically investigated their sound, but the S and anode current of these tubes are the same as those with silver anode tubes. There are also other rare 6n2p designs. For example with silver anodes but without top mica caps.
See photo of these rare designs below:
See lots of 6pcs and 16pcs tubes below:
https://www.ebay.com/itm/174822645694
https://www.ebay.com/itm/174915591250
In 1970, the USSR changed the state standard for tube labeling. Tubes with silver anode began to be labeled as 6n2p-EV. This is the long-lasting and most publicized version of the 6n2p design. In the first years, the internal design of these tubes completely coincided with the design of tubes described above. But then one of the plates (covers) from mica began to make a smaller diameter. I put on the photo 2 types of these tubes of different years of production.
6n2p-EV tubes are more expensive than 6n2p tubes with silver anode, but the sound of these tubes is approximately the same.
You can buy 6n2p-EV from me in lots of 10 pcs.
https://www.ebay.com/itm/174668809470
Below I put some circuit diagrams of 6n2p tubes and datasheet for 6n2p and 6n2p-EV tubes in Russian. (note that the manufacturer allows a very large variation of S !!!)
Conclusion
To use 6n2p instead of 12AX7/ECC83 you will need to adapter the heater to the 6 volt line or use a Chinese adapter bought on Ebay for 1 or 2 USD.
If you have any questions about using 6n2p tubes, please post me in the comments.
Also, you can buy a variety of vintage tubes from the USSR and not only in my Ebay store.
https://www.ebay.com/str/kievchurchshop
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