SMALL ex USSR PENTODES FOR GREAT SOUND

The USSR produced several types of small 7 pin pentodes that provide excellent results when used in high quality audio amplifiers.

In the west, engineers know very little about these valves and many people find it hard to believe that a 10 cent valve can sound better than an ECC 81, 82, 83, 85. It seems unbelievable but it is true. 

It is often mistakenly believed that 6J1P (6Ж1П) is a full analog of EF95 / 6F32 / 6AK5 and 6J2P (6Ж2П) is an analog of 6AS6/ 5725/ 6F36 but it is not quite true. Really Soviet vintage valves are very similar in parameters to western analogs but Soviet valves are very different in sound!

The next surprise is the longevity of 6J1P (6J2P). I know of cases when 6J1P (6J2P) worked in devices 10-15 years daily and did not change its electrical parameters during this time. But don't forget that if you use vintage valves that have never been in operation before, the vacuum inside the cylinder will be restored only after several hours or even days. And only then the electrical parameters of the valve will stabilize and you will be able to hear a sound that will surely please you.

But all the information that will be written below refers only to vintage valves from the USSR and has nothing to do with modern Chinese 6J1 valves. 

These little 6J1P and 6J2P valves are very similar, but the 6J2P has a thicker 3-grid and the lead of the third grid (pin 7) is not connected to the cathode (pin 2 )

In order for you to use these valves in the same socket connect pins 2 and 7 to each other on the socket or PCB.

For high quality amplification, the 6J1P (6J2P) pentodes are used in triode mode.

Optimal modes to achieve good excellent linear sound for triode mode were suggested by engineer Manakov.

(see below) 

TYPICAL OPTIMAL MODE 1

U=250V, Ra=47kOhm, Rk=620 Ohm, Uin=~1V. Harmonics =0,7-1%

    6J1P 6J2P      

    Ua=85V Ua=94V       

    Uk=2V Uk=1,95V  

    Uout=27V Uout=26V  

TYPICAL OPTIMAL MODE 2

 U=250V, Ra=12kOhm, Rk=220 Ohm, Uin=~1V. Harmonics =0,25-0,4%

    6J1P 6J2P      

    Ua=126V Ua=139V   

    Uk=2,2V Uk=2V     

    Uout=23V Uout=21V  

According to many listeners the sound signature of 6J1P (6J2P) is noticeably superior to 6n8s (6SN7).

But do not forget that the plate voltage limit for these pentodes is limited to 200 volts, and for 6J1P-EV (6J2P-EV) the plate voltage limit is no more than 120V, which is much lower than the plate voltage limit of 6n8s (6SN7).

Another unusual feature of the 6J1P (6J2P) is the ability to operate at low anode voltage.

I have put a few typical low anode voltage circuits below. 

Low plate voltage is very useful if you are stating an amplifier using the Loftin White circuit (no interstage capacitors)I post an example of such a circuit below. 

These pentodes amplify the sound already at anode voltages of 12 volts and higher. Of course you will not get as high linearity as in typical (optimal) modes of use, but sometimes it is very convenient to use low anode voltage. For example, if you have a solid-state amplifier and want to have a vacuum valve pre-stage.

Also 6J1P (6J2P) are perfectly applicable in Long Tail pair splitter as a current source with low voltage drop.

Using a current source in such a Long Tail splitter allows you to further linearize the splitter and use the similar anode resistors in the splitter valves.

The 6J1P (6J2P) valves were also available with additional letters at the end of the name. (B, EV, E).

Here's what these additions mean:

B - valves of increased reliability and mechanical strength

E - valves of increased durability with a guaranteed service life of more than 5000 hours.

EV - valves with increased reliability, mechanical strength and durability.

Valves with indices at the end of the name were used only in industrial equipment of high reliability or military equipment.

It is also well known that the sound signature of valves with indexes (B, EB, E) differs for the better from the sound signature of valves without indexes.

6J1P (6J2P) were produced by several factories in the USSR.

I know the valves produced by MELZ, Svetlana, Novosibirsk and Voskhod plants.

Svetlana valves have a different design of the getter holder in the form of a ring.

The character of the sound of valves of different manufacturers also differs from each other. Valves of any manufacturer produced before the mid-70s sound "juicier" and "cleaner" than valves produced during Gorbachev's Perestroika period of the late 80s.

You can always buy 6J1P 6J2P 6J1P-EV 6J2P-EV from my Ebay store.

https://www.ebay.com/itm/174211118228

https://www.ebay.com/itm/174982871021

https://www.ebay.com/itm/174884094988

https://www.ebay.com/itm/174624392247

https://www.ebay.com/itm/174418657695

https://www.ebay.com/itm/175438387601

https://www.ebay.com/itm/174249578944

Lots with a different number of valves are available upon request.

Please read the lot descriptions carefully before ordering and if you have any questions, do not hesitate to contact me.

If you would like more information on these valves, please write in the blog comments.

At the end of this text, I am attaching datasheets for the 6J1P (6J2P) valves.