Any suggestion for a 7 pin substitute to the 6J6 tube ?

[kagliostro]

My project to build a whole 7 pin amp momentarily stops

http://www.bensykora.com/7cylinder/7cylinder_final.gif



today I give a try with my tube tester to the two 6J6A and 6J6WA I've in stock

the 6J6A has a 25% - 80% efficency (may be used)

and the 6J6WA has a 25% - 40% efficency (looks really as new)

may be the problem is that my tube tester has only a setting for 6J6 tubes and not 6J6A & 6J6WA

but I doubt the problem is this (however the triodes has a very different rating on my tubes)

http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6J6

http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6J6A

http://www.tubecollector.org/cv4031.htm

so, the next week there is a big electronics fair and I'll go on searching for other 6J6

The question is, is possible to look also for other 7 pin tubes for the purpose of a LTPI like in the schematic I posted ?

May be I'm lucky and I find some 6J6, but I would like to give me further chances for a successful search

Any council ?

Thanks

K

[PRR]

> only a setting for 6J6 tubes and not 6J6A & 6J6WA

The "A" can mean any change, but nearly ALL "A" tubes are "controlled heater". The heater wire gauge is standardized so that heaters may be run in series without unbalanced warm-up.

The "W" is a "highly reliable" version.

So for basic testing, these are all the same.

> 80% efficency

Don't know what that means.

But note that many "tube testers" test a MAXimum current. 6J6 is a 9mA tube. In audio we don't work it so hard; your plan looks like 2mA. So the tube could be way-short of 9mA yet still work great in that circuit.

[kagliostro]

Thanks for the explanations PRR

I don't know how much my tube tester can be precise

but what really I find disheartening is one triode is 25% efficiency and the other in the WA tube is 40% and in the A tube is 80%

If I've to use one triode of the tube for a gain stage and the other for a concertina, I think all will be different

but I want to use it in a LTPI, didn't a so relevant difference in efficiency between the two triodes sort in an unbalanced signal coming out from the PI  with negative effect on the sound ?

K

[DummyLoad]

base is 7BF - look for other tubes with same base.
ref. RCA RC-30 receiving tubes manual.
http://www.tubebooks.org/tube_data.htm

ECC91 = 6J6A
http://tubedata.milbert.com/sheets/154/e/ECC91.pdf

5844
http://tubedata.milbert.com/sheets/137/5/5844.pdf

5964
http://tubedata.milbert.com/sheets/137/5/5964.pdf

ECC91 & 5964 are 6J6  the other is close enough to work in your circuit.

regards k,

--pete

[PRR]

> I want to use it in a LTPI

The plan you posted is not a LTP. The "long tail" is short (only 1K) and bypassed. This is a paraphase. Look at the 330K resistors. V2b is forced to "unity gain inverting". It can be very sad and still do a gain of -1.

Build it. It will work. If V2b is dead, the amp will work at lower output power... you can play it while waiting for a better 6J6 to find you.