Hello,
recently I got three such tubes, but I can't seem to find any information about them. They are signed only AB and USA.
They look like standard noval double triodes (12AX7 etc.), with screen between systems (pin 9) Heating of both systems is parallel.
Could someone tell me more about these tubes? Are they similar to ECC85 (6AQ8)?

Regards
Piotr

Do you have a tester? If it looks like a 6AQ8 and tests good as one, it very likely IS one (or a close equivalent - 6DT8 is near-identical). If you don't have a tester, see at least that it lights with 6.3V on pins 4&5. If not, try 12V (12DT8 most likely, maybe 17EW8)

Maybe you'll get lucky and it's a 6DJ8, but there are a multitude of tubes it could be... If it lights as expected on 6.3v, I'd measure heater current to try to narrow down the type...

http://www.nj7p.org/Common/Tube/SQL/Tub ... p?base=9AJ

Post a good close up pic of it.

Hello,
sorry for a slightly late answer, but only now I had enough time to check anything.
Unfortunately I don't have tube tester (prices are horrendous!) so I've chosen the other way.
After careful examination of connections I tried to put this tube instead of ECC85 (6AQ8) in FM tuner. To my surprise radio plays exactly as with ECC85, there's no sign of excessing anode power. I will get to measurements (especially the heater current) on the weekend.
Here's also a picture.

Regards
Piotr

Looks like a 12AT7.

Pete

Me too. If it looks like a duck and quacks, ergo.

Best to gently straighten any bent pins. Do this without stressing the glass to metal seal. I put the tip of one side of needle nose pliers at the base of the pin and gently "pinch" the pin straight.

Not 12AT7. The first post mentions filament sections are in parallel with pin #9 connected to a plate between sections. This can be seen in the photo. A 12AT7 isn't made this way. Pin #9 is center tap of the filament and there isn't a plate between sections.

There are a bunch of 6 volt tubes using 9AJ basing not 9A. Some possibilities are 6AQ8, 6BC8, 6BK7, 6BQ7, 6BS8, 6BZ7, 6DJ8, 6DT8, 6JK8, 6KN8 and many more. Most of these are similar.

So I measured heater current and it's 0.4A. Many tubes has this kind of heater, so I guess without exact measuring of parameters it's not possible to definitely tell which tube it is. I carefully examined these tubes in search of any additional writing, but there's only "AB" and "USA" written on all of them...

Thank you for your kind help.

Piotr

I believe the 400ma variants 6BC8, 6BQ7, 6BS8, 6BZ7, & 6BZ8 all sub for one another... Late versions were multiple typed... On the originals, I know max voltage ratings were less on the 6BS8(and maybe 6BC8?) but other specs are similar... And yes a 6BQ7 will work in place of a 6AQ8, tried one in a Motorola AM/FM a few days ago... It did cause some shift of the osc...


I have a GE 12AV7(those are 6/12v 6BK7) that has the shield between the sections but isn't connected to anything, as the heater tap is connected to pin 9... Otherwise it looks exactly like a 6BK7, no other 12AV7 I have has the internal shield...


Tom

AB could mean Allen-Bradley. I don't know that they manufactured vacuum tubes but they have always been into control systems and process automation.