Hi all,
The below link is a pic of what obviously looks like a 6A7, but there's no top cap and the heater is on 2 + 7, not 1 + 8
If anyone can help, would be appreciated.
Cheers,
Bob

Image Link

Took a look over at
http://www.mif.pg.gda.pl/homepages/frank/vs.html
to see maybe that A is a cyrillic symbol, but it turns out that their A is the same as our A. Idea being that it was a Russian tube. Doesn't look it now.

Another thought, that your tube has no top hat and has an octal base, that it might be a prototype for the 6SA7. But the pinout is somewhat different from a 6A8, and definitely different from a true 6A7. If your tube were a glass base like a miniature 7 or 9 pin, you could figure out which pin feeds what grid, cathode, plate and so on. Can't really tell with a metal, except with a tube tester should be able to tell you which is the cathode, and grid one. And of course the heater with a VOM.

The original RCA metal valves had 6A8 & 6L7 as mixers. Both had top caps, see
http://www.mobileers.com/chiTechhelp.htm, RCA metal tubes pdf
A bit of a mystery. Does it have any brand name?

PS: Stokes "70 years of radio tubes & valves" has a picture of one of these reported as Russian but makes no comments about its function.
The other marking is date of manufacture. They can be marked with the brand name of the western distributor. A picture of a 6K7 has Trigon on it , a British distributor.

Hi crew,
Thanks for you input.
The only other markings I can find are as per below pic links.
A 'K' in a circle and '30' next to it.
On the end of the base spigot is a 'P'

Yes, I did wonder about the shape of the A. I tried R, it has the heaters on the right pins, but still has a top cap for g1.

Will try some settings on the tester to see if I can figure it out.

Image Link

Image Link

Ok, I'm getting a sensible response from the tester [AVO CT-160] with the following connections and voltages

pin
1 - shield
2 - h
3 - n/c
4 - a
5 - g1
6 - c
7 - h
8 - n/c

volts
h - 6.3
g1 - -3
a - 100

With these settings, I get an anode current of 8ma and 2 ma/v gm

The anode current responds in a typical manner to a change in g1 volts

I looked through the basing diagrams of most everything made in the USA, and yours doesn't match anything.

Hmmm...the plot thickens.
Bear in mind that for those pins that I have n/c next to, simply means that I haven't yet determined if there is an electrode connected to it.

Is it possible to unpick the can off these valves?

Have determined that pin 1 is connected to the can.
Have edited my post above.

Will attempt some more measurements.

The steel can is the vacuum containment so can't be taken off without ruining it. If there is any rust it is as well to treat it with rust converter so it doesn't pin-hole and lose the vacuum.

Here is a radiomuseum link for this tube - a slightly different shape (crimped around the top rather than tophat) but with the pentagon and shows the pin-outs. Says it is like the 6SA7 as proposed by Wa2ise

http://www.radiomuseum.org/tubes/tube_6a7~2.html

1 - s (shield?) G5
2 - H
3 - P
4 - G2 G4
5 - G1
6 - K
7 - H
8 - G3

You could try the tube in a radio in its 6SA7 socket to see if it works. Trying to think of any scenario where the radio or tube could get damaged, can't think of one but that doesn't mean that one doesn't exist! Maybe test it in a radio that has a phono or such switch that turns off the B+ to the tube but still heats the heater. Turn the radio on with the tube in the 6SA7 socket, with the radio switched to phono. Once the radio tube heaters are hot, try switching to "radio" and see if you get reception. Have the radio tuned to a strong station near the bottom of the MW band beforehand, using the radio's 6SA7. That way, you should hear the station at least only partially off tune, with the tube under test. If it is really a 6SA7. If not, you can quickly bail out, by switching back to phono. Be sure it's not a dirty switch.

That looks like it may be it.
I did look over radiomuseum's web but missed that variation of the 6a7.
Don't have a radio that uses a 6sa7, but will hook it up to the tester and try again when I put it back together - in the middle of a re-calibration atm.
Thanks guys

V 55 is also an electron tube number.

Pins 2&7 are the conventional octal heater pinouts Filament rectifiers 2& 8
Pin 3 Most common plate pin
Pin 8 Most common cathode pin

6A7 is a 7pin valve & this one is IO (8) V numbers were used by British air force. It could be also a NATO number. Its a toss up if that is Cyrillic and that symbol (D) actually means Metal type.

Although the shield may effect, try running a magnetic compass around it.

This may well be an oscillator valve, only it might be a klystron?

Marc