Mystery Green Mazda valve numbers,

[boater sam]

No, gray metallising with faded green print, MO base with 7 pins, SP61 shape bulb, large top cap. I know the green battery valve you refer to, these are possibly 0.2A series heater chain valves.

[Geordie McBoyne]

Yes I've seen Mazda octal valves with grey metallising and green print and the green paint was always faint.   You could be right the valve under discussion could be one of the MO 0.2amp heater range.
Just checked the 4volt Mazda octal valves in the RGD 1046G radiogram and all have black print on them.

Geordie McBoyne.

[Mike Watterson]

You CAN fit a frequency changer on seven pins (not just Octodes, Heptodes)
I'd connect to a PSU monitor current & voltage and see what looks likely, or multiply cold resistance by x2 for approximate.


X78 is Triode - Hexode in a 7 pin base! even with Indirect heater!
http://www.radiomuseum.org/tubes/tube_x78.html

[pwdrive]

Excellent deduction, it has only 7 pins, so its unlikely to be a frequency changer, likely to be a pentode, TH233, XP41, TH41 etc.

Its not a green valve, just green printing.

If pin 7 only is missing then it will be an indirectly heated pentode:

Pins 1&8 = h&h

Pin 2 = k

Pin 3 = a

Pin 4 = g2

Pin 5 = g3

Pin 6 = Met.

TC = g1

I have details of all the pin outs for MO's.

Lawrence.

[pwdrive]

Ref. post #14, choices are:

SP41
SP42
SP181
V453
VP41
VP133

Pin outs as in post #14.

Those can be narrowed down by roughly determining the heater voltage and possibly current.

Lawrence.

[boater sam]

Nicely done Lawrence, that narrows it down a lot. A few minutes on the tester with an ammeter in the heater will narrow it further. Thank you.
That green printing is almost invisible, tried wetting, washing, UV without any success.

[pwdrive]

Mazda octal valve base pin outs.

Source: Radio Valve Data, 8th edition, Iliffe:

       

Lawrence.

[Herald1360]

Had a bit of a play in GIMP.

Maybe a good brightly lit high res starting picture would work even better. The right hand valve could do with being rotated about 60deg towards the pencil.

[Mike Watterson]

If your name was Jackson Pollack or some such, that would be worth millions

[boater sam]

Photo is super definition mode, with 24w LED lighting, believe me, even with a magnifying glass in daylight there is nothing  discernable at all.
Under other artificial lighting it disappears completely, I couldn't see where the print was hence the off center orientation.

No, I'm not a pollock, just a crumbly. 

I will work it out from the pin out, heater current and on the tester to find the grid/s. Only thing is I have dozens of these to ID.