Please help identify this tube

[egmac5]

A friend found this gem in their garage. The only marking is on the inner support marked "Y-85-Hi". There are 4 contacts on the bottom (two for filament, two NC). Plate contact on top and cathode (I believe). Would like the specs on this if possible.

[Ty_Bower]

I stared at http://www.tubecollector.org/index.shtml for a long while, but didn't see anything that matched. It seems to me it should be some flavor of direct heated triode, with the filament connections on the bottom, plate out the top and grid on the side.

[EWBrown]

The "Y" labelled tube numbers were often assigned to prototype tubes, or those in early stages of development.

What is the overall height of the tube, and max diameter of the spherical section? That may help to ID this mystery...

/ed B

[egmac5]

I initially tested the filament and thought there was continuity, however, that was caused by a loose ring on the stem assembly shorting the filament conductors. Real bummer This tube was more likely a triod transmitter for Ham radio in the 50's Britton


Marconi-Osram British system

The Marconi-Osram designation uses a single letter followed by two numerals and sometimes by a second letter identifying different versions of a particular type. This British system dates from the 1920s.
The letters generally denote the type, (diode, triode, pentode, etc.), or use, (frequency-changer, I.F. amplifier, detector, etc.), of the device and the numbers are issued sequentially for each new device.
Examples
L63 = Triode similar to one half of a 6SN7
U14 = 5AS4
Y61 = 6U5G
X61 = 6J8G[/color]
Z77 = 6AM6 = EF91

We will most likely drill a hole in the ceramic bottom and place a LED to light it up as a display piece.

Thank you for your investigation,

Ethan

[20to20]

QSL.JPG (327.84 KiB) Viewed 2006 times

It's tough to tell, scale-wise, if this is the same tube. But it may lead to something. 100TH

Edit: After closer looks it's obvious that this one is less substantial in many places.

HTH

[Geek]

With the fins.... I'm thinking 250TH maybe?

[Ty_Bower]

I'd say that's a very good guess.

http://www.radiomuseum.org/tubes/tube_250th.html