A very rare GEC 12AT7 B309 (ECC81) pre-amp tube testing significantly above the specification of a new tube. It arrived wrapped in its box, and the label was stuck to the cardboard wrap (apparently a common issue for this type of label).
It has black 4-hole welded plates and a square getter.
Extremely rare in NOS condition, with original GEC foil badge and Osram BVA box. This is a genuine GEC tube (GEC owned the MOV Marconi Osram brand), and is NOT a re-badged Mullard which was common for later valves.
It has been tested on an Avo Mk3 Valve Tester which can determine both plate current (mA) and transconductance (mA/V). and it tests extremely strong and balanced (the GM on one is a bit of an outlier, but not an issue for a pre-amp tube).
Even NOS valves can have hidden faults, so I personally test every tube. The final photo shows this valve under test for transconductance.
| Measurement | Data Book Specification |
Triode 1 | Triode 2 |
|---|---|---|---|
| Plate Current: ia (mA) | 10 | 14 | 14 |
| Transconductance: GM (mA/V) | 5.5 | 6.5 | 5.5 |
