Two Blackburn-built ECC33s from the same code batch, never used and each still in its own Mullard carton. All four sections read at or above nominal, with transconductance well clear of the 3.6 mA/V design figure throughout.
Uh = 6.3V | Ua = 250V | Ug1 = -4.0V
| Tube | Section | Ia (mA) | S (mA/V) | Nominal (100%) |
|---|---|---|---|---|
| Tube 1 | T1 | 9.0 | 4.1 | Ia = 9.0 S = 3.6 |
| T2 | 10.1 | 4.2 | ||
| Tube 2 | T1 | 9.0 | 4.0 | |
| T2 | 9.5 | 4.2 |
ECC33 ~ CV2821
Same octal pinout as the 6SN7GT but not a direct equivalent - the ECC33 has a higher amplification factor (35 against 20) and a lower heater current (0.4A against 0.6A). Circuit check required before substitution.
Mullard brought the ECC33 out in 1949 as a high slope, low impedance double triode with separate cathodes, intended at the time for flip-flop, scaling and computer circuits. What has kept it in demand is a combination of an amplification factor of 35, a low anode impedance and an unusually small, rigid electrode cage, which together give a stable and quiet valve well suited to voltage amplifier and phase splitter duty. Many people who have tried both prefer it to the more common ECC32 for exactly those reasons. It shares the 6SN7GT octal pinout while drawing only 0.4A of heater current against the 6SN7GT's 0.6A, and carries CV2821 in the military system. Finding one unused and boxed is not easy; finding two from the same code batch is a good deal harder.
Two unused ECC33s, both boxed, both above nominal. Buy the pair now or spend the next two years hunting the second one.
SKU: 422