12AX7 vs 5751
12AX7 / ECC83 versus 5751 — two triodes compared.
12AX7 vs 5751: which one to choose?
The 12AX7 and 5751 are directly equivalent in most applications — same pinout, same electrical envelope, same general sonic signature. 12AX7 is the American/RETMA designation; 5751 is the European Mullard-Philips name (or vice versa). You can swap one for the other in nearly every circuit without rebiasing, with the caveat that production-batch differences between manufacturers (Mullard vs Sylvania vs JJ vs current Russian production) often matter more than the type-number itself.
Side-by-side specifications
| Spec | 12AX7 | 5751 |
|---|---|---|
| Full name | 12AX7 / ECC83 | 5751 |
| Type | Triode | Triode |
| Primary use | Preamp | Preamp |
| Era | 1947 | 1954 |
| Heating | indirect | indirect |
| Heater voltage | 12.6 V | 12.6 V |
| Heater current | 0.15 A | 0.175 A |
| Amplification factor (μ) | 100 | 70 |
| Transconductance (gm) | 1.6 mA/V | 1.2 mA/V |
| Plate resistance (rp) | 63 kΩ | 58 kΩ |
| Max plate voltage | 300 V | 300 V |
| Max plate dissipation | 1 W | 1 W |
| Base | noval | noval |
| Manufacturer | Mullard·RCA·Telefunken | GE·Sylvania·RCA |
| Rarity | Common | Sought-after |
Sonic character
Need an interactive deep dive?
The Amperatubes comparator visualises loadlines for both tubes side-by-side, simulates the SPICE response, and lets you adjust the operating point in real time.
Open 12AX7 vs 5751 in the interactive comparator →