KT88 vs 6550
KT88 versus 6550 — two tetrodes compared.
KT88 vs 6550: which one to choose?
The KT88 and 6550 are directly equivalent in most applications — same pinout, same electrical envelope, same general sonic signature. KT88 is the American/RETMA designation; 6550 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 | KT88 | 6550 |
|---|---|---|
| Full name | KT88 | 6550 |
| Type | Tetrode | Tetrode |
| Primary use | Power (PP) | Power (PP) |
| Era | 1956 | 1955 |
| Heating | indirect | indirect |
| Heater voltage | 6.3 V | 6.3 V |
| Heater current | 1.6 A | 1.6 A |
| Amplification factor (μ) | — | — |
| Transconductance (gm) | 11.5 mA/V | 11 mA/V |
| Plate resistance (rp) | — | — |
| Max plate voltage | 800 V | 600 V |
| Max plate dissipation | 35 W | 42 W |
| Base | octal | octal |
| Manufacturer | GEC | Tung-Sol·GE |
| Rarity | Sought-after | Common |
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 KT88 vs 6550 in the interactive comparator →