Voltage Drop (typical)Tube Voltage Drop (at Ib=70 mA DC per plate)22
Notes
Indirectly heated (coated unipotential cathode) — no warm-up delay concerns for B+ application, unlike directly heated rectifiers.
Maximum ratings differ by filter type: with capacitor-input filter, max AC plate-supply voltage per plate is 325 V RMS at 70 mA; with choke-input filter, max is 450 V RMS at 70 mA. See Rating Chart I in the datasheet.
When capacitor-input filter is used, a minimum total plate-supply resistance of 525 ohms per plate is required to limit peak currents.
Heater-cathode voltage limits are asymmetric: +100 V DC / +200 V peak (heater positive), -450 V peak (heater negative). This matters for elevated heater supplies.
12X4 is electrically identical but with 12.6 V heater — developed for vibrator power supplies in car radios.
6063 is a different-rating substitute, not a direct equivalent.
Tube voltage drop is approximately 22 V at full rated current of 70 mA DC — higher than larger rectifiers like GZ34 (~15 V) but typical for miniature types.
Brans Vademecum groups 6X4 with the 6X5/EZ90 family across multiple base types.
Philips interchange guide lists EZ90 as direct replacement (CV493).
Pin Layout — B7G
1Plate 2 (Anode 2)
2No Connection
3Heater
4
Socket-Compatible Tubes ⚠ Not electrically compatible