6550

Beam Tetrode — Octal

Tung-Sol

Known Equivalents & Substitutes

6550A6550BCK6550CV52207534

Similar Tubes (Not Drop-In Compatible)

7027-A

RCA lists as similar type — same Octal base but different ratings and applications

Often listed as equivalent but different max ratings (Va_max 800V vs 660V) — not a drop-in in all circuits

Electrical Specifications

Section 1 — Beam Tetrode

Absolute Maximum

Anode Voltage (max)Anode Voltage (max)660V

Screen Voltage (max)Screen Voltage (max, pentode)440V

Anode Dissipation (max)Anode Dissipation (max)42W

Screen Dissipation (max)Screen Dissipation (max, continuous)6W

Cathode Current (max)

Notes

Tung-Sol rates Pa_max at 42 W; RCA rates it at 35 W for Class A1 service. Use 35 W as the design limit for conservative Class A1 designs.
Rg_max depends on bias method: fixed bias 50 kΩ max, cathode (self) bias 250 kΩ max.
In push-pull operation, a small resistor in series with each cathode is recommended for better maintenance of balance between tubes.
Tung-Sol datasheet lists the tube as 'Pentode' but it is a beam power tube with beam-forming plates rather than a true suppressor grid. JEDEC basing 7AC.
Pin 1 is labelled 'No Connection or Base Shell' on the Tung-Sol datasheet; RCA shows pin 1 as base sleeve. Pin 6 is 'No Internal Connection' per RCA.
RCA provides triode-connection data with Vg2 connected to anode; Tung-Sol does not include triode data in their datasheet.
KT88 is often listed as an equivalent but has different maximum ratings (Va_max 800 V vs 660 V for 6550). Not a drop-in replacement in all circuits.

Pin Layout — Octal

1No Connection / Base Shell

2Heater

3Anode

4

Socket-Compatible Tubes ⚠ Not electrically compatible

References