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