Frame-grid construction gives very high transconductance (~25 mA/V at typical operating point), making it one of the highest-gm small-signal pentodes available.
The E180F/6688 is a Philips/Amperex design widely used in professional audio and instrumentation. The Soviet 6J9P is the direct copy.
Used extensively in Soviet oscilloscope vertical amplifiers and wide-band IF stages.
Can be triode-strapped for audio applications — provides very high transconductance as a triode.
Pin Layout — Noval
1Grid 3 (Suppressor)
2Anode
3Cathode
Socket-Compatible Tubes ⚠ Not electrically compatible