Dual low-noise triode.
Dual low-noise triode.
The 4BZ7 is a miniature 9-pin (Noval) high-transconductance, semi-remote-cutoff dual triode constructed in a T5½ envelope, specifically optimized for VHF cascode amplifier applications but increasingly adopted in high-linearity audio designs. Functionally identical to the 6BZ7 except for its heater architecture, it is designed for series-string operation requiring a 4.2 V AC/DC supply drawing a 600 mA bogey current, featuring a controlled 11-second warm-up cycle. At a standard operating point of 150 V on the plate with a -2 V grid bias, each symmetric triode section exhibits an amplification factor (\(\mu \)) of 36, a transconductance (\(g_{m}\)) of 6,800 \(\mu\mho\) (6.8 mA/V), and an internal plate resistance (\(r_{p}\)) of 5,300 ohms. The structural geometry includes an internal shield connected to pin 9 to isolate the sections, suppressing inter-unit capacitive crosstalk and yielding an ultra-low direct grid-to-plate capacitance (\(C_{gp}\)) of just 1.1 pF per section. Boasting a maximum plate dissipation rating of 2.0 Watts per plate and a high heater-to-cathode voltage rating (\(V_{hk}\)) of 200 V (with cathode negative), the 4BZ7 is highly resilient against cathode-follower stress and is leveraged by audio engineers as a rugged, high-current alternative to the 6DJ8/ECC88 for low-noise preamplifier input and driver stages.
