12BH7A Sylvania, short grey plate, round getter

Description

12BH7A made by Sylvania USA

These tubes are in great condition and feature short grey plates and round getters. These are made most likely in the 1970ies.

These are cleaned and (kind of poorly) reprinted pulls from military spare gear that was sitting around for ages and gathering dust.

No burn marks from real use or stains in the glass. All tubes test 100%+ in terms of mutual conductance and mostly very balanced with close values between triode systems.

All tubes are tested and guaranteed.

Higly regarded tubes for audio and studio applications.

General Description

The 12BH7A is a medium-gain dual triode vacuum tube that is widely used in both audio and industrial applications due to its linear characteristics, durability, and relatively high current-handling capability.

1. Audio Applications

The 12BH7A is particularly popular in high-fidelity (hi-fi) audio and guitar amplifiers, where clean signal amplification and dynamic range are important. Its moderate amplification factor (μ ≈ 17) and relatively low plate resistance make it suitable for:

• Driver stages: Especially in push-pull tube power amps, where it can drive output tubes like EL34, 6L6, or KT88 with sufficient current and headroom.

• Phase inverters: Often used in long-tailed pair (LTP) phase inverter circuits due to its balanced characteristics.

• Preamp stages: Less commonly than 12AX7 or 12AU7, but it can be used when more current drive is needed.

Compared to a 12AX7 or 12AU7, the 12BH7A delivers more current, making it better suited for driving capacitance-heavy loads or long cable runs in audio circuits.

2. Industrial and Laboratory Equipment

The 12BH7A was also used in test equipment, oscilloscopes, and signal processing gear, especially in the mid-20th century. Its rugged construction and stable operation under continuous use made it ideal for these applications.

• Used in analog computers, function generators, and measuring devices

• Common in military and aerospace electronics during the tube era

3. Comparison to Other Tubes

The 12BH7A is often compared to the 12AU7 (ECC82), but it handles more current, has a higher power dissipation, and offers better linearity in certain operating conditions. It’s also sometimes replaced with the ECC99 in hi-fi designs, though they are not strictly interchangeable.

Key Technical Data (Per Triode Section)

Construction Features

• Glass envelope, miniature 9-pin base (B9A)

• Designed for greater reliability and ruggedness

• Suffix “A” indicates a controlled heater warm-up characteristic (ideal for series heater chains)