These are Westinghouse labeled tubes made in England most
likely by Mullard.
The 7189A Vacuum tube is a miniature type used as a power
amplifier in high-fidelity audio equipment. It requires a
miniature 9-contact socket.
WARNING ~ The 7189A
power pentode is the same as
the 7189 but has two pinout differences, as follows:
1. The 7189, the EL84, and the 6BQ5 tubes all reserve pin
#1 for "Internal Connection" by the tube manufacturer. A
user can't assume that pin #1 connects to any particular
tube element, or to none. Pin #1 of a 7189A tube,
however, always connects internally to pin #2
(the Control Grid). In a 6BQ5 or 7189 tube, pin #1 might
or might not connect to the control grid. I've seen old
GE 6BQ5's with pins 1 and 2 connected and I've seen
current EL84's with them unconnected.
Some vintage Magnatone amps sported 7189A tubes powered
by over 400 volts. They wired pin #1 of the socket as the
control grid, assuming it would connect to pin #2 inside
the tube. If someone installed a plain vanilla 7189, EL84
or 6BQ5 tube, the amp wouldn't work because the control
grid wouldn't get signal. This was a friendly reminder to
install the higher rated 7189A tube.
2. The 7189, EL84, and 6BQ5 tubes also reserve pin #6 for
internal connection. But inside the 7189A tube, pin #6
always connects to pin #9, the screen grid. I've never
seen a 6BQ5, an EL84, or a plain 7189 tube with pin #6
and pin #9 connected.
Some vintage Magnatone amps actually have the screen grid
voltage wired to pin #9 on one power tube socket and to
pin #6 on the other.
In a pinch, you can rewire 7189A-specific tube sockets to
accept any of the tubes under discussion. Just move any
wires going to pin #1 over to pin #2. Then move any wires
going to pin #6 over to pin #9. Do this on each of the
power tube sockets.
The 7189 industrial tube is similar to the common EL84
(European) or 6BQ5 (American) 9-pin power pentode.
But the 7189 is designed for circuits operating in the
400 volt range. The EL84/6BQ5 is designed for the 300
You can safely substitute a 7189 tube for a 6BQ5
(sound issues aside) but you might think twice about
substituting an EL84 for the beefier 7189.
If you like, have a professional measure the plate
voltages in your amp, especially if you're blowing out
Heater Voltage ................................ 6.3 V
Heater Current ............................... 0.76 A
Substitutes .......................... 6BQ5, 7189, 7189A,