THE 7189,  7189A,  &  EL84/6BQ5 POWER PENTODES

7189 versus EL84/6BQ5

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 volt range.

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.


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.  Click here for tube pinout diagrams.

If you like, have a professional measure the plate voltages in your amp, especially if you're blowing out non-industrial tubes.

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