Quote:
Originally Posted by benman94
The situation is tricky. A NOS American made 6BQ5 will likely tolerate the higher dissipation and voltages often encountered in 7189 and 7189A amplifiers. In fact, some of the early Fisher amps pushed run of the mill 6BQ5s well beyond even the 7189 ratings with no ill effect, aside from more frequent output tube changes.
As for modern tubes, the Russian EL84s will stand up to the abuse, but the Chinese tubes will not.
NOS European tubes are another ball of wax; in general, I've found them to be much less capable of tolerating the abuse that an American 6BQ5 will take.
If you don't mind rewiring some sockets, 6GK6s great substitutes for 7189s. Most of them are internally identical to a GE 7189A.
If you're building a new amp from the ground up, my recommendation would be to skip the EL84 family altogether and use the 6CZ5. They're cheaper and they offer much lower distortion at very similar operating points.
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I know Zenith used 6GK6's as a vertical output tube. Years ago I worked on a Philco HI-FI amp that used 6CZ5's, impressive! In the late 50's, RCA used a 6CZ5 as a vert out. The next years models used a 6EM5. Some juke boxes used 6CZ5's.
The application I'm referring to is an amplifier used in a early 60's Fisher console stereo.