I believe they had 866 rectifiers. Does anyone know the Model Number of that amplifier, and where I can get a schematic of those? They were extremely powerful amplifiers. What was the tube number of the finals?

There is nothing in the manual section of Film-Tech.

Thanks - Paul

 |  IP: Logged

Best I can remember that was a MX-20 used with a MX-24 pre-amp.

 |  IP: Logged

 |  IP: Logged

Yes, it is not such a good design. One fundamental fault in all of these that I've seen, is the time-delay for kicking in the plate power is way too short. 866 mercury-vapor rectifiers must have at least a 30-seconds MINIMUM warm-up per specs first and if you can let it have a minute, better. I'd disconnect that time-delay relay and have a manual switch on the plate xfmr, wire it so filaments must warm up first and put warning sign. If you change out the 866's to new ones you must give a 30 MINUTES minimum initial warm-up. No wonder things in that amp pop like popcorn!

All Ballantyne sound was lousy, but beautiful mechanically, which probably helped to sell it. I often felt this amp needed a bigger and more rugged output xfmr too instead of that dinky little thing. As with other theatre equipment mfrs, Ballantyne just didn't connect up with the right audio people to do their sound for them, and have better stuff inside that nice metalwork.

If you can find any and overhaul them, the Simplex XL 60-watt amp with 807 finals is a much better amp. Particularly, Change all the coupling capacitors to new and overrate to the final, @1000vdc. You can get very, very good-->excellent drive-in sound in a Simplex system by installing solar cells replacing photocell, provide DC exciter lamp power, and be sure the preamps are getting proper plate voltage and not too low, it sometimes is. Given this, exciter lamps can be run @8volts, won't burn out, speech intelligibilty will be so good you don't have to push the volume so high.