Ok, I'm a little confused here. CE Dist (AKA Antique Electronics) lists two different long Accutronics-type tanks for MM amps: 4BB2A1B and 4FB3D1B. The BB has a 150Ω input impedance and the FB is 1475Ω. Big difference!
Presumably there's a change as of a given model series. The amp in question is a 212-75 (2475-75). Reverb and phaser (although phaser is marked "tremolo"). 2x6L6, cathode-driven. Looks like the CD-3 driver board. Dead tank has an open output coil, and is marked 4FB, but I'm not sure if it's the original tank.
I might just try the EB and split the difference. :-)
Ideas, anyone?
It's only money.
Check out this page: http://amprepairparts.com/reverb_numbering.htm
It shows FB for MM amps. The lower impedance EB models might work but may overload the driver IC a bit effecting "sound quality". Don't waste your time with the 150 ohm BB models in your 2475-75. My 112-65RD has the same driver circuit and it uses the shorter 8FB tank. Good Luck. -mgriffin
I used the 4FB.
I replaced the short tank in my 115RD with a 4 series, I like the reverb a lot better!
Thanks for the replies.
Thanks, all. Input and output grounds both isolated, right? (fortunately that's utterly easy to change with the newer Asian tanks...just a solder bridge on the jack PCBs)
Which models used the BB (150R) tanks?
RD50s
According to the schematic, RD50s use 8BB2A1B tanks. http://pacair.com/mmamps3/sites/default/files/docs/1650-rd.pdf They use a 2 transistor driver instead of an IC. -mgriffin