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I'm planning to order an accutronics type 9 reverb from the states (im in australia) and was wondering since im getting one if i should order a type four aswell but is it possible to put two tanks in one amp? i know i have the space but for wiring, etc. Im new to this modding thing and was just wondering if further down the track ity would even be possible. cheers.
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Alright Ozzy,
Whadderya actually trying to do? Run two tanks at once or just mount two in the chassis and swap between them? 'Bout ten years ago or so I used my second Bogen M-60A mixer as a reverb circuit "test bed" - which I shouldn't have done as the other M-60A is one of my stage amps and I should have reserved this one as a spare. But that's another tale.
Anyhoo I had several circuits set up using 12AU7s and 6CG7s where I could drive two tanks in parallel each using it's own triode, or the same tube with the sections paralleled driving one tube from the plate and another from the cathode "split load" or driving the first arrangement with the circuits in series. I also played around with driving the tanks either using transformers, cap coupled, or impedance/cathode follower coupled. Yeah, had a lot of energy then and time on my hands.
In the end I found out what I call the "point of demented returns" - that is, you'd have to be demented to pursue the subject any further - and that combining more than one tank resulted in increasing muddiness without extensive filtering which robbed circuit "sparkle." Once gone it seemed to be never regained.
But I did notice that the brighest - without harsh crash, clash, and clatter - circuit was the capacitively coupled triode circuit. While some, such as Kevin O'Conner, seem to recommend using power output tubes to cap drive tanks (primarily 'cuz Garnet Gilley did it as best I can tell) I found that a single section of "higher" power triode, 6FQ/CG7, seemed best - essentially the circuit that Ampeg used on the V-4 and other models. And there are lots of other triodes with similar characteristics most of which seemed to be made to be vertical output television tubes. Some of these have dissimilar dual triodes and the lower mu/higher powered triode should make a good reverb driver while the higher mu/lower powered triode might make a good recovery tube (but you may need more stage gain). Tubes such as a 6EA7 and 6FG7 come to mind but check the specs yourself.
Hope that helps - pop an "oil can" for me.
Rob -
"Corrections"
Hey AUS,
Hope you don't mind the AU kidding - was e-mailing some friends in NSW last night and forgot I was communicating with a new victim <grin>.
Just found my lab notes from years ago and it appears that I found some merit to using two tanks driven from the same paralleled 6CG7 "triode." One, a long tank, was cap driven from the plate and the second, a short tank, impedance cathode (follower) driven. Both of these tanks were recovered into the same 12AX7 - each tank into a grid with the plates and cathodes tied together. I varied the tank levels during recovery by feeding the output coils directly into 1 meg linear pots. Unfortunately I didn't note what specifically I liked nor do I remember so you're on your own there.
RobComment
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Would a 12DW7 work out in one of these cap-driven circuits?Originally posted by Rob Mercure View PostComment
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You can think of the 12DW7/7247 as being 1/2 each of as 12AX7 and a 12AU7 and I know that the AU half has been used as a tranny coupled reverb driver by a manufacturer with the AX section doing recovery. I've also used the AU section for cap driving with some success but not as much as the 6CG7. The tubes I was suggesting are generally higher power producing than the 12DW7 but you can try it and see.
RobComment
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