Hello all,
I know this question has been answered a couple times, but I have an additional wrinkle. I just bought a '68 Bassman with the 2x12 cabinet. Solid back, 29 x 38. Seems like the ET-65 with another speaker is a popular choice. So my question is, What should I put in it if I want to be able to use it for Guitar and still have it sound great for Bass?
Thanks
Peter
EASY: a pair of ET-90's!!! Go for it & don't look back ...
I'm planning to build a Blackface Bassman. Haven't decided yet between the aa864 circuit or the aa165 circuit. But, I do know I want to use a 2 x 12 cab and to use it for guitar and still have it sound great for bass.
Is the recommendation still 2 ET-90's or has there been something else developed in the past 6 1/2 years that might surpass that combo?
Not sure exactly how it works, but I think you risk blowing guitar speakers when running a bass guitar through them. I guess it depends on how hard they are pushed as much as the pressure resistance in the cab, but I don't know how to figure that. The only two 12's that are rated close to the lowest note on a bass guitar are the Reaper 55Hz and the WGS12L. Two WGS12L might sound great for a Bassman depending on a few factors. You might use the less edgy sounding circuit, preamp and/or power tubes (Tung Sol 7581A's) with WGS12L's. Maybe use a lightweight torrefied wood for the cab to spare your back.
Hmmm... It just so happens that I bought a couple of the Reaper 55's when the opportunity came up last fall. My friend in high school had a 1964 or 65 Blackface Bassman that he used with his bass and never had issues with blowing speakers. As I recall, there was usually a guitar plugged in as well and both instruments sounded fine at the sock hops! It would, however, start flubbing out if a 3rd instrument was plugged in.
The flubbing out from multiple guitars into the same amp may have had more to do with the bass causing the rectifier and/or output transformer to sag, thereby modulating over the guitar notes, rather than bottoming out the speakers. I assume Noel Redding had G12H30-55Hz in his cabs and didn't have a problem, although they didn't have a very solid punch below the rated resonance (which I recall is actually ~60Hz in the basket). The 55Hz are probably worth a try anyway. The cleaner of the circuits might be desirable in that case. You could mod it with a switch to series the first two tube stages if you want more gain. Might be nice mixing with a WGS12L for some solid bass punch and added mid clarity.
Again, the bass emphasis will be partially determined by the power tubes, as well as the rectifier and transformers. Preamp tube types make a substantial difference in terms of compression and harmonic generation where gain stages are stacked. Some 12ax7's break up more smoothly and compress less, perhaps related to plate size. I always recommend trying the JJ ECC83MG in 12ax7 stages, unless you have some other brand or specific NOS tubes you want. It's just a balanced, smooth and clear sounding tube. I wouldn't recommend the JJ ECC83S though. It can be edgy, yet dark and compresses more than I'd want for a vintage amp sound. Spiral filament 12ax7 types are not recommended for the cathode follower stage due to a low voltage rating in some part of the tube. The JJ ECC81S isn't a bad option for the 12at7 in the PI slot, unless you have something else in mind. I think it's an easy mod to change the PI to a 12ax7 (might be a good option with the AB165 circuit). The Sovtek 12ax7LPS is a common choice for Marshalls. The long plate JJ ECC803S compresses and distorts less. It generally sounds more bassy. Maybe try it first if you go 12ax7 in the PI, or use another ECC83MG.
Anyone reviewing the Tung Sol 7581A tube likes everything about it more than pretty much any current 6L6 variant. It's like a cross between a 5881 and KT66. Expensive, but very robust and should last years. The JJ 6L6GC are very bassy, but crunch hard when driven. The short bottle TAD (ShuGuang) or Tung Sol 6L6GC sound thin and a bit screechy.
I suspect you are right about the output sag. I was only 16 or 17 at the time and the last thing on my mind were the engineering challenges of amplifier circuits!
I think speaker flub would be an issue in an open-back since there's no back pressure. You could punch the speaker parameters into this enclosure calc to determine how low you want the bass response:
https://www.micka.de/en/
A vented box is probably the way to go, but I'm not sure how to deal with the port size for two speakers. Double both the box and port volume? Of course, the results would completely change with different speakers. The Reaper 55Hz should do the job for you, but you might want to add a middle knob to the tone stack. They are fairly scooped speakers. I love the sound of them though. I assume you saw this:
http://fenderguru.com/amps/bassman/
Thanks for the link for the cabinet. I haven't decided just what I'm going to use to build it. (walnut, pine, cedar, or baltic birch plywood) That choice will definitely influence the tone. I will probably use a 3 piece closed back and then play with venting it a bit at a time. If I go too far, I will only have to scrap 1 piece of the back panel. Also, I will probably start with a 20" x 32" x 11" cabinet. If I think it will benefit from more interior volume, I can easily add more depth 2" or 3" at a time.
Yes, I have read the fenderguru article. I figured to start with the original layout and modify if needed.
Pine is actually supposed to sound really nice, and very lightweight. Maybe just add some strategic bracing for strength. Not really an issue with the 10lb Reapers anyway. The 3-piece back is a good idea to keep it simple and versatile. Reaper 55's can be used in an open cab. I just don't know how well they can handle the low bass notes in an open or undamped cab. Consider Classictone iron if you don't have something else in mind. Great stuff for the money.
AFAIK, the Bassman tone stack isn't that scooped anyway, so it might be fine as is. Simple mod if you need it though. I like the idea of changing the standby switch to a GNFB option. The standby switch really isn't needed and is potentially dangerous as implemented. I'd use a 3-way GNFB option if you try that. Robrobinette.com has lots of mods like that. I'll leave off on that. Love to hear a demo when you get it done.