I've got the chance to buy a seventies Fender Bassman 70, cheapish. I understood it's a 70 watt amp.
As I'm currently using an Orange SP410 or an Orange SP210 cab (depending on the occasion, and in combination with a bass terror that I want to get rid of), does anyone know how the Bassman will combine with either of these modern 600w/800w cabinets?
Also, the cabs are 8 ohm, while the Bassman is 4 ohm.
I'm wondering both how it will sound (but I'll test that at the dealer's house) and if something could go wrong.
Those fenders were made for 4ohms but can handle 8 fine. If the 70 is essentially a 2-power tube 135, the ext. speaker out will be a switching jack that puts the outputs in series and accesses an 8 ohm tap in the OT. That means you can put a shorted dummy plug in the main speaker out, plug your cab in the ext. speaker out and get the 8 ohm tap.
No issues with the watt ratings...no such thing as underpowering, only overpowering.
Or would I be better of buying an Aguilar S210 cab to go with it... As it is 4ohm and 250 watts?
Thanks Will, hadn't seen your reply jet while I was typing. But do you think I'd get a better sound if I matched it with a 4 ohm cab?
And is there a thread somewhere on how to make and use a shorted dummy plug?
No need to buy new cabs, unless you just want to. You don't have to for this amp.
For one 8 ohm cab, put a dummy plug in the main out and plug the cab in the ext. out. Although the amp will handle it if you just plug it in the 4 ohm main out anyway.
For two 8 ohm cabs, connect them together using the jacks on the back of the cabs and plug one speaker cable in the 4 ohm main out on the amp.
With 4 ohm cabs you just plug the first one in the main out, and the second one (if you're using 2) in the ext. out.
The thing will have nice, classic fender tube tone, just won't go very loud, so be aware of that. Probably use your full stack for everything outside of a coffeeshop or jazz joint. Might get away with using the 410 with an okd school blues trio, not guitar slinger stuff. Be prepared to mic it up for any bigger, louder gigs.
It'll double as a guitar amp too if you want one. Has the sparkly fender cleans and takes to pedals well. If you go that route, pick up an Electroharmonix Holy Grail reverb pedal. Pretty convincing spring sound on that one and not overly expensive.
I used many Bassman amps in my day. Key will be to get the most efficient cabs you can find for the fairly limited power/watts the Bassman 70 will provide. The amp is a very linear design, so it will stay clean close to its upper power limits.
Some tube amps will have a switch on the back you just set to whatever speaker impedance you're using, like 2, 4, 8, etc. Those fenders use a "switching jack" on the extension speaker outs that switches between the various transformer taps internally when you put a plug in the jack, so you kinda have to know what to pkug in where depending on how many and what impedance speakers you're using.
The dummy plug "tricks" the amp into switching to the 8ohm tap, even though you're plugging your speaker into a jack labelled "4 ohms".
Fender PA-100 for BASS
Thanks a lot!
I also find a Fender PA-100, whis has two outputs both labelled 8 ohm. Does anybody have experience with these as bass amplifiers? I'm looking for that warm Fender tone, distortion not so much.
Is it possible to just plug ONE cab in, using only one of the outputs? (I'm asking because this is originally intended as a PA amp)
As it is cheaper than the Bassman 70, and 100 Watts, I might check them both tomorrow.
I'll use my Orange SP speaker, if some of the more technical guys give me the green light!
Totally different amps.
Bassman Ten 70 is of an UL (Ultra Linear) design, and while some folks like it, Hi-Fi mainly, it's IMO pretty far from the "regular" behaviour of a tube amp. IME/IMO nothing like a regular Bassman.
PA 100 is a wonderful, very under-appreciated "normal" (non-UL) amp.
IMO everyone should snag one while the prices still are what they are.
A nice mod-platform, essentially 4 pre's to mess with, and most importantly, by modding one, nothing even remotely valuable is lost. Decent tone with bass as-is.
Only one OT secondary, so either 2 8Ohm cabs (parallel) or one 4 Ohm.
I've run mine with both loads and it's been OK.
I prefer the designed load of 4Ohm though.
On a plus side, it's actually a very good PA amp for vocals, ACG's and such.
Perfect for that small club gig.
Out of those two, my choice would definitely be the PA100.
The Bassman 70 is a nice enough head for "that classic Fender sound," but, it sure won't go very loud.
I kept an old Bassman 50 around for studio use for a long time, but for live anything, it was just never gonna cut it. For me...
I agree the PA100 being the nicer amp of the 2.
Also more flexible, versatile and easier to use. Doesn't have the crazy switching jack/transformer tap scheme of the 135 and 70.
Thanks guys, I'll check the PA100 tonight.
Now about the ohm, which I'll probably never truly understand;
is it ok to just attach ONE 8 ohm speaker or do I HAVE to attach two 8 ohm speakers (which means that I ALWAYS have to bring 2).
Because I have no 4 ohm speakers I hope I can work with the 8 ohms I have.
And if I can, what would be the disadvantage of that, less power?
Ok, maybe this is a stupid question, that's why I'll just ask it:
If it's needed to plug something in both speaker outputs, could I just plug two cables in the SP210 (rated 8 ohm and having 2 inputs and parrallel sockets)
I won't recommend that, but I have never heard a Fender to smoke because of 4-8 mismatch.
A bit longer answer is that to fully understand how and why it's usually important to have the exact designed nominal load on a transformer coupled output section (99.9% tube these days) would require quite a bit of reading about tube amplifier design.
A tube has a certain load curve, and its behaviour and characteristics depend on the load, ie. at which point of that curve it operates. That load is the speaker, but since speakers are very low impedance 1-32Ohm typically, and tubes are high impedance devices of 10000's of Ohms, the transformer is needed to provide the "gearing".
Now, if the final load = the speaker is changed, also the load the tube(s) see is changed (radically), so the operating point on the load curve shifts.
If the amplifier is designed to accept that shift, or if the transformers impedance ratio is chosen to allow the tube(s) to work with both loads, all is golden.
The power is reduced just a hair, the bias will be slightly out of whack, the tubes and the OT will have to work a bit harder.
There has been several different variations of those amps though, and given their age, who knows what OT there is.
And if the OT has been swapped, what is the tap the tech used.
Or if the jacks are still wired the original way.
Apologies for probably confusing You even more, but that's how these amps tend to be.
The dummy plug that was mentioned earlier, works with certain amps that have several OT secondaries, but the manufacturer cheaped out on the impedance selector switch.
Like Bassman 135 & PA135 ;).
A recepie for disaster if You ask me, give me a Marshall impedance selector any day over that nonsense.
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