'56 Bassman speaker load question

[vistacruiser]

My harp player gave me a "homade" bass amp that was taking up space in his apt. for the last 30 years or so.

Turns out to be a model "5E6" Fender Bassman, with 2 inputs and dual rectifiers, in a "head" style box, and a 15" spkr in a homade cab.

The amp seams to work like it should. I have tried it with the 8 ohm 15" it came with, (thumb size hole in cone now patched); with an SWR Son of Bertha 1-15, 8 ohm; and a 4 ohm Ampeg 610hlf. It sounds really nice and plenty power full with the Ampeg cab, just o.k. with the SWR, not as loud, breaks up too easily.

Before I do some damage to this rare gift, I would like to find out what impedance these can safely run at. And what load the 4-10's in the original combo had?

I've played Ampeg tube heads for decades, never had a Fender. Thanks for any help on this.

[T-Bird]

Hi.

AFAIK and IIRC, the Fender tube amps are designed for 4 Ohm operation.

I haven't measured it, but according to some sources, the OT specs were chosen in a way that allows similar enough load for the tubes in both 4 & 8 ohm load situation, ie. the "correct" impedance is somewhere between those two.

Regards
Sam

[vistacruiser]

Hey Sam,

I like the sound of that, if I can run this at 4 ohms and 8, it will be useful.

Think the orig. spks were 16 ohm, in parallel, for 4 ohm total?

[walterw]

old fender amps were designed for however many speakers they had, all 8Ω and all in parallel.

that bassman (if that's what it really is, as opposed to a modern copy, and thus who knows what) was a 4x10 combo; thus, it was designed for 2Ω.

[walterw]

fenders are famous for taking abuse, so you can mis-match the load a bit; it'll just get less efficient, like you noticed with that 8Ω 15. (it's pushing things to go two "steps" away, so 4Ω is OK, 8 is pushing it, 16 is a bad idea.)

[billfitzmaurice]

The 56 Bassman was a 2 ohm 4x10. It will probably handle 4 ohms OK, 8 would be pushing it, 16 ohms would be out of the question.

[vistacruiser]

Thanks Walter and Bill for that info. That's good news, I'll keep the load at 4 or less for serious work. I have a pair of 4 ohm Cerwin Vega 18's I could try, now that will get me to 2 ohms!

This is for sure an old bassman, ground switch, cloth insulation, point to point no PCB, 7 tubes (RCA & Westinghouse). I used on-line schematics and serial# info to determine the age.
BM00550-BM01200 = 1956

[walterw]

you do realize you could just sell it to a guitar player for enough to get a nice actual bass amp, right?

using one of those low-powered vintage tweed beauties to play bass through is like hauling a plow with a racehorse.

[BogeyBass]

not a expert here but, i think if it was a actual fender transformer it would be manufactured by Triad.

The 4x10 amps had a single 2ohm tap on 5D6 and 5E6

looking around on some aftermarket transformer sites, shows 3 different Fender/ Triad Transformer part numbers #45249, #2820 and #2485.

take a look at your output transformer, should be the smaller one, and see if you can find manufactures name or part number.

If its a home built amp it may actually have a reproduction/upgrade transformer with more taps available.

[majortoby]

Originally Posted by walterw

you could just sell it to a guitar player for enough to get a nice actual bass amp.

I must disagree. Low wattage aside, I find the tone from an old bassman amp to be positively gorgeous on bass. If nothing else, it's a SWEET recording tool, IMO....Grats on the score!

[T-Bird]

Hi.

The old farts to the rescue , I actually thought the original speakers were 16 Ohm ones, like in the latter 412 cab I once had.



Missed this the first time around, HOMADE?

I suppose it supposed to be home-made, not made by a ho? .

If that's true, then a bit of reverse engineering is in order if the taps don't show the impedances, or if there isn't a reliable identification code in the OT.

Originally Posted by walterw

you do realize you could just sell it to a guitar player for enough to get a nice actual bass amp, right?

using one of those low-powered vintage tweed beauties to play bass through is like hauling a plow with a racehorse.

Yep, I can vision this...

"What on earth is that, a BEHRINGER , where's the amp I gave You?"

"The good folks at GC traded that old low wattage head straight to this 600W combo, I think I got a deal"


What a grand way to lose a friend and a bandmember (or ones place in that band).





There's always the chance of miking it if the power isn't enough.

One additional thing. Since it came from a harp player, check the phase inverter tube. Most I know use asymmetrical PI in order to create THAT harp tone. Doesn't usually sound too good with other instruments

Regards
Sam

[will33]

Most of the old bassmans wanted a 4ohm load. Anything less than that is fine, 2, 1, etc. They could handle up to a double upward mismatch, meaning running an 8ohm speaker on a 4ohm bassman but don't go past that. Running a 4ohm or less is the best policy.


Congratulations,......enjoy.

[vistacruiser]

The OT is a #2820, PT is #7993.
My observations tell me this is a complete 5E6 chassis, separated from its orig. 4-10 cabinet some time in the foggy 70's, and shoehorned into a home-made "head" cab. The knobs faced front, tranny's on top and tubes faced the rear. The odd arrangement is what tipped me off to research it's origin, Fender combo.
Not sure what this one would bring, certainly not top $$. I may just keep it as a "head", and make a nicer tweed box for it, and have some fun with it.

Sam, the harp player never messed with it, still has the 12ax7 PI, in fact it has 12ax7's where there should be 12ay7's in the first two sockets. I guess that's how he got it, nearly 30 years ago.
Now if I wanted to help him get that harp tone in his current Crate V50 amp, what tube would I want to use in the PI, 12dw7? I got a few of those around.

Thanks for all the help everyone!!

[will33]

Ok, this old fender is dead weight, you need to get rid of it. PM me and I'll arrange prepaid shipping. All you have to do is drop it off and I'll take this old headache off your hands. No charge to you of course...consider it a "don't have to pay it back" favor. I'll handle everything,

Thanks,

-Will

[T-Bird]

Hi.

Originally Posted by vistacruiser

The OT is a #2820, PT is #7993.
My observations tell me this is a complete 5E6 chassis, separated from its orig. 4-10 cabinet some time in the foggy 70's, and shoehorned into a home-made "head" cab. The knobs faced front, tranny's on top and tubes faced the rear. The odd arrangement is what tipped me off to research it's origin, Fender combo.
Not sure what this one would bring, certainly not top $$. I may just keep it as a "head", and make a nicer tweed box for it, and have some fun with it.

That's one hell of a score if You ask me.
Missing the box means value reduction of course, but aftermarket boxes are pretty cheap considering (there's even some that You can actually play bass through ), and the guts are after all what counts, not the cosmetics.

Unfortunately I'm not versed enough with Fender (Triad) OT's to tell what the correct load impedance for Yours is, but Google should help if the more knowledgeable people won't chime in first.

Originally Posted by vistacruiser

Sam, the harp player never messed with it, still has the 12ax7 PI, in fact it has 12ax7's where there should be 12ay7's in the first two sockets. I guess that's how he got it, nearly 30 years ago.
Now if I wanted to help him get that harp tone in his current Crate V50 amp, what tube would I want to use in the PI, 12dw7? I got a few of those around.

Yep, that's the one. IIRC a drop-in to any common 12AX7 PI amp. There's also PI mods for variable asymmetry using common 12A*7 family tubes. I'm a bit busy ATM, so I won't be able to check the Crate schematics, but I see no reason why wouldn't it work.

IMHO/IME, 50W is way too much for a good harp sound in a club though, but the PI mod should help for getting that dirty sound without shattering everyones eardrums.

Regards
Sam

[projectMalamute]

Originally Posted by vistacruiser

Now if I wanted to help him get that harp tone in his current Crate V50 amp, what tube would I want to use in the PI, 12dw7? I got a few of those around.

Wait, dude owns a 56 Bassman and is playing out of a Crate?

I suggest the following: offer to take that old beat up amp off his hands for like 50 bucks and find some for real musicians to play with.

[JHAz]

Do you see the 5E6 or 5E6A tube chart inside the amp? The very first bassman amps were 1 15 configuration, but I think that's 5B6. IDK the correct impedance match for them, but 8 ohms seems likely. It still could be a copy, too, whether a home made one (go to tedweber.com to see a full range of fender, marshall and vox clone kits) or one of the many commercial clone builders . . . vintage-"correct" materials are a big deal in that market . . .

The 15 blew, a lot, so fender went to the 4 10s in parallel structure. Every one of these is a 2 ohm amp, AFAIK. With 4 speakers, you could blow one and keep on keepin on.

Appropos of discussion elsewhere of the engineering chops that Leo et al brought to speaker and cab design, even in the early 50s folks new that an open back cabinet would result in significant bass cancellation, but Leo et al built open back bassman amps until the 60s. As brilliant as many of the early fender designs are, and I love them, they also were, uh, value engineered. recall that Leo origianlly avoided truss rods in his guitar necks to save money, figuring he could replace a few necks cheaper than putting a truss rod in every one. The market soon corrected that error.

[pgk]

all tweed 4 x 10 bassmen are a TWO ohm load, no exceptions.

so, take two 2-15 cabs, each wired for a four ohm load, connect them together for a 2 ohm Total load and let 'er rip. that tone would very likely scare the living daylights out of you. my old tech once measured the frequency response of a tweed bassman and marvelled at it; if i remember correctly it's low end response was essentially flat down to 30hz....

[billfitzmaurice]

Originally Posted by JHAz

Appropos of discussion elsewhere of the engineering chops that Leo et al brought to speaker and cab design, even in the early 50s folks new that an open back cabinet would result in significant bass cancellation, but Leo et al built open back bassman amps until the 60s.

Fender's design philosophy for a bass amp was to take a guitar amp and make it bigger, which is pretty much the same as how the PBass came about, basically being an over-sized electric guitar. The 59 Bassman is so prized as a guitar amp because that's what it is in all but name. Yes, the acoustical engineering community knew about the deficiencies of open back cabs even in the 1930s. Leo wasn't a member of that community. Where guitar amps were concerned that wasn't much of a hindrance, but where bass was concerned it very much was.

[AMJBASS]

If the amp has been sitting around for a while, it might not be a bad idea to have the filter caps replaced. Nice score though. I was pretty close to buying one of those old single 15 bassman combos a while back and wish I did!