Silverface Fender Bassman safe @ 8 ohms?

[davelowell2]

I have a chance at one of these and would like to know if I can safely run it at 8 ohms. I have two 1x15 cabs, each 8 ohms. I get that both at 4 ohms is best, but what about one at 8?
Thanks.

[billfitzmaurice]

I've never heard of a Fender having problems with an 8 ohm load. But don't count on getting a lot of volume when running just one cab.

[pgk]

no problem, but you'll only be getting about 2/3rd's the total power the amp has, which ain't a lot to begin with

[T-Bird]

Hi.

Originally Posted by pgk

no problem, but you'll only be getting about 2/3rd's the total power the amp has, which ain't a lot to begin with

A link please?

The silverfaces (not bassmans though) I have benched have put about the same ~90 to 110W before clipping to both impedances with matched generic CP tubes. Only the below 80Hz or so region is marginally better with 4 ohm load, barely measurable, totally inaudible.

If 100 "tube watts" ain't a lot, one either has wrong speakers or is deaf to begin with. IME anyway.

Regards
Sam

[davelowell2]

Originally Posted by T-Bird

Hi.



A link please?

The silverfaces (not bassmans though) I have benched have put about the same ~90 to 110W before clipping to both impedances with matched generic CP tubes. Only the below 80Hz or so region is marginally better with 4 ohm load, barely measurable, totally inaudible.

If 100 "tube watts" ain't a lot, one either has wrong speakers or is deaf to begin with. IME anyway.

Regards
Sam

Well, that's good news for me, huh? So, I should be "safe" at 8 ohms, great!

[will33]

I've run my 135 a lot on 8ohm ported bass cabs and openback guitar cabs with nary a problem. Don't know if I'm stressing components or shortening it's lifespan or not but it hasn't caused any problems and is still the most reliable amp I've had.

Caveat: I'm no amp tech, just my personal experience.

I've sinced removed it from bass duties and it's my guitar rig now. I did have it biased to run on 2 power tubes for this but still don't know if or how that effects the taps for different impedance speakers.

I thought I read somewhere that the outs are in series so when you plugged into both outs it used an 8 ohm tap or if you plugged into the ext. jack instead of the main one it put you into the 8ohm tap. I don't know, could be some internet fantasy....I'll be opening it up soon to reglue and recover the headcase so I guess I'll have a look at the jacks then. Something about that series thing doesn't make sense though as mine works with 1 speaker plugged in the ext. jack and nothing in the main jack.

Whatever's going on, it ain't gonna explode if you run an 8ohm cab on it.

[Turock]

Originally Posted by pgk

no problem, but you'll only be getting about 2/3rd's the total power the amp has, which ain't a lot to begin with

You must be talking about SS amps, of which this is not.

[pgk]

Originally Posted by Turock

You must be talking about SS amps, of which this is not.

no, i'm talking about a stock sf/bf bassman, which btw is only 50 watts and not 100. it has a 4 ohm output transformer and it's maximum power is optimized for a 4 ohm load. 4ohm fenders are very tolerant of a 100% upwards impedence mismatch to 8ohms, but you will most definitely feel a loss of power and punch when you do that. noticeably looser sounding as well, and it'll fart out even faster, which may or may not be to your liking. put it on a 'scope with an 8ohm load; below 80hz may or may not be inaudible (???) but your ears will tell you different for sure, especially with a cabinet that is capable of 80hz and below. try it and see for yourself. when you feed a stock bassman/bandmaster/dual showman with it's proper 4ohm load it will always be noticeably louder and punchier than when using a mismatched 8ohm load. try it yourself and see, what else can i say? you won't hurt a thing either

[pgk]

I thought I read somewhere that the outs are in series so when you plugged into both outs it used an 8 ohm tap or if you plugged into the ext. jack instead of the main one it put you into the 8ohm tap. I don't know, could be some internet fantasy

no, i believe you're right. a 135's output jacks are wired differently from a trad fender's jacks. i have no experience with one but a friend owns one and says the same thing as you. if you plug into Just the ext speaker jack on a traditionally wired fender you'll barely get any sound at all. and i would think that's a dangerous thing to do for too long, as the amp in that scenario is essentially seeing no impedance load at all. that is not the case with a 135

[JTE]

Originally Posted by pgk

no, i'm talking about a stock sf/bf bassman, which btw is only 50 watts and not 100.

The Bassman 100 was 100 WRMS, though. Four 6L6's instead of the two in the 45-50 watt version which you're talking about.

John

[will33]

Originally Posted by pgk

I thought I read somewhere that the outs are in series so when you plugged into both outs it used an 8 ohm tap or if you plugged into the ext. jack instead of the main one it put you into the 8ohm tap. I don't know, could be some internet fantasy

no, i believe you're right. a 135's output jacks are wired differently from a trad fender's jacks. i have no experience with one but a friend owns one and says the same thing as you. if you plug into Just the ext speaker jack on a traditionally wired fender you'll barely get any sound at all. and i would think that's a dangerous thing to do for too long, as the amp in that scenario is essentially seeing no impedance load at all. that is not the case with a 135

Cool, thanks. I still can't figure how or if things are affected by running it at half power. Mine's essentially a bassman 67-1/2 now. Quite a rare piece, eh?

[pgk]

Originally Posted by JTE

The Bassman 100 was 100 WRMS, though. Four 6L6's instead of the two in the 45-50 watt version which you're talking about.

John

yes, but the op was asking about a stock silverface bassman. the same things i said apply to a 4ohm bassman 100 being run at 8ohms. it'll work just fine, but you're not getting the most out of the amp

[WhoDidTheElf]

Originally Posted by pgk

yes, but the op was asking about a stock silverface bassman. the same things i said apply to a 4ohm bassman 100 being run at 8ohms. it'll work just fine, but you're not getting the most out of the amp

If it's a tube amp and it has an 8ohm tap, shouldn't it run at 100 watts...?

[pgk]

again, to further clarify:

a bf/sf showman is 8ohms. a bf/sf dual showman is 4ohms, bf/sf bassmen 50/70/100/135 are 4ohms. they are all single tap amps, they do not have multiple taps.

[davelowell2]

The amp in question is a Bassman 100.

[Prodigal Son]

I have a Bassman 100. Although I now run 4 ohms exclusively (either 1 4-ohm or 2 8-ohm cabinets), when I first got it I ran it for the better part of a year with 1 8 ohm cabinet. Just had the tubes checked out and they were fine. Didn't even need the bias adjusted.

[johnk_10]

IMO, it definitely won't hurt a 4 ohm tube fender amp to run it at 8 ohms (i've done that from time to time) but to me, it does make them sound and feel a little bit more 'constricted' (or constipated ). IME, it'll sound like it has less headroom, clarity, dynamics, and punch.

[pgk]

thanks johnk10

to the op: even tho you did'nt say it was a bassman 100 all the same things apply. so rock on at 8ohms with no worries! when i was a kid we did that all the time because we did'nt know any better. and when we finally plugged say a bandmaster into a proper 4ohm cab it was like you got a little "gift"; it was bigger, louder, more solid and just plain better all around

[JTE]

Yep, the schematic I found for a Bassman 100 (http://www.drtube.com/schematics/fender/bassman100.gif) shows the "Ext. Speaker" jack is just run in parallel with the main jack. So, it's going to be a mis-match at the output transformer and the things that pgk's saying apply. 8Ω will work OK, but you won't have the power nor the overall sound you'd get with a 4Ω load.

John

John