Has anyone ever ran a Bandmaster/ Bassman type amp (2 6L6-4ohm) with an 8ohm speaker? I have always thought mismatching was a no-no, but I recently heard it works OK with these types of amps. Changes the sound a little, drops the power down. Steve Kimock seems to prefer this type of mismatch, his sound is killin'. I am interested in the lowered output and saving some space by using a single 8ohm 12.
2 6L6 amp/4ohm OT + 8ohm speaker load?
- Thread starter taterhead
- Start date
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muchxs
Doctor of Teleocity
"Everyone" does it. "No one" worried about it until recently when the Slightly Educated Impedance Police hit the web.
The guideline is that you can run half or double the correct load and it will work fine. Like any rule there are exceptions. Vintage Marshalls and most Matchless amps are underloaded to begin with, that means if you use an 8 ohm speaker on the 4 ohm tap you're actually correct... by the book. Tube amps "like" more load better than less load... up to a point.
strat a various
Friend of Leo's
I've been doing that with my SF bassman for over twenty years, but I still feel uneasy about it. Flyback voltage is scary to me, since I'm not a tech. One of these days I'll get around to setting up a 4 ohm cab for it. So far, so good.
tonfarbe
Tele-Afflicted
As far as I know, feeding a higher Ohms speaker is safe (8 Ohms speaker on a 4 Ohms OT) but not the other way around (4 Ohms speaker on a 8 Ohms OT).
strat a various
Friend of Leo's
This whole subject gets beaten to death every week or so. There are lots of threads that can be searched that pretty much amount to: most good tube amps, with a couple of exceptions, can run at 100% mismatch with no problem, but, it's BETTER to match up impedance to avoid OT damage and frying other components.
Wally must have weighed in on this topic many times, and I don't know anybody around here that knows any more about tube amps than him. He's the guy to ask, or one of the other real techs hereabouts.
The guy that works on my old Fenders warns against any mismatch, especially at high volumes through vintage amps. I just got used to the cab I use, I'll have to replace it soon. Works for now.
Wally must have weighed in on this topic many times, and I don't know anybody around here that knows any more about tube amps than him. He's the guy to ask, or one of the other real techs hereabouts.
The guy that works on my old Fenders warns against any mismatch, especially at high volumes through vintage amps. I just got used to the cab I use, I'll have to replace it soon. Works for now.
Wayne Alexander
Friend of Leo's
With Blackface and Silverface type Fenders in good shape, and amps closely copied from them (Allen amps for instance) you can do the 100% mismatch without hurting the amp. Do NOT do this with a Vox or Marshall or amps copied from them - they're not designed for it and you can blow output tubes, various resistors, and the output transformer itself.
otterhound
Poster Extraordinaire
I am using a '66 Bassman with a 2 Ohm cabinet/speaker , Fender Jazzmaster 112 . I contacted Fender with the same question . Their reply was that it is OK to use my Bassman , which is a 4 Ohm amp with a same or lower rated speaker . Their recommendation was to not use a higher rated speaker 8 or 16 Ohm speaker with it because of possible damage to the amp . In the long run , it is yours to do with as you like .
backline
Tele-Afflicted
Can I, Does it matter, Will it hurt anything? Like mentioned already, it has been asked a million times before. If it says 4 ohms, that is what you need, just show it 4 ohms. Anything else is just a guess. There are amps that have been run mismatched for years with no apparent problems, so who knows. It just seems so much easier to do the right thing.
On paper, excessive current will burn up your out tranny if the impedance load is too low. But tubes are "current limiting" devices so they will protect your amp from too small a load right? But what about no load, isn't that too small a load?
So that means it would be safer to run your amp at a higher impedance right? But as "strat a various" already brought to your attention, there is the very real danger of fly back voltage at a too great load. Sssoooooo..... when is a load too small or too big? Who wants to guarantee that answer?
If you are going to play guitar, you need to have more than 1 speaker, 1 cabinet, 1 cable, etc. etc. Over time, a player needs to build up an arsenal of speaker cabs of different impedance. Or at least the ability to swap speakers in and out of the same cab to accommodate different amps and guitars. Your enjoyment of playing will greatly increase if you do not gamble all on the same horse.
Good Luck
On paper, excessive current will burn up your out tranny if the impedance load is too low. But tubes are "current limiting" devices so they will protect your amp from too small a load right? But what about no load, isn't that too small a load?
So that means it would be safer to run your amp at a higher impedance right? But as "strat a various" already brought to your attention, there is the very real danger of fly back voltage at a too great load. Sssoooooo..... when is a load too small or too big? Who wants to guarantee that answer?
If you are going to play guitar, you need to have more than 1 speaker, 1 cabinet, 1 cable, etc. etc. Over time, a player needs to build up an arsenal of speaker cabs of different impedance. Or at least the ability to swap speakers in and out of the same cab to accommodate different amps and guitars. Your enjoyment of playing will greatly increase if you do not gamble all on the same horse.
Good Luck
ThermionicScott
Poster Extraordinaire
I believe the rule of thumb is/was that you don't want the plate voltage to swing to more than twice the rated plate voltage. Some datasheets for the EL84 list the regular 300V plate rating, but also a 550V zero-current plate voltage.
My hunch is that this is how Fender got away with using higher voltages than the datasheets recommended -- the idle voltages are high, but the load impedance is lower, so the plate voltage can't swing up high enough to cause arcing or other problems.
Playing around with the load impedance changes the sound, too -- a higher impedance causes more odd-harmonic distortion and a lower impedance causes more even-harmonic distortion, but with less power output. Use whatever sounds best to you and doesn't cause fires.
- Scott
backline
Tele-Afflicted
I'm gonna put that on my tombstone.Use whatever sounds best to you and doesn't cause fires.
- Scott
