6L6s and cabinet selections HELP!!!!

[xbox540]

hi guys i have a tube amp head and i wanna run a full stack on it so on the back of the amp are 4 ohm 8 ohm and 16 ohm......which ones should i plug into so that i dont blow out my cabinets or even worse my amp? AND ALSO if im using Groove Tubes 6L6S tubes can i use 6L6GCs or any other 6L6s of that sort??

[gerryc]

Can you give a bit more info? What kind of amp is it? Do you know what the output power is (watts?). Is it just a pair of 6L6's or a quad, for instance. The most amount of power you'd get from a pair would be about 50 - 60 watts, 100 - 120 watts for a quad. What do you mean by a stack? One or more cabinets, 4x10s, 2x15s, etc?

[EC8010]

Could you also please use capital letters and punctuation where appropriate? Bear in mind that someone who writes English as their second language may be the person you need to help you, and they're taught grammatical English, not textspeak.

[Dave Cigna]

As far as the speaker connections go, this is one of those situations where it would be better for you to learn how to determine the answer yourself than to have someone give it to you anyway.

Full stack traditionally means two cabinets each with 4x12 speakers. But, 4x12 cabs come in different impedances. They might be 2, 4, 8, 16, or 32 ohms. Then, since you have two of them, you have to decide if you want to connect them in series or parallel.

Speaker impedances add like resistors. In series they simply add R = R1 + R2. So if you connect two 8 ohm speakers in series then they look like 16 ohms and should be connected to the 16 ohm jack on your amp.

It's a little more complicated in parallel: 1/R = 1/R1 + 1/R2. If both speakers are the same (R1=R2) then it's a lot simpler: the combination is just half that of either speaker. So two 8 ohm cabs in parallel should be connected to the 4 ohm jack.

Don't know what impedance your cabs are? Open them up and figure it out using the info above. All four speakers might be connected in series, all in parallel, or (likely) in series/parallel. Series/parallel means that in each box two will be in series, the other two will also be in series, and then those two pairs will be connected in parallel. Figure out the total impedance in steps.

For example, suppose you have four 8 ohm speakers in series/parallel. What will each series pair look like individually? (The answer is above.) Then consider those two pairs. What will they look like when put in parallel? (Again, I've given you enough info above to figure it out.)

-- Dave

[xbox540]

as far as the specs on the amp go, its a peavey ultra 60 amp, the series 1, and it runs on two 6L6S tubes. and both of my speaker cabinets are 4x12s and run at 8 ohms each so if that makes it easier to figure out please help me....

[gerryc]

Originally posted by xbox540
as far as the specs on the amp go, its a peavey ultra 60 amp, the series 1, and it runs on two 6L6S tubes. and both of my speaker cabinets are 4x12s and run at 8 ohms each so if that makes it easier to figure out please help me....

Ok. User's manual http://www.peavey.com/search.cfm?c=5&term=ultra+60
says to use 6L6GC's. The 6L6S are probably OK, except that they are supposed to distort sooner and give you a little less power if that's what you want:

http://www.torresengineering.com/softsoft.html

The owner's manual also says that if you use the 4 and 8 ohm jacks on the amp, the output impedance of the amp is 4 ohms. So you would plug one of your 8-ohm cabinets into the 4 ohm output, and one into the 8 ohm output.

[DigitalJunkie]

These might be useful for figuring out series/parallel impedances.

http://www.the12volt.com/caraudio/boxcalcs.asp
http://www.the12volt.com/caraudio/wo...igurations.asp

There used to be a nice diagram on that site,but I can't seem to find it now.

[xbox540]

ah i see now, that makes sense too. but say i want to switch from the 6L6S that i have now to some 6L6GC. would i need to rebias the amp or could i just switch them out no problem?

[gerryc]

Originally posted by xbox540
ah i see now, that makes sense too. but say i want to switch from the 6L6S that i have now to some 6L6GC. would i need to rebias the amp or could i just switch them out no problem?

Unless the amp has adjustable bias (some do, some don't and are designed with a fixed bias setting that works properly with the type of tubes that the amp was designed for), then I would expect that plugging in a set of the original types (6L6GC) would be fine. If someone (a tech for example) modified the amp's bias circuit to work specifically with 6L6S's than it should probably be changed back to it's original setting. Highly unlikely though.

[xbox540]

ok cool cuz im not really a techie or anything so rebiasing and doing things like that would be WAAYYY out of my league and taking it to a tech is pretty expensive around the area i live in, but hey if i dont have to rebias then GREAT! lol thanks guys for your help