sonic I-40

[walter]

i picked up this amp locally the serial #s are44991,was wondering how old this baby is,its got 6550s can i use different tubes to get more distortion or should i just keep usin mah bigmuff an rat fer that?it has two speaker outputs as well,can i run a 2x12 4 ohm cab out of the 4ohm output while i run a 4x10s out of the 8ohm or would that mess the amp up?im fairly new to this whole idea of understanding what im playing through so if you can dumb it up fo mah dumbass,also i have a sunn 4x10 cab is there a way to find out what the impedance is w/out using a load tester er whatnot?ie does anyone know what ohm sunn 10" transducer guitar speakers are rated at?thanks sorry fer the novel im just excited and dont wanna blow anything up

[Isaac]

Sunn 4x10 cabinets are 8 ohms.

The output transformer has three taps, at 4, 8, and 16 ohms. The old amps are wired either 4/8 or 8/16. The way it works is that the higher impedance is wired to the main speaker out, the lower to the other jack, usually labeled "External Speaker" or something like that. The trick is that, once a plug is inserted into the External Speaker jack, the main jack is disconnected from the higher impedance tap and connected to the lower. In your case, that means that both jacks will then be connected to the 4 ohm tap. They are not separate, so you cannot run an 8 ohm load on the 8 ohm jack and a 4 ohm load on the 4 ohm jack.

So  8 ohms on the 8 ohm jack, 4 ohms on the 4 ohm jack, or 8 ohms each on both jacks, for a 4 ohm total load.

[walter]

thanks man-that helps out alot-do you know of a way to wire two 8ohm speakers so that the impedance is a total of 8 ohms-i believe the way they are wired now its at 4ohms-thanks so much fer yer help

[Isaac]

This gets asked a lot. The quick answer is no, it cannot be done.

Here's the longer answer. There are only two basic ways to wire drivers together, in series and in parallel. Two 8-ohm drivers in series gives you 16 ohms, in parallel 4 ohms. That's it. Unless you want to add in high power resistors, which would suck up a lot of the power you probably want to go to the drivers, and maybe change your sound.

[walter]

cool,i also have beta402 cab that is wired at 4 ohms-it has two other input jacks labled series and parrallel-if i plug another 4 ohm cab into the parallel jack that should mean that the total impedance of the cabs im runnin is 8 ohms-right?

[JoeArthur]

Two four ohm cabinets in parallel would be two ohms.  You would have to run them in series to get eight ohms.

[walter]

ahh yes sorry this whole ohm thang is fairly new to me,i certainly do pershaite it

[Isaac]

How many drivers does the Beta 402 cabinet have? I ask because it would be better, I think, to wire the two 4 ohm cabinets to 16 ohms, then run them in parallel for an 8 ohm load.

[walter]

its a 4 12 cab,i guess that means it has 4 drivers,it has three output jacks one is labled 4 ohm speaker,the other two say series and parralell-ihope this makes sense-thanks guys

[Isaac]

I'm not familiar with the Beta gear, but, at a guess, I'd say the 4 ohm speaker jack is the input, and the other two are for daisy chaining. One would connect the next cabinet in series, the other in parallel.

If the Beta 402 is a 4 ohm cabinet, as appears to be the case, you can wire it for 16 ohms, wire the 212 for 16, and run them in parallel. Or, if my guess about the jacks is correct, just run the 4 ohm 212 from the Series jack. Make sure it works that way before you do, though.

[walter]

yeah the 212 thru the series works to make 8 ohms-now can i run a 8 ohm thru the parallel to make it 4 ohms?

[Isaac]

I would think so, but remember that now you're powering three cabinets through one speaker cord. Why not use two from the amp? One from each jack.

[walter]

ah yes-thanks for yer help isaac-im a little bit slow sometimes