Need help with Ohms/Head/Cabs

[RolloOfTheNorth]

I have only really ever used combo amps before and decided to upgrade to a head/cab setup. I recently purchased an Ampeg B25B head (500 watts max, 16 ohms) and I have 2 cabinets: a Hartke VX215 (500 watts@4 Ohms) and a Gallien-Krueger Backline 410BLX (400 watts@8 Ohms). I've tried to look up some info and got a little confused, so I decided to ask people who know what they're talking about. Is it alright and safe to play a set-up like this or can I damage something(s)? What can I do with my current equipment that will be ok? Thanks.

[James Judson]

You need to match watts to protect speakers. You need to match ohms to protect amplifiers. I generally run one amp and one speaker. So that is what I would recommend. If you choose to run and 8 ohm cabinet with a 4 ohm cabinet the total impedance the amp will see it 2.7 ohms. The mismatched impedance will result in one cabinet working harder than the other.

Will your amp handle a 2 ohm load? If no!!! Do not hook up both speakers.

[PeaveyPippin]

Everything I've looked up says that amp can handle an 8ohm load, so only hook up one of your cabs. But you should be on the hunt for the original matching B25B Cabinet it's going to give you the best compatibility for that rare head.

[NateS]

a quick google search yielded a thread on TB, where somebody with a manual said it was 130 watts at 4 or 16 ohms. It's also a tube amp, so you have to give it the correct impedance!

You can use the 4 ohm cabinet, but not the 8 ohm cabinet.

EDIT: More search is now saying either 8 or 16 ohm. Either way ,there should be a switch on the back of the head, with the two numbers beside it. Switch it to either 4 or 8, whichever it is, and use that same cabinet.

[MIJ-VI]

Ampeg b25b schematic
http://www.schematicheaven.com/ampegamps/b25b.pdf

[MIJ-VI]

From: How to run my ampeg b25b?

[NateS]

ok, so this post was true:

http://www.thegearpage.net/board/sho...d.php?t=228078

The amp was designed for 1 or 2 16 ohm cabs ,but if you put a bare 1/4" phone plug (unshorted or connected to anything) into the EXT jack , that would switch to the 8 ohm tap matching impedance to a single 8 ohm cab from the main output jack . The main output jack must be used first because it too has a switch which shorts to ground if not used giving no sound.

so, plug in your 8 ohm cab to the speaker, then plug a 1/4" plug to the ext. speaker, then turn on. You have to plug your cabinet in first, and don't turn it on until both plugsh ave a jack in them.

use something like this so it doesn't get shorted:

[Bass_Pounder]

Originally Posted by RolloOfTheNorth

I have only really ever used combo amps before and decided to upgrade to a head/cab setup. I recently purchased an Ampeg B25B head (500 watts max, 16 ohms) and I have 2 cabinets: a Hartke VX215 (500 watts@4 Ohms) and a Gallien-Krueger Backline 410BLX (400 watts@8 Ohms). I've tried to look up some info and got a little confused, so I decided to ask people who know what they're talking about. Is it alright and safe to play a set-up like this or can I damage something(s)? What can I do with my current equipment that will be ok? Thanks.

Originally Posted by MIJ-VI

From: How to run my ampeg b25b?

Looks like what you thought was a 500 watt amp is really only a 55 watt amp.

[MIJ-VI]

The b25b may draw 500 Watts of AC power from a wall socket but that's it.

[NateS]

yea, but it's 55 TUBE WATTS

if you like the volume and sound, use it.

[MIJ-VI]

Oh no...

[NateS]

that was meant to be sarcastic... ftr

[MIJ-VI]

[NateS]

Originally Posted by MIJ-VI

Oh no...

Originally Posted by MIJ-VI

...?

or am i incorrect that this i about the comment i made about tube watts?

[WarwickDude68]

If two 4 ohm cabs are hooked up to an amp that does not handle a 2 ohm load, how long before the amp will be damaged? Is it an instant thing or is it if you keep playing it that way for like a whole show? Just curious if anyone has experience with this misfortune?

[BassmanPaul]

Originally Posted by WarwickDude68

If two 4 ohm cabs are hooked up to an amp that does not handle a 2 ohm load, how long before the amp will be damaged? Is it an instant thing or is it if you keep playing it that way for like a whole show? Just curious if anyone has experience with this misfortune?

For a SS amp it depends. Some will die almost as soon as you play through them. Others will just overheat until they die. Others still won't event turn the speakers on.

Tube amps are more forgiving but you will compromise tube life. When and how a tube fails can damage your amplifier. It's always best to match speaker impedance with what the amp is expecting.

Paul

[WarwickDude68]

Thanks very much for the feedback, Paul.

[MIJ-VI]

Originally Posted by bassk81976

...?

or am i incorrect that this i about the comment i made about tube watts?

I have a dry sense of humour.