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Old 05-08-2013, 03:44 AM   #1
controlfreak
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50W head into 50W speakers? Does that work?

Hey folks,

I'm running a 100 watt head, with 2 power tubes pulled, so effectively a 50W head and i just picked up a new 2x12 cab with 2 25W speakers in it giving an 8ohm load. Will these work together or would i be driving these speakers too hard?
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Old 05-08-2013, 03:45 AM   #2
greeny23
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wait, did you just pull the tubes or is it meant to be like that..?
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Old 05-08-2013, 04:17 AM   #3
controlfreak
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I pulled the tubes. It's 4ohm head with 4 power tubes running or 50W and 8ohm with 2 power tubes pulled. It's been biased to be 50W so all's good with the amp.
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Old 05-08-2013, 06:41 AM   #4
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Wait, what? If you pull two tubes you turn down the impedance switch. ie if you have an 8 ohm cab you run the head at 4 ohms if you pull the tubes. Am I missing something?
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Old 05-08-2013, 07:25 AM   #5
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Quote:
Originally Posted by controlfreak
I pulled the tubes. It's 4ohm head with 4 power tubes running or 50W and 8ohm with 2 power tubes pulled. It's been biased to be 50W so all's good with the amp.

No you are wrong.
Pull 2 tubes and the ohms actually drops, so f you pull 2 and it normally runs a 4ohms the amp would have to be switched to 2ohms to run a 4 ohm cab. You are gonna blow something.

What amp are you using
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Old 05-08-2013, 07:55 AM   #6
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Exactly what I was thinking. I'm running my Marshall that way at the moment and I'm thinking, "huh?"
I've got my cabs wired up as 10 ohms so with two tubes pulled I run it at 4. Close enough. But what the TS is saying sounds scary. Unless it's some weird amp with switches we don't know about.
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Old 05-08-2013, 07:58 AM   #7
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Ye're missunderstanding me.
The amp setup is fine. It's an 50W head running into two 25W speakers.
The amp is set to run an 8ohm cab and this cab is indeed rated at 8ohms.
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Old 05-08-2013, 08:03 AM   #8
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It's a 50W amp with an output transformer for a 100W amp. They're different. I think we are understanding you perfectly from what you just said. The amp should be switched to 4.

The speakers will be fine unless you are diming the volume. In which case they probably won't blow straight away but you'll wear them out faster. You'll also get speaker breakup which you may or may not like depending on what you are playing and/or taste. There is a chance of blowing them if playing dimed, you're pushing the envelope let's say.
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Last edited by Cathbard : 05-08-2013 at 08:05 AM.
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Old 05-08-2013, 08:55 AM   #9
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Quote:
Originally Posted by controlfreak
Ye're missunderstanding me.


then help us out and speak plainly. how about just telling us the model of amp you have so we can find out what the original specs were. that way we aren't doing math from incomplete information.

...and a 50 watt rated cab will be fine for a 50 watt rated head.
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Old 05-08-2013, 09:29 AM   #10
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^ It's a 70's silverface Bassman100 head. I am running it at the moment into a 8ohm 2x12 cab with Jensen's and this config has worked for me for a long while now. The amp is normally 100W into 4ohm cab but with 2 power tubes pulled it's setup for an 8ohm cab.
What I'm asking here is will an 8ohm cab with two 25W speakers be basically the same thing as I'm already doing?
Hope this is clearer?
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Old 05-08-2013, 09:42 AM   #11
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I run this way as well and on my amp (Splawn) with the impedance dropped in half (not doubled). I have a 100 watt amp that would normally run 4 tubes and a speaker out of 8 ohms. I pulled two tubes, following Scott Splawn's advice, and now I run at 50 watts with 2 tubes and a speaker out of 4 ohms (cab is 8 ohms and 60 watts I think). My amp is similar to Cathbards. Marshalls are based off of Bassman's so I am assuming you would need to do the same thing as us but I'm not an amp tech. I've never heard of anyone doubling their impedance when they pull tubes.

Wattage wise, I would think you would be fine but some people would say you need a bit more in the cab than the head but with RMS being such a variable it is anyone's guess.
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Old 05-08-2013, 01:11 PM   #12
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It's a 4 ohm output put so that's correct with an 8 ohm cab if two tubes are pulled.

I've told you about the power rating. You're pushing the limit but unless you runn the amp on 10 you should be ok. Even then you'll probably get away with it for quite a while but you'll get some speaker breakup.
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Old 05-09-2013, 08:04 AM   #13
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Quote:
Originally Posted by controlfreak
^ It's a 70's silverface Bassman100 head. I am running it at the moment into a 8ohm 2x12 cab with Jensen's and this config has worked for me for a long while now. The amp is normally 100W into 4ohm cab but with 2 power tubes pulled it's setup for an 8ohm cab.
What I'm asking here is will an 8ohm cab with two 25W speakers be basically the same thing as I'm already doing?
Hope this is clearer?


there seem to be a lot talking around specs and things were getting confusing.

yes that does help.

i wouldn't think twice really about running a 50 watt cab with a 50 watt amp, of course i like to drive the hell outta my speakers too. but as mentioned earlier: if you wanna keep the speakers clean or if you just want extra power handling then maybe you should look at another cab.

i seriously doubt many of us play with our amps cranked all the way up though, and with most speakers being pretty conservatively rated i don't think a 50 watt cab would be an issue with a 50 watt head.
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