Calling All Tube Heads!!!

[goldtopchas]

Ok, I know this sort of topic has been adressed in the past, but I'm looking for specifics. I've got a 65' blackface super reverb chassis in a head cabinet. Whoever had it before did away with the 4x10 combo cab. I know it's supposed to drive a 2 ohm load. I use it with 8 ohms. It sounds great, and I kinda like that it's not as loud as it should be. I can crank it without it peeling anyones scalp off. I've used it at several gigs like this and countless times at home with no problems....YET. What would be the poss. failure here. P. tranny? output tranny? Both? This things been through the war. It's pretty beat. Will it eventually "melt down"? Thanks.

 

[gusfinley]

well...

There is a reason for matching impedences. Typically a mismatch of 2x or 1/2x is alirght. With the right speaker plugged in everything works just like it should. But plugging an 8ohm into a 2 ohm sould casue some trouble. When the impedence of the speaker is reflected through the output transformer the tubes will see an impedance 4 times greater than the optimal impedence. When impedences match up, you all the power from the tubes transfered through the output transfomer to the speaker. when you get a mismathc some of the power isn't being transfered but it being wasted somewhere, either in hotter tubes or a hotter output transformer also causing variations in frequecy response.

What kind of cab are you using? If you have more than one speaker you can wire them up for a lower overall impedence and get the cab closer to the required specs. Or look into a Weber Z-matcher ( www.tedweber.com) It will match the impedences between the Output transfomer and the speaker, and therefore reflect the correct impedence through the output transformer.....

 

[Henry Mars]

There is a reason for matching impedences. Typically a mismatch of 2x or 1/2x is alirght. With the right speaker plugged in everything works just like it should. But plugging an 8ohm into a 2 ohm sould casue some trouble. When the impedence of the speaker is reflected through the output transformer the tubes will see an impedance 4 times greater than the optimal impedence. When impedences match up, you all the power from the tubes transfered through the output transfomer to the speaker. when you get a mismathc some of the power isn't being transfered but it being wasted somewhere, either in hotter tubes or a hotter output transformer also causing variations in frequecy response.

What kind of cab are you using? If you have more than one speaker you can wire them up for a lower overall impedence and get the cab closer to the required specs. Or look into a Weber Z-matcher ( www.tedweber.com) It will match the impedences between the Output transfomer and the speaker, and therefore reflect the correct impedence through the output transformer.....

Nothing should get hotter .... the amp is not living up to its full power output potential. Normally a higher Z speaker will not hurt anything except power out put and possibly change the frequency response a little. Where you have to be careful is using say a 2 ohm speaker where an 8 ohm speaker is required. Then your out put XFMR could over heat and your tubes "melt" because you are trying to drive more current than the components can handle .... the out put power will also decrease and frequency responce goes down the drain.