Members bluecosmo5050 Posted September 19, 2016 Members Share Posted September 19, 2016 Hello, for my power amp I use a Mesa 50/50. It's extremely loud, even at 50 watts. I like to use two 2x12's with it, so I plug both of these 8ohm cabs into the 4ohm inputs.... It has two 4ohm and 1 8 ohm for each channel. The second channel has no load plugged into it, the manual says this is safe as long as the volume stays at zero on the second channel, and it does. If I did want to plug a cab into the second channel, two 8 ohm cabs, I'd just go 8 ohm in channel 1 and 8 ohm in channel two right? Because it's like having two 50 watt amps being stereo? It's been so long since I've used both channel I forgot how it worked. I know how it works with an amp head or with one channel. Then there is this question.... Instead of lugging around two tube power amps, if I'm only using one side, let's say a tube blows on side A, can I then just turn the volume down to zero, remove the tube that blew and switch the cabs to side B? Or do I need to remove both tubes for side A even if only one blew? These are Mesa Rec 2x12's, they have an output on each cabinet, where I can go 4 ohms from one cabinet to output of cabinet A to cabinet B. However I just prefer to just plug both of them in the two 4 ohm jacks on the amp. Last question..... I also have a 16 Ohm 4x12, it's only 8 Ohm's if ran in stereo and I don't want to run it in stereo. So let's say on side A I have two Mesa 2x12's 8 ohms going into two 4 ohm outputs. On side B I want to run one 4x12 16ohm cabinet, but there is no 16 ohm output on the Mesa fifty/fifty. Is it safe to even plug it in there? I don't typically use it but would like to know. Link to comment Share on other sites More sharing options...
Members WRGKMC Posted September 19, 2016 Members Share Posted September 19, 2016 If I did want to plug a cab into the second channel, two 8 ohm cabs, I'd just go 8 ohm in channel 1 and 8 ohm in channel two right? Yes... Then there is this question.... Instead of lugging around two tube power amps, if I'm only using one side, let's say a tube blows on side A, can I then just turn the volume down to zero, remove the tube that blew and switch the cabs to side B? Or do I need to remove both tubes for side A even if only one blew? No. Both sets of tubes work off the same power supply. When a channel blows its for a serious reason and you shouldn't operate the head when somethings gone wrong. You should ALWAYS power down and fix the issue and not continue to run it even if one side seems to be working because it can continuer to blow more components and wind up being a much more serious and expensive problem to fix. I'm not familiar with the repair of that particular head but tubes don't normally just blow without taking other components out. Red plating is often a sign of blown screen/grid resistors. Sometimes you get a degrading of sound quality, crackles and pops etc. I'd double check the manual and see if its OK to run the head with a channel having no load. This isn't normally good for tubes whether you are passing a signal or not. The voltage is still on the tube and it still conducts. If you cant find it printed I'd at least get a large ceramic 4 or 8 ohm resistors connected to a 1/4" jack and keep it plugged in. Better safe then sorry. Link to comment Share on other sites More sharing options...
Members DeepEnd Posted September 19, 2016 Members Share Posted September 19, 2016 . . . I'd double check the manual and see if its OK to run the head with a channel having no load. This isn't normally good for tubes whether you are passing a signal or not. The voltage is still on the tube and it still conducts. If you cant find it printed I'd at least get a large ceramic 4 or 8 ohm resistors connected to a 1/4" jack and keep it plugged in. Better safe then sorry. According to the manual, it is: If you opt to use only one channel of the Fifty/Fifty with speakers connected to only one channel's output(s), you must turn the unused channel's Level control to zero! Otherwise the channel will be operating without a load, and damage to the tubes and/or the transformer will result. Link to comment Share on other sites More sharing options...
Members WRGKMC Posted September 22, 2016 Members Share Posted September 22, 2016 That may well be so but there's still bias on the tubes and the worst thing you can do to a tube amp is run it with no load. That's why I'd rather be safe then sorry. Moving an amp around its easy to accidentally twist a knob setting and you'd never know it was cranked up by accident. Maybe they get around it by using a switched resistor on the output jack. Mesa is pretty innovative when it comes to their gear. They may have added that option to make it dummy proof. I'll have to look at the schematic however. If there's nothing there, and I owned the amp $3 for a 1/4" jack and resistor would let me sleep good at night. I've done enough amp repairs in one lifetime and could do without having to repair my own gear. Link to comment Share on other sites More sharing options...
Members DeepEnd Posted September 22, 2016 Members Share Posted September 22, 2016 I don't pretend to know more than the people who designed and built the amp. That's your department. Link to comment Share on other sites More sharing options...
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