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Mesa 50/50 modification

2/23/2000 6:32 AM
Mesa 50/50 modification
I need advice regarding some modifications to my power amp. I bought it used and the previous owner had changed the fan and changed the pots. It is wired for 110 volts, (I am in 240V country). I will need to get that changed sometime, but my main problem right now is that I only have a mono 2*12 cab, and I have a stereo power amp. I want to install another standby switch, so then instead of running the ounused channel on zero, and risk damaging the amp in the long term. I figure this is probably beyond me doing it myself, but should it be relatively inexpensive to have a tech do it??  
LWH / Xplora / Mesa Man
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2/23/2000 10:36 AM

The mod is easy, the harder is to add the other standby switch to the chassis (specialy if you want to match the cosmetics of the original switch).  
There's another option: you can wire your 2x12 cab so that it can work in stereo or mono.
2/23/2000 5:23 PM

LWH / Xplora / Mesa Man,  
I use to have one of these. I occasionally had situations that would only allow or require the use of one side of the amp.  
I inquired with Mesa tech service and here's what they told me.  
That it was OK to use only one side of the amp as long as there was nothing plugged into the input jack of the channel that's not being used.  
I followed their advice and never had any problems.  
Don't take my word for it though, I would encourge you to speak directly with their service department to confirm this information.  
2/24/2000 3:52 AM

When I had one of these and needed to use it in mono, they told me to do the same with the input jack, but to also turn the volume all the way down and the precense all the way up. I eventually sold the unit and got a Marshall 9100 (50/50, 6L6) which is oddly made MUCH better than the Mesa 50/50. Of cource since this was a well made product, Marshall discontinued it. That's my $0.02 :)  
Oh yeh, I think there's something on the Mesa site that tells you about running their power amps in mono, I could be wrong though, but worth checking out.
2/25/2000 1:09 AM
Don Symes

They've got a lot of their manuals online, too.
2/25/2000 3:37 PM
Stephen Conner
Standby ain't always good
Hi folks,  
Not a lot of people know this... but leaving tubes for a long time with heaters on but no cathode current (ie in standby) is as bad for them than leaving them powered up! This is because of an effect called cathode poisoning. The standby switch is only meant to be used for powering up, and for short breaks.  
Don't bother with that extra standby switch, instead you might want to pull the power tubes in the spare channel out.  
Steve C.
2/27/2000 2:53 AM
Carl Z

I like to jumper my standby switch with an orange drop in the range of 0.047uF This lets a few volts of current through and never shuts the tube off completely. Just cuts it down to almost nothing. No pops either when i flip the switch! :)  
Carl Z

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