Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Oddvar on September 24, 2019, 03:53:06 am
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Hi. I wonder if I have to change the MOV cap (resistor?) in a Mesa that I have changed the transformer from 117v to 240v?
I also wonder if there is a way to fix the ground button on the back, (it has a middle position and a "A" and "B") to a permanent middle position, since this button type is illegal in my country?
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The MOV continuous operating voltage should be at 20% above maximum system voltage under normal conditions.
Simply disconnect the capacitor from the ground switch.
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> in a Mesa
> fix the ground button
MESA made hundreds of amplifiers. Does this one have a name/model/number?
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> in a Mesa
> fix the ground button
MESA made hundreds of amplifiers. Does this one have a name/model/number?
It's a Mesa Caliber 50, from around 1989/90.
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looking at this schematic (from a US point)
https://el34world.com/charts/Schematics/files/Mesa_boogie/Boogie_50cal.pdf
IF I didn't want the switch/cap, appears they can be removed just fine, 240vac guessing the same, doublecheck, or move where there is less Govmnt involved with tube amps :icon_biggrin:
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I wonder if that pilot light is a 115V type or a 110V to 220V type.
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Remove the ground switch and its cap.
There is no MOV on that schematic but you show one in your picture. Find a 260V-300V MOV (local standard) and put it on the PT side of the power switch.
The neon pilot light *may* work OK, for a while, on double voltage. When it fails, get one rated for 230V.
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I have found a Mesa replica indicator light 240v on the TAD site. Mesa parts are almost impossible to get here. Very annoying that Mesa has all the part in their online shop, but if you want to buy from them, you must contact distributor in Finland, and they must redirect to Norway which again never respond.
The A_B switch is visible in the picture, but I am not sure how to disable it, given that a friend of mine who is a certified Mesa repairer, advised against it. Any advise?
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The A_B switch is visible in the picture, but I am not sure how to disable it, given that a friend of mine who is a certified Mesa repairer, advised against it. Any advise?
Does this amp have a three wire power cord with one wire connected to earth/chassis ground? If so, there is no need to disconnect it.
But if you insist, just snip the gray wire and tape the end.
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The A_B switch is visible in the picture, but I am not sure how to disable it, given that a friend of mine who is a certified Mesa repairer, advised against it. Any advise?
Does this amp have a three wire power cord with one wire connected to earth/chassis ground? If so, there is no need to disconnect it.
But if you insist, just snip the gray wire and tape the end.
It has a three way cord, one to ground.