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PostPosted: Sat Dec 30, 2017 5:04 am 
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Bottle Rocket

Joined: Sun Dec 03, 2017 11:37 pm
Posts: 4
Boogiebabies wrote:
If it's R123 thats bad, it's the dropper resistor parallel R401 to the plate voltage when in R1 and R2.

That cap and VR are for the footswitch, or low voltage circuits.

PM me you email address and I will gladly send you a IVB schematic, but my opinion is that you should send the amp to Mesa. Those PCB's are really touchy when it comes to repair.



Hi,

sorry to revive this old thread.
I have some problem on mk4B also, but it's about the R124, according to the schematics, it's 6,7 Ohm to drop 15v to 12v. but without the wattage info. mine have been replaced, with a dale resistor 9 ohm 5 watt resistor but i check the temperature on this reisstor is incrdibly high (+/1 90 degree celcius). can you tell me the original resistor wattage rating was?

only heating the tube will consume about 3 watt. with switching circuit it's about 4.8 watt.

thanks any picture opr help will greatly appreciated,


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PostPosted: Sun Dec 31, 2017 12:11 am 
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Bottle Rocket

Joined: Sun Dec 03, 2017 11:37 pm
Posts: 4
update I already solve this, it's should be rated at minimal 2 watt. mesa wants the brown sound out of the V1. i think...

here is the circuit simulation:

http://tinyurl.com/ycls2dz9


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