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Discussion Starter #1 (Edited)
Hey all. I have 50 with a passive loop. It's basically a JCM800 circuit with a few tweaks, such as 6L6's and a PPIMV. I'm wanting to install the Metro Zero Loss loop in it. Unfortunately i'm in Regina and there are zero amp techs close. I've done some straight forward mods to other amps such as NFB and resonance etc. I'm decent at following directions and working safely, but have no knowledge of schematics.

When I look at the instructions on where to measure the B+ and splice into the PI supply node, the 2203 board in the instructions doesn't match with mine. Can anyone please take a look at the amp gut shot and possibly direct me on where to measure and add the decoupling resistor?



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See how there's a black wire jumper from that node to the junction of the PI plate resistors (82K and 100K)?
That resistor junction is where you want to measure. Can you see it on yours?
 

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Discussion Starter #5
See how there's a black wire jumper from that node to the junction of the PI plate resistors (82K and 100K)?
That resistor junction is where you want to measure. Can you see it on yours?
Thanks for your reply! Yes, right here, right? But there’s no resistor jumpered like on the 2204 board. That’s also where the fx loop splices in to draw its power off of that resistor.



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It looks like your amp has a 22K dropping resistor at the first filter cap where the JCM800 style you have pictured has two 10K resistors in series. Measure between the 100K and 82K PI resistors and each end of the 22K resistor. Whichever end reads 0 ohms is the point you want.

It may not be "pretty" to have wires on top of the board to connect the different nodes but I do prefer doing it that way myself. No surprises for anyone who has to work on the amp after you...
 

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Discussion Starter #7
That’s where it joins for power. And depending on the B+ readings you add the other value resistor in series




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Discussion Starter #8
Also, thanks all for your help. I really appreciate this! I really don’t want to go through the hassle of packing it and sending it to a tech. If I can get some assistance of where the points join I think I can pop it in no prob


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From where those 2 resistors are joined together (that you circled), there is a wire going underneath the board somewhere. To the resistor that Jim Jones mentioned. You can check the resistance with a meter like he mentioned, or you can look under the board where the wire goes.
Do you have any layout diagram that came with your build? If so, post it.
 

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Discussion Starter #10
It looks like your amp has a 22K dropping resistor at the first filter cap where the JCM800 style you have pictured has two 10K resistors in series. Measure between the 100K and 82K PI resistors and each end of the 22K resistor. Whichever end reads 0 ohms is the point you want.

It may not be "pretty" to have wires on top of the board to connect the different nodes but I do prefer doing it that way myself. No surprises for anyone who has to work on the amp after you...
Thanks!! If the loop just enters in series with that resistor, could I also just splice it into where the 100k and 82k join?


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Yes, the point where those 2 resistors join is the same point as shown on their drawing. You can connect to that turret circled in epis post above (#4).
Unless I'm missing something, as I'm a bit confused about you using the word 'series'. But you are supposed to measure the voltage first, correct?
 

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Discussion Starter #13
Yes, the point where those 2 resistors join is the same point as shown on their drawing. You can connect to that turret circled in epis post above (#4).
Unless I'm missing something, as I'm a bit confused about you using the word 'series'. But you are supposed to measure the voltage first, correct?
Yes, I am. Sorry, by series I mean this resistor from the loop enters the amp board in series to that resistor



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