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 Post subject: Plexi v6 PI Low Voltages
PostPosted: Mon Mar 25, 2019 11:17 am 
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Joined: Sun Mar 17, 2019 11:14 am
Posts: 2
Hello, first post!
I built a Plexi v6 and got it working but I have a few questions.

Without the guitar plugged in the amp is very quiet, when I plug-in it sounds fine haven’t turned it up.

There are two checkpoints that have 0 volts I have remelted the Solder, I am at a loss as how I could have zero.

On V3 pin 2 and 7 voltage is low and it hums when I touch the probe to it, it’s the same at the other end of the wire on the board checkpoint. I switched tubes but same results.

On V4&5 pin3 volts are to high ??


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PostPosted: Mon Mar 25, 2019 11:20 am 
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Holy Ghost
Holy Ghost
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Joined: Sun Mar 13, 2005 4:10 pm
Posts: 7375
Location: Brighton, Canada
Nice and neat build.

The layout diagram has an error on it. Those voltages 'bubbles' should point to the 100K plate resistors, not the coupling caps! Sorry about that. The caps will have zero voltages.

Make sure you measure your mains voltage as a reference.

Check you plate resistor values, ground connections, solder connections and swap tubes to see if any of that changes things.

Re: V4&5 pin3 volts too high ?? At 13V I would say you are OK.

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PostPosted: Mon Mar 25, 2019 2:00 pm 
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Joined: Sun Mar 17, 2019 11:14 am
Posts: 2
Sorry when I checked 100K resistors first, had amp on giving bad readings. Re-checked they are 102k and 107k resistance. Checking voltage at the proper point recommended 217 and 220 I have 161 and 172.
Swapping tube’s increased voltage only slightly 1 to 2 V.
Re-soldered some joints for good measure. ( testing resistance from the tail of the resistor to the base of the turret. Is that a definitive way of checking the solder joint)? Checked all resistors to chassis ground all good there.
V3 (PI) I still have concern about low-voltage at.
Pin 2 52v I have 29v
Pin 7 62v I have 28v
Pin 8 75v I have 40v

The amp is loud more volume than I need. I still have yet to install the VRM.


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