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Old 8th February 2012, 02:49 AM   #1
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Question Pine model 203 Tube Amp - hot chassis grounding question

I'm working on an old Canadian made Pine (Paul) model 203 guitar amp that has a hot chassis and am about to install a Triad N-68X isolation transformer. I have studied the circuit and something just isn't making sense to me with regards to grounding. Now I've read "The Plan" website where the guy installs an N-68X in another old guitar amp but still I feel I'm missing something.

To the point...

In the attached picture you can see I have a secondary side live line (yellow arrows) coming off the on & off switch that after a resistor\capacitor combination goes right to the red X on chassis. I have this thought in my head that if I connect the mains ground to the chassis and secondary side's white static wire to the chassis I'm going too make smoke. I've checked continuity from chassis to switch and it's dead but still

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Old 8th February 2012, 02:58 AM   #2
kevinkr is offline kevinkr  United States
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Please put a power cord with ground on this amplifier before you use it, and in conjunction with installing your isolation transformer.

There should be no connection between the mains and the chassis once you install the transformer. Connect the line cord hot (black lead) first to a fuse, then the power switch and then one primary lead of your isolation transformer. The neutral (white lead) from the line cord goes to the other primary connection ONLY.

Ground one side of the secondary of your isolation transformer to chassis and the other side goes to the rectifier and filament string. (Connection removed from non line side of the power switch prior to installing the isolation transformer.)

Moving this thread to I&A since it is a guitar amp. Please note the message at the top of the tubes/valve forum.
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Old 8th February 2012, 04:15 AM   #3
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Thanks Kevin and sorry about where I originally posted this, should have looked up first.

I have it wired like you mentioned, mains hot to a fuse then to a new toggle switch that I mounted in one of the 4 input jack holes. One side of the primary to the new switch, the other to mains neutral. The green is mounted to one of the screws that secures the N-68X to the chassis.

On the secondary side your saying negate the original switch and fuse then connect a line to the chassis and the other to the filament string? This method sounds similar to how the guy that wrote The Plan did it sans the bridge rectifier part.

What about that static shield white wire on the secondary side? What is it's purpose?
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