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Thread: Randall RG-120-210 Power Switch?

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    Randall RG-120-210 Power Switch?

    I have an RG-120 with a broken power switch. I am trying to understand this switch configuration. I have found the following (attached schematic) on this forum.

    For now I just want to jump the switch to see if the amp is working. If I am reading the schematic correctly, it looks like both the hot and neutral are both switched? What is that X pattern in the switch doing?

    Thank you. MarkO
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    Supporting Member The Dude's Avatar
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    The X pattern is switching polarity. There is a "death cap" on one side of the AC input. The switch decides whether hot or neutral is connected to that cap. It's like the old separate polarity switch, but done with the power switch.

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    So was this originally a 3 position switch? This switch is completely destroyed. It has 4 connecting tabs on the outside and 6 contact points on the inside.

    Trying to determine a replacement switch.

    Thank you

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    Quote Originally Posted by misterc57 View Post
    So was this originally a 3 position switch?
    Yes, Center Off three position. ON/OFF/ON

    You can replace it with another three position switch or just a normal D.P.S.T. ON/OFF one. Just be sure to remove the chassis ground cap and install a three wire ac cord.

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    Odd to me... it has a 3 prong AC cord from the factory, as well as a 3 prong convenience outlet in the back. The chassis ground cap is connected to the neutral (white) side of the mains. Does this make any sense?

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    Old Timer J M Fahey's Avatar
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    Since you will junk the .01 death cap anyway, just use a far easier to source DPDT one as suggested by 52 Bill.

    Each half just switches hot and neutral wires respectively.

    EDIT:
    The chassis ground cap is connected to the neutral (white) side of the mains. Does this make any sense?
    *Maybe* they wanted to cover the case of users in an old house/club with old style 2 prong outlets (I bet Millions remain) using a 3-to-2 adapter ... or plain chopping the ground lug (have seen it many times) , and still providing *some* "noise grounding".

    Remember itīs a 40 year old amplifier and I bet way back then ungrounded home wiring was even more abbundant.
    In that case the phase inverting switch might have been useful.
    Seen same thing in not so old Peavey amps, go figure.

    Canīt imagine any other explanation.

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    Last edited by J M Fahey; 02-09-2019 at 07:34 PM.
    Juan Manuel Fahey

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    Another observation in this amp. There is a circuit breaker instead of a fuse. This breaker is wired on the neutral side (although the schematic shows it on the hot side).

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    Lifetime Member Enzo's Avatar
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    I would suggest that with that cross wired DPDT switch, there is no hot and neutral you can rely on. Flip the switch one way you have them, flip the switch the other way, they are reversed.

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    I plan to eliminate the X pattern and remove the ground cap. Also thinking I could hard wire the neutral side and then use a SPST on the hot side as an ON/OFF. Thoughts on that?

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    Old Timer J M Fahey's Avatar
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    Maybe, but it really costs nothing using a DPDT so why not?

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    Quote Originally Posted by J M Fahey View Post
    Maybe, but it really costs nothing using a DPDT so why not?
    Primarily because I have a SPST on hand.

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    [shrugs] ...

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