Need advice on wiring variac switch

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bmf5150
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Need advice on wiring variac switch

Post by bmf5150 » Thu Jan 29, 2015 1:05 pm

Well I decide I wanted the variac switch in my amp that drops everything including the heaters just like the suhr sl68 and George's amp does.i have heyboer power tyranny with the extra 150v primary to do so..here is the wiring layout below that I came up with.just want to make sure it's correct,get your guys opinion..

Here is my power tranny wire color code
Primary
white-0,black-120, black/white-150
Secondary HV
red-185, red/blue-152, red/yel-0, red/blue-152, red-185 @ 280mA.
bias
blue-0 blue-100v wound w/ same wire as HV, 280mA
fil
grn-3.15, grn/yel-0 , grn-3.15 @7.5 Amp


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VelvetGeorge
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Re: Need advice on wiring variac switch

Post by VelvetGeorge » Thu Jan 29, 2015 1:50 pm

Wire it like this:


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george
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bmf5150
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Re: Need advice on wiring variac switch

Post by bmf5150 » Thu Jan 29, 2015 2:02 pm

Thanks George,one last question,how do I incorporate the light to the switch.my indicator light is 120v off the switch
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VelvetGeorge
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Re: Need advice on wiring variac switch

Post by VelvetGeorge » Thu Jan 29, 2015 2:06 pm

The top white wire terminal and the black wire from the PT (120V) terminal.

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bmf5150
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Re: Need advice on wiring variac switch

Post by bmf5150 » Thu Jan 29, 2015 2:11 pm

For bias,do you have to bias the 120v switch position first then the 90v variac mode second?
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VelvetGeorge
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Re: Need advice on wiring variac switch

Post by VelvetGeorge » Thu Jan 29, 2015 2:39 pm

Yes, bias in normal operation first. Then switch variac mode and bias for that.

george
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bmf5150
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Re: Need advice on wiring variac switch

Post by bmf5150 » Thu Jan 29, 2015 2:50 pm

Thanks George
R.I.P My precious daughter Aubrey Marie May 20th to May 23rd 2006,we love and miss you!
My EVH sound clips.
http://soundclick.com/share?songid=7782093" onclick="window.open(this.href);return false;

bmf5150
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Re: Need advice on wiring variac switch

Post by bmf5150 » Fri Jan 30, 2015 2:25 am

One last question George,the bias pot on the board controls the standard mode correct,but when switching to variac mode the bias pot on the switch interacts with the one on board??wouldnt the 150v tap primary be on the same side as the bias pot on the switch???
R.I.P My precious daughter Aubrey Marie May 20th to May 23rd 2006,we love and miss you!
My EVH sound clips.
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vh junkie
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Re: Need advice on wiring variac switch

Post by vh junkie » Fri Jan 30, 2015 3:23 am

The two pots are supposed to interact. The switch mounted pot is shorted out (bypassed) in HIv mode. That is when you adjust the bias on the board for proper HIv bias. Then for LOv mode you leave the board bias pot alone and adjust the switch bias pot for proper LOv bias. At this point, the two pots are in series.
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bmf5150
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Re: Need advice on wiring variac switch

Post by bmf5150 » Fri Jan 30, 2015 3:32 am

Thanks Robert
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Re: Need advice on wiring variac switch

Post by VelvetGeorge » Fri Jan 30, 2015 8:48 am

Exactly.

Think of it as the switch adds more resistance in series for variac mode. This lowers bias voltage, increasing bias current in the tubes.

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Re: Need advice on wiring variac switch

Post by bmf5150 » Fri Jan 30, 2015 9:53 am

Thanks for the explanation George
R.I.P My precious daughter Aubrey Marie May 20th to May 23rd 2006,we love and miss you!
My EVH sound clips.
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RagnarMarGunn
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Re: Need advice on wiring variac switch

Post by RagnarMarGunn » Tue Feb 10, 2015 2:53 pm

George and all, what is the required rating in amperage for the switch ... and if someone could explain why, the fuse before power switch in 100W MV is rate 4 amp. I need to do this mod on my Metro 100W MV an would like have a switch that is as small as possible, so basically i'll need DPDT before standard power switch which is the Marshall one, just to select between 220vac & 240vac on one side and bias on other. That selection would be done with Marshall power switch off.
Regards
Ragnar Már

'67 JMP 50W
'82 JCM 800 1959
'83 JCM 800 2203
'87 2554
'09 Metro JMP 2204
'10 SDM 2550X
'10 Metro JMP 2203

RagnarMarGunn
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Re: Need advice on wiring variac switch

Post by RagnarMarGunn » Tue Mar 17, 2015 7:16 am

No worries, have it figured out, Variac wired on my Metro 2203 Friedman BE-100 Specs with some of my own twists, sounds great.
Regards
Ragnar Már

'67 JMP 50W
'82 JCM 800 1959
'83 JCM 800 2203
'87 2554
'09 Metro JMP 2204
'10 SDM 2550X
'10 Metro JMP 2203

jloewenheim
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Re: Need advice on wiring variac switch

Post by jloewenheim » Sun Jan 05, 2020 5:40 pm

George, any chance you can repost your diagram of how you wired the variac switch? For some reason, that link does not seem to work.

Cheers
Jake

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