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Posted: **Sun Sep 28, 2008 5:38 pm**

today i was messing around with my amp (traynor)when it was plugged into the variac. as i was holding my guitar, i reached for the variac to move the dial, and my finger brushed the variac chassis...i got a good tingle. so i got the MM out, and tried the amp chassis direct to the variac chassis- full voltage! the voltage measurements change in step with the variac dial, too...
then i flipped the "ground" switch that is on the back of the amp, and tried another measurement. this appeared to bring the voltage down into the millivolt range. it also made the amp a tiny bit quieter.
so, should i always leave the "ground" toggle in the up position? should i consider removing the ground toggle? as far as i know the outlet is wired correctly. the amp is from '74 and has a 3-prong plug.
i am thankful that i didn't grab the amp chassis and the variac at the same time or i guess i would have gotten 120v right across the chest; wonder what kind of current could travel through that path?
and i'm one of these people with clammy sweaty hands, so someday i'm gonna get a ripper if i keep playing around with these old amps

Posted: **Mon Sep 29, 2008 2:51 pm**

Hmm... If there is a 3-prong plug on the amp, the ground switch on the amp should have no effect unless the ground wire in the line cord is not connected to the chassis (or it's not actually getting grounded through the variac or outlet). Easy enough to check the amp with an ohmmeter. Does the variac have a 3-prong plug and outlet? Could also be a problem with the ground on the variac. Lastly, hopefully the outlet ground is really grounded. I've actually found an outlet like that in my house.

Posted: **Mon Sep 29, 2008 6:03 pm**

There was a very short time when amps had both the grd switch and a 3 way plug. When the plugged into a grounded outlet the chassis should be grounded and the grd sw should not have any effect. So the upper post is correct and maybe the variac is not wired to ground?? I'd actually pull the wall socket and inspect, then the variac, then the amp.... One of those is wired wrong.... Take your time and think it out.... You also had loads of wonderful help here!

Posted: **Mon Sep 29, 2008 9:06 pm**

The so called "ground switch" toggles a .047 mfv 630 volt capacitor from one side or the other of the power line to ground. I guess when you
had the "hot side" of the line bleeding to ground, and the Variac was
maybe not grounded, you had enough leakage through the capacitor
to give you a tingle. Not good.

here is a schematic if anyone wants to take a look ...

http://www.lynx.bc.ca/~jc/721020_YGL3_3A_Mk3.gif

Posted: **Mon Sep 29, 2008 11:19 pm**

Is your power cord a 3 wire cord? I played through a Fender Bassman for years with a three prong plug that had not green wire in the cord. Eventualy figured why singing backup vocals could be shocking (vocal prowess aside) and felt like a total dumbass. Many a cord cap has been replaced and since most of them have three prongs they tend to mislead.

Posted: **Tue Sep 30, 2008 10:21 am**

Look at the output section, see anything unusual? Garnet and Traynor discovered if you put pin 1 of EL34s to the bias voltage it increased the output tubes lifespan substantially. I have bee doing this in all my amps as well. I haven't seen it anywhere else tho.

Don

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my amp still scares me

my amp still scares me