Supro 1606 small shock when touching speaker and strings??

[texwest]

I'm working on this 1959 Supro 1606 which is basically like a small champ but with a 6x9 speaker.

I replaced the power cord and removed the deathcap and it works great.  Put the green to ground,  white directly to the primary and the black through the fuse and switch.

There is a buzz on Bflat notes so I tuned my b string to bflat and was playing it and touching the tubes to see if they were rattling.  I was starting to think that the noise was coming from the speaker and might be a rub. So I touched the speaker magnet to see if it was rattling and there was a bit of shrieking sound and I felt a mild shock in my right hand touching the strings.  I thought this was really odd so shut down the amp and looked over my work again.

I see that the output secondaries are wired directly to the speaker, but neither of the secondaries are connected to ground.  I measured 2 vac from ground to both leads connected to the speaker.

I also think its interesting that the speaker is having a problem on bflat as this is the pitch closest to 60 cycles.

I'm a bit scared of this mild shock.  So I would like any advice.   Should I try grounding one of the secondary wires coning from the output transformer?

[sluckey]

Should I try grounding one of the secondary wires coning from the output transformer?

yes

[texwest]

I did a little research and found this quote from Randall Aiken on his grounding page that describes exactly what happened.

"Sometimes it helps to ground the common (sleeve) side of the output jack to the chassis even when no global negative feedback is used.  Occasionally, an amplifier will have a high-pitched oscillation noise, or other type noise that will go away if you ground the output transformer common wire at the speaker jack sleeve terminal.   

In addition, there may be a potential for a  small AC current to flow between the floating sleeve and chassis if the secondary is not grounded.  This current is due to  capacitive coupling  in the output transformer, and may cause a mild shock if the speaker plug sleeve and chassis (or guitar strings) are touched while running a signal through the amplifier.  Even though the potential for dangerous currents is low due to the galvanic isolation of the output transformer, the shock can still be annoying.  For this reason, it is best to always ground the common side of the secondary even when no global feedback is used."

[texwest]

Interesting,  The Bflat resonance noise was eliminated by grounding one lead of the OT secondary. Problem solved.  thanks

[PRR]

I believe electric code "requires" the secondary be bonded to chassis, to divert electric shock, regardless of audio function.

Many of my older radios don't even have a 2nd secondary lead, it is tucked in the OT frame which is riveted to the chassis. (Likewise at the speaker, of course.)

But I know this was not always enforced.

[texwest]

I believe electric code "requires" the secondary be bonded to chassis, to divert electric shock, regardless of audio function.

Many of my older radios don't even have a 2nd secondary lead, it is tucked in the OT frame which is riveted to the chassis. (Likewise at the speaker, of course.)

But I know this was not always enforced.

PRR, you think this could have been a mistake by the factory when it was built?