Power cord conversion

[eschertron]

The last version of the UL safety regulations concerning "commercial audio visual equipment" considered soldering an acceptable way to bond the chassis to the earthed conductor, however, they required that the green(yellow-green in Europe/Britain) wire have have it's own dedicated, additional strain relief to keep the wire from vibrating or moving. This is a wise practice anyways because a proper solder connection is a very reliable mechanical and electrical connection. The weakness of a solder connection is at the junction of where the wire and solder meet. Any movement in the wire causes stress at this point and there is risk of breaking. Risks increase overtime as oxide builds up on the conductors and wire insulation becomes more brittle.

I understand the effects of work-hardening on the wire, but I'm having a difficulty visualizing what a strain relief might look like for that application. Can you describe some specific examples that you have seen? Sometimes specifications (have it's own dedicated, additional strain relief) are written to be deliberately vague. Thanks.

[SoulFetish]

I understand the effects of work-hardening on the wire, but I'm having a difficulty visualizing what a strain relief might look like for that application. Can you describe some specific examples that you have seen? Sometimes specifications (have it's own dedicated, additional strain relief) are written to be deliberately vague. Thanks.

Well that's an interesting question. I can't say I remember a seeing an example exactly as described above. But, for example, Roland used what I would guess is a similar technique in the older Jazz Chorus amps. Except they used an additional strain relief for all 3 wires inside the chassis, rather than just the earth conductor.
I always imagined something like this would work with a #6 or 8 machine screw:

[bsco]

I found some information that indicates that the Kustom Charger used the PC5033 power amp. Copy attached. The power amp drawing includes the power supply but the one I found does not show a death cap at all. In addition it shows a box labeled TB1 to depict the ON-OFF switch so we can't see the wiring details. Go figure?
There may be other versions of the drawing. You could check for the PC number actually used in your amp. It would be interesting to know. Otherwise, I would just buzz out the wiring and verify that the output connections from the power switch are direct to the PT primary and nowhere else. Would be interesting to post pictures if you can.
[ATTACH]50377[/ATTACH]

OK Tom. I got some pics...I had hurt my back and had to take muscle relaxers for awhile......I was in hard shape.....very, very painful...anyway I am feeling much better...I didn't lift anything...I was bent over and stood up and that was it.....anyway check out these pics.....
Cheers

[bsco]

I found some information that indicates that the Kustom Charger used the PC5033 power amp. Copy attached. The power amp drawing includes the power supply but the one I found does not show a death cap at all. In addition it shows a box labeled TB1 to depict the ON-OFF switch so we can't see the wiring details. Go figure?
There may be other versions of the drawing. You could check for the PC number actually used in your amp. It would be interesting to know. Otherwise, I would just buzz out the wiring and verify that the output connections from the power switch are direct to the PT primary and nowhere else. Would be interesting to post pictures if you can.
[ATTACH]50377[/ATTACH]

OK Tom. I got some pics...I had hurt my back and had to take muscle relaxers for awhile......I was in hard shape.....very, very painful...anyway I am feeling much better...I didn't lift anything...I was bent over and stood up and that was it.....anyway check out these pics.....
Cheers

[Chuck H]

The heaviest lifting I do when I'm told not to lift anything is 12oz. Then 11oz., 10oz... etc. Repeat as necessary.

[Enzo]

My heart doctor told me not to lift anything heavy, so now I have to sit down to pee.

[SoulFetish]

My heart doctor told me not to lift anything heavy, so now I have to sit down to pee.

Boom!

[Tom Phillips]

My heart doctor told me not to lift anything heavy, so now I have to sit down to pee.

But you could still lift a vintage SVT head on to the bench! Right?

[Enzo]

Well, sure, with my OTHER hand...

[Chuck H]

Thank you ladies and gents. Enzo is here all week. Remember to tip your waitress.

[bsco]

I was thinking about this again...Why can't I remove the switch and death cap, install a single throw double pole switch, install the white and black wires on one side of the switch and install the corresponding white and black wires on the other side of the switch and connect the safety ground wire to the chassis.....that way, both live and neutral will be switched either ON or OFF at the same time.......and there would be no need for the cap.....and no need for the power/polarity switch......Any thoughts?? comments??
Cheers

[Chuck H]

That's fine. And I think think that's been implied in some posts above already. That's the way most modern builders do it, switching both hot and neutral AC. You still want to fuse on the hot lead. I've built with just switching the hot AC and I think that's pretty much ok. Millions of amps have been built that way. The exception being that sometimes some bar or club owner wants to save some money, fancies themselves as a handyman and installs some AC outlets in reverse polarity. It happens. But even then the amp is no more dangerous when on than if it were wired with the double pole switch. But when off, and only if there is a fault in the amp shorting the hot AC lead to the chassis and only if the amp is plugged into a reverse wired AC outlet is there additional danger over the double pole switch. Apparently having everything go wrong at the same time doesn't come up very often because guitar players haven't been regularly electrocuted by those amps with the single pole power switch. So "I" wouldn't have a problem using the existing switch, switching only the hot lead and just having the other switch throw not do anything. Other's here will definitely disagree.

[bsco]

Just getting back to myself..I had hurt my back a couple of weeks ago and had to take muscle relaxers....and they made me very light-headed so I didn't touch anything...and while that was going on, My ears got clogged up and couldn't hear anything.....got everything all straightened away and I am back at this amp for a friend of mine....I decided to just plug in the amp and check the voltage on the chassis to house safety ground.....120 something volts when the polarity switch is in one direction and 2.9 volts in the other.....I have to pick up a dpdt power switch for this before the weekend.....just wanted to run this particular finding by you guys........
Cheers

[Chuck H]

That seems right. In one switch direction the hot AC mains lead is connected to the chassis via the "death cap". The death cap passes AC. I assume it's relatively small value mitigates dangerous current, but now what if that cap shorts!?! That's why they call it a death cap. The same motivation for changing to a grounded AC mains cord with a safety ground still applies.

[bsco]

That seems right. In one switch direction the hot AC mains lead is connected to the chassis via the "death cap". The death cap passes AC. I assume it's relatively small value mitigates dangerous current, but now what if that cap shorts!?! That's why they call it a death cap. The same motivation for changing to a grounded AC mains cord with a safety ground still applies.

the cap value is .022 at 150VAC.....