Need to install grounded power cable - advice

[freepressright]

I am working on my second amp and need to install a grounded power cable on it. But it has a fuse holder and an accessory outlet, I'm confused about where each wire needs to go. Can someone look at the pic and give me some advice.

Thanks!

[JHow]

Is this what you are after? Hooking up power cord and convenience outlet? This scheme makes use of the "ground" switch that you find on old amps.

Install - 3 Prong Power Cord on a Vintage Fender Amp | Guitar Files(TM)

Basic idea is to run hot (black) to fuse to power switch to transformer primary back out to other side of transformer to switch, and back to the neutral (white) line. Green gets bolted (use star washer or locknut) to chassis for ground safety. On the outlet in the above, brass is for hot and silver color is for neutral. Outlet is wired across the black and white lines (parallel). On your outlet, if polarised, the wider slot, for the wider blade will be for the neutral line.

Honestly, though, why would you fool with the convenience socket? I would disconnect it and the "ground" switch and just leave them in place so you don't have to look at a hole in your amp. You could re-purpose the switch to do something you want in the circuit - like maybe siwtch in or out NFb, etc.

Re: your picture, you need to clean up the old circuit, before you re-wire. If those big orange caps are caps from line to ground, that has to go with a three-wire plug.

I would recommend a DPDT switch and switch both hot and neutral. Not sure what you have in there now, maybe only SPST.

Also note, regarding that style fuse holder, black goes to the tip, to prevent shock if you try to change fuse when plugged in (never do that!).

Maybe before you solder, draw a picture for yourself and see if it works logically.

[freepressright]

Is this what you are after? Hooking up power cord and convenience outlet? This scheme makes use of the "ground" switch that you find on old amps.

Install - 3 Prong Power Cord on a Vintage Fender Amp | Guitar Files(TM)

Basic idea is to run hot (black) to fuse to power switch to transformer primary back out to other side of transformer to switch, and back to the neutral (white) line. Green gets bolted (use star washer or locknut) to chassis for ground safety. On the outlet in the above, brass is for hot and silver color is for neutral. Outlet is wired across the black and white lines (parallel). On your outlet, if polarised, the wider slot, for the wider blade will be for the neutral line.

Honestly, though, why would you fool with the convenience socket? I would disconnect it and the "ground" switch and just leave them in place so you don't have to look at a hole in your amp. You could re-purpose the switch to do something you want in the circuit - like maybe siwtch in or out NFb, etc.

Re: your picture, you need to clean up the old circuit, before you re-wire. If those big orange caps are caps from line to ground, that has to go with a three-wire plug.

I would recommend a DPDT switch and switch both hot and neutral. Not sure what you have in there now, maybe only SPST.

Also note, regarding that style fuse holder, black goes to the tip, to prevent shock if you try to change fuse when plugged in (never do that!).

Maybe before you solder, draw a picture for yourself and see if it works logically.

I don't want to keep the accessory outlet on the back. It can be cut out of the equation all together.

As for those orange caps, did you mean that I can do away with them?

And as for selecting a DPDT switch, is there a particular rating I should look for?

[JHow]

I wrote DPDT but DPST is sufficient. Something like 15A 125VAC should work.

Maybe like this one...mouser 691-2GK50-73

2GK50-73 Carling Technologies Toggle Switches

Regarding the orange caps, it is always hard to tell looking at pictures, but it seemed to me that at least one of those ran from the convenience outlet (so, either hot or neutral line) and then to the chassis via a ground lug. Usually this is a .05u 600V cap and was a feature of many many old power supplies. You don't need that with the three wire plug and should remove it. You should have no connections between your lines and the chassis, only the single green wire from your plug.

[JHow]

A couple other considerations on power cord:

Use a strain relief on chassis, so if the cord gets yanked it doesn't pull loose while plugged in.

Set up the wires so that green is longer than black and white, so if your strain releif fails then the green will be the last one to come loose and break. Similarly, black should be shorter than white.

I took another look at the picture and it looks like maybe your old cord went to the dual tag strip and then both orange caps went to chassis ground (?) It looks like the tag strip holds the remnants of brownish rubbery power cord? If so, then both caps can retire.

[freepressright]

A couple other considerations on power cord:

Use a strain relief on chassis, so if the cord gets yanked it doesn't pull loose while plugged in.

Set up the wires so that green is longer than black and white, so if your strain releif fails then the green will be the last one to come loose and break. Similarly, black should be shorter than white.

I took another look at the picture and it looks like maybe your old cord went to the dual tag strip and then both orange caps went to chassis ground (?) It looks like the tag strip holds the remnants of brownish rubbery power cord? If so, then both caps can retire.

The two leads of the old power cord went directly to the tag strip. A brown wire runs from the right terminal of the tag strip to the right terminal of the accessory outlet. The left lead of the tag strip has a wire that runs to the switch and then looks like it turns around and comes back to the left lug of the accessory outlet. The center lead of the fuse holder has a bluish black wire that connects up to the left lead of the accessory outlet.

So, cutting through all the BS wiring, how can I simplify this and just add a three-wire power cable and get rid of the functionality of the accessory outlet while utilizing the fuse?

Thank you for all your review and help on this matter. I greatly appreciate it.

[JHow]

Okay, here are the steps in short order:

1. Install strain relief on cord
2. Ditch the caps from the dual tag strip, there should be nothing on it now
3. Move the yellow and black transformer primary to one side of the tags strips
4. Move the black transformer primary to the other side (these look like they are on the outlet)
5. Attach black "hot" wire from cord to the tip of the fuse holder, remove whatever is attached to tip.
6. Attach one long wire from switch to the side of the fuse holder, run the other switch wire back to the dual tag strip and attach on the same lug as black/yellow transformer primary.
7. Attach the white "neutral" wire from the power cord to the other tag strip lug where you have the black transformer primary.
Install ring terminal on the green power cord wire and bolt to chassis on its own separate location - you may need to drill a hole.

At this point, you should have nothing connected to the convenience outlet, nothing on the tag strips except for two leads from transformer (on on each side), the lead from the switch on one side and, and the white wire from the cord on the other.

I am assuming that the orginal switch has only two poles (spst) and I am pretty sure I got the transformer primary leads correct, but if you can tell me where the black one goes,that would help.

Take a look at this guy's set up. You can see the runs (simplified) in one place, except he didn't bolt the green wire to the chassis.

http://music-electronics-forum.com/t18366/


Or look here, scroll down to power transformer hookups to see the circuit diagram. His transformer has black and white primaries, Yours has black and what looks like yellow/black.

Common hookup info

If any of this seems too much, maybe you have a buddy that assist?

[freepressright]

Here's a different view where you can see the switch better. Can you look over this and see if anything needs to change with regard to your advice. Thank you very much!

[JHow]

Switch is what I expected. I can also see the black lead from the transformer on the lower lug of the tag strip. I also noticed black and brown lines running from outlet down off the page. Can you tell where those go?

I am attaching the most basic hookup I could manage with the items you have. There should be no other necessary connections when you are done. No caps to ground, no connections to the outlet. The mystery brown and black wire are not involved, unless there is something like a 120VAC pilot light that we haven't talked about.

[freepressright]

The black and brown wire hooked into the accessory outlet go to a tube-socket labeled "PHONO MOTOR." I have used this amp with the old power cord that I cut off and it works without anything hooked into this odd "PHONO MOTOR" thing. It looks like it can be done away with.

[JHow]

Sounds like you can dispense with that. Just out of curiousity, what was this amp in it's previous life?

[freepressright]

It is a Rauland-Borg model 2035, formerly a PA amp that I converted over for guitar by adding 1/4-inch inputs and speaker outs. It is powered by two 6L6GCs, a 5U4GB rectifier, two 12AX7s in the preamp side, with the phono preamp being driven by a 6AV6.

It sounds quite good as a clean power amp. For overdrive, I run a Vintage Tube Monster, 12AX7-driven preamp pedal. In my pedal I have a BitMo Monstrosity three-way voicing mod that really contours the gain on the pedal to respond like a tube amp's overdrive channel would. In stock form, the pedal's not all that impressive. But modded, it's incredible.

I'm an official artist for BitMo Amp Mods.

I've done my share of solder-in tube amp mods through the years, but just recently graduated to re-capping my first amp this past weekend - a Rauland-Borg 2010, single-ended 6L6 powered former PA head. It's the little brother to the amp I am blogging in this thread about. (see Time for my first recap - Advice sought )

I got them both for free from a Catholic school in southern Ohio. They were going to be thrown away and a friend rescued them from the garbage and brought them to me. I figured them to be the perfect amps for me to learn on, since I had nothing in them money wise.

You, sir, have been a tremendous help to me. I can't tell you how much I appreciate not only your in-depth advice, but also your patience.

I cannot possibly thank you enough.

[JHow]

You're welcome. Be careful. Check your work.

Cool history about the amp - and what a good friend you have. You definitely want to encourage friends who will bring you old amp parts.

[freepressright]

New power cable installed to your specifications. Amp powered up and ran beautifully, less the capacitor hum. I think I'm going to have to invest in some new filter caps.

[JHow]

Great news. Filter caps are par for the course - they don't last for ever.