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> Help: Want to add a grounded power cord
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rowka
Junior tube assistant
Posts: 1
(5/22/05 3:57 pm)
Reply Help: Want to add a grounded power cord
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to my old Traynor YBA-3 amp. The amp was originally supplied with a non-polarized two-prong power cord and I want to make it safer.
Here is a schematic of the amp.
www.lynx.bc.ca/~jc/721005_YBA3.gifThe power supply portion is there in the upper left of the drawing.
I intend to connect the ground to the power transformer's bell attachment inside the chassis.
How should I connect the hot and neutral legs? Does it matter? Hot on the switch, neutral on the CB? Hot on the switch and CB?
Also, upon further observation, I noticed that I have to replace caps soon as there are blisters starting to form on the end caps.
rowka
Junior tube assistant
Posts: 2
(5/22/05 4:08 pm)
Reply Re: Help: Want to add a grounded power cord
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Of the caps that need replacing are two cans that hang from the chassis with the cans soldered to the chassis as both an electrical ground connection and as a mechanical attachment.
I copied the info off the label:
Sprague Electronic Capacitor
85o CTVL 1630
80uF 350VDC
Can Neg 7504L
I haven't found one in the same configuration. Will I have to just get a different type with a similar rating and mount it inside the chassis?
Thanks
PHATamps
I only work on tube amps
Posts: 479
(5/22/05 4:43 pm)
Reply Re: Help: Want to add a grounded power cord
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For the power cord, I would do as shown in the schematic and connect the hot (black) wire to the C/B and the neutral (white) wire to the switch. I'm sure there are those who would disagree and insist that the hot should go to the C/B and the switch in series, and the neutral directly to the PT, but I've never understood why it would be unsafe to do the former.
As for the caps, the cheaper, and maybe easier way to go would be as you suggest; get some individual caps from Doug and tie them down inside the chassis, if you have room. If you don't Antique Electronic Supply manufactures can-type caps and may be able to custom-make a direct replacement.
JayB
Senior tube assistant
Posts: 108
(5/22/05 4:43 pm)
Reply Re: Help: Want to add a grounded power cord
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Connect the new power cord just as it is now but connect the new green earth ground to one of the transformer bolts.
As for the caps, Doug has a 100uf/450V that will work. Always go up in the voltage if you can't find one exact. A little more filtering wouldn't hurt either. IF you must have the exact, check for sprague part number, TVA1716. That's the exact replacement 80uf/450V cap. Doug carries the most common ones. Just like me, you got the odd ones. Try finding 220uf/285V.
Are they can or radials?
The schematic calls for 450V ratings. Why 350V?
rowka
Junior tube assistant
Posts: 3
(5/22/05 4:55 pm)
Reply Re: Help: Want to add a grounded power cord
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Quote:
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Are they can or radials?
The schematic calls for 450V ratings. Why 350V? quote]
My notes say 350 is what it says on the cap itself. I'll double check.
The caps in question are hanging on the left.
rowka.home.comcast.net/tr...back1.jpg" style="border:0;"/>
In this pic, they are in the top right. Hard to see, but the cans are soldered to the chassis at 4 tabs, with a single + lead in the center.
rowka.home.comcast.net/traynor/ins" style="border:0;"/>
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rowka
Junior tube assistant
Posts: 4
(5/22/05 4:56 pm)
Reply Re: Help: Want to add a grounded power cord
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Let me try the pics again.
JayB
Senior tube assistant
Posts: 109
(5/22/05 5:25 pm)
Reply Re: Help: Want to add a grounded power cord
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Ok, their the can ones. I hate those things, so hard to find suitable replacements. Well you could go with the axial ones with no problem. To keep the look of the amp this is what I would propose. Look for the Marshall cap cans. Their multi-sectional so yo would only use one half of each can. They come in 100uf/100uf 450V. Those should work provided the hole diameter they fit in is the same. OR, you could use the F&T 50-50/500v that Doug carries. Just parallel them for 100uf. Cap cans I have found to pretty hard to find. I seen the marshall replacements I believe at antique supply. Just make sure their rated for 450V. Schematic calls for it. Measure the B+ on those caps to see for sure.
Edited by: JayB at: 5/22/05 5:26 pm
rowka
Junior tube assistant
Posts: 5
(5/22/05 5:55 pm)
Reply Re: Help: Want to add a grounded power cord
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I think I will go with axial ones and just mount them inside. I'll disconnect the cans and just leave 'em in there.
Thanks.
rowka
Junior tube assistant
Posts: 6
(5/22/05 5:58 pm)
Reply Re: Help: Want to add a grounded power cord
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What about the "GROUND" switch? Should I do anything to that? Will it matter either way? Whatever position it's in?
JayB
Senior tube assistant
Posts: 110
(5/22/05 7:58 pm)
Reply Re: Help: Want to add a grounded power cord
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Disconnect it. Use this link.
www.unclespot.com/3prongconversion.JPG Keep the 100ohm 10w resistor for the fan.
rowka
Junior tube assistant
Posts: 7
(5/22/05 9:49 pm)
Reply Re: Help: Want to add a grounded power cord
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Thanks again.
rzenc
Junior tube assistant
Posts: 96
(5/23/05 8:40 am)
Reply 220uF Cap
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Jay B: you can try JJ cap...they have a vertical mounting cap rated for 385 Volts and 220uF...maybe you can get it at
www.tubesandmore.com...
HotBluePlates
I only work on Fender's
Posts: 1181
(5/23/05 11:46 am)
Reply switch wiring
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I also recommend wiring the hot wire to the fuse, then to the switch, then to the power transformer, and wiring the neutral to the other side of the power transformer.
Regarding the safety element mentioned above: the transformer doesn't care how you wire it, as it's all the same. However, let's say there's a fault in the amp that causes the fuse/circuit breaker to blow.
If the hot is wired to the fuse/circuit breaker, then the 120v from the wall is only present at the point where hot wire enters the chassis and connects to the fuse holder/circuit breaker.
If instead the neutral is wired to the fuse and switch, then 120v is present at the cord, in the transformer, and on the other side of the switch and/or fuse/circuit breaker. The power will appear to be off, and the amp won't draw power, but if you happen to touch the chassis and be unlucky enough to touch any of these other multiple locations that the 120v is present, you'll get zapped. So it's a shock hazard.
rowka
Junior tube assistant
Posts: 10
(5/25/05 10:17 pm)
Reply Re: switch wiring
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Well, I wired up the grounded power cord as JayB described above and I kept the 100 Ohm resistor-fan between the hot and neut. Installed my cathod resistors. Double checked everything.
Plugged it in and turned it on. Poof. Blew the CB (won't reset) and blew the AC switch (won't close).
Dang.
HotBluePlates
I only work on Fender's
Posts: 1194
(5/26/05 10:05 am)
Reply Re: switch wiring
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There must have been a mistake or a solder drip somewhere. If the cord was wired exactly as it was originally, but adding the green wire bolted to the chassis, then the amp would have worked.
Carefully double check everything.
rowka
Junior tube assistant
Posts: 11
(5/29/05 8:43 am)
Reply Re: switch wiring
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I haven't gotten back to look at it yet, but I susspect I shorted the Hot to the chassis (probably with a solder drip).
I got a new CB and switch and I'm gonna take a real good look at it this morning.
Just to be clear (I'm sure this is the case but want to double check with you knowlegable folks), there should be NO continutiy between the HOT and chassis, and between the NEUT and chassis. Is this correct?
6G6
I only work on tube amps
Posts: 422
(5/29/05 10:22 am)
Reply Re: switch wiring
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That is correct.
The only continuity to the chassis should be the ground.
Tiny Daddy
I only work on Fender's
Posts: 1243
(5/29/05 10:22 am)
Reply Re: switch wiring
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Yes that's correct, absolutely no continuity from either side of the power line to chassis.
rowka
Junior tube assistan
Topic: Help: Want to add a grounded pow &nb (Read 30071 times)