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Old 18th January 2010, 09:53 AM   #11
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Just put your DVM across the output using the ac volts scale. The reading should be quite low low milliamp range. It is not a catch all test but will detect if you have a severe hum issue, it won't catch oscillation though unless you use an osciliscope. It also wouldn't hurt to check them vs. ground on the DC scale in case the secondary is shorted.

I used the big edcor's on my tubelab SE and am very pleased with them as well.
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Old 5th February 2010, 02:30 PM   #12
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Alright, I finally got the chassis done, the stupid metal top plate drilled, and everything installed. I am going through the awesome step-by-step checkout that Ty put together and already hit a snag; on pin 2 of the 12AT7 I'm getting a resistance of 0 instead of the 220K I'm supposed to. On pin 7 of the 12AT7 I do get the 220K reading.

Being an idiot, I went ahead with the rest of the checkout and everything looked good until it came time to plug it in and check the filament voltage on the 12AT7. I went ahead and plugged it in (with the power strip as George suggests as well as having my meter clipped on so I don't have to touch it) and flipped the switch. It made a strange noise, I got a little spark where the power switch meets the mounting plate its attached to and then nothing. I unplugged everything and checked the fuse and it was still intact but I am hesitant to proceed further.

I've checked all my wiring and everything looks good. Also, I can't find anything that burned or popped underneath "the hood" so I think everything is okay. I'm a little worried about the spark at the power switch which makes me think I've got a grounding issue there. The power switch, input jacks, and binding posts are attached to a metal plate that is screwed to the wooden chassis. The input jacks and binding posts are all grounded to my star ground; do I need to ground the switch as well?

I had everything working on the breadboard before I put it in the chassis so I'm pretty sure the board is put together correctly... Any advice is appreciated.
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Old 5th February 2010, 02:43 PM   #13
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It does sound like something is wrong with the switch or the wiring. Do you have any pictures of the area?

Also, it sounds like you might have a short at the tube socket but that alone should not do any harm other than making that channel silent. However I'd inspect for other shorts.

Last edited by rknize; 5th February 2010 at 02:45 PM.
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Old 5th February 2010, 09:57 PM   #14
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Sorry for the delay. Here's the link for the pictures I took, please advise if you need to see anything else.

Picasa Web Albums - jeremyrobertson1 - Simple SE

I can't find anything that looks like a short on the 12AT7 but maybe I'm blind. Seeing where the switches are mounted, do I need to ground that plate and the switches as well? As mentioned above, the RCA's and binding posts are both attached to the star ground.
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Old 5th February 2010, 11:40 PM   #15
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Also, is it possible to toast a power switch? I'm using a pretty beefy NKK switch rated for 2A and 250V; also, I've got the fuse placed in between the switch and the PT. After the little spark I got last night my switch feels a little weird; almost like its easier to switch into the on position than the off position (kind of like the breakers in your circuit box at home). Now, I may just be paranoid and imagining things...
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Old 6th February 2010, 02:14 AM   #16
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Alright, I've been thinking about this some more. I think the spark I saw where the power switch touches the metal plate it is mounted to ruined the switch as now I get no power anywhere in the amp. So, I think I need to add one more ground wire that grounds all the switches on the rear plate to the star ground. I'm guessing I also need to replace the power switch. Does anyone know a simple way to test if the switch is fried? Does it sound like I'm on the right track?

I'm guessing none of that has anything to do with my my reading of 0 or 1 at pin two of the 12AT7 so I'm still open to suggestions there.
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Old 6th February 2010, 04:06 AM   #17
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It looks like you have the switch mis-wired. When you threw it, it shorted the mains. With a typical switch, the center terminals are the common and the ends are the two poles. Toggle switches throw opposite of the handle. You have a DPST switch. In the pictiure, when you throw the switch, the white wire with the brown stripe is connected to the white wire with the red stripe. The white wire with the blue stripe is connected to the spade crimp terminal. BTW, if those are wires from an network cable, you need to replace them with something of a larger gauge wire.

The fuse should be the first thing from the power cord socket, then to the switch. You want the fuse on the hot side of the power socket. This is usually marked with an "H" or an "L". Also, you really should mount that fuse holder to something. The adhesive on electrical tape has a habit of "melting" off when heated. Tube amps run warm, so I would avoid using it and use heat shrink instead.

I am surprise those wires survived and I suspect that one of them is actually open or that you blew the filter inside the power socket.

Last edited by rknize; 6th February 2010 at 04:10 AM.
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Old 6th February 2010, 04:26 AM   #18
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Quote:
Originally Posted by bigjppop View Post
I can't find anything that looks like a short on the 12AT7 but maybe I'm blind. Seeing where the switches are mounted, do I need to ground that plate and the switches as well? As mentioned above, the RCA's and binding posts are both attached to the star ground.
The shorts usually happen on the top of the board, under the socket. The solder can sometimes blob on the other side if too much is applied.

Also, you definitely want to ground that plate.
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Old 6th February 2010, 07:00 AM   #19
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Quote:
Originally Posted by rknize View Post
It looks like you have the switch mis-wired. When you threw it, it shorted the mains. With a typical switch, the center terminals are the common and the ends are the two poles. Toggle switches throw opposite of the handle. You have a DPST switch. In the pictiure, when you throw the switch, the white wire with the brown stripe is connected to the white wire with the red stripe. The white wire with the blue stripe is connected to the spade crimp terminal. BTW, if those are wires from an network cable, you need to replace them with something of a larger gauge wire.

The fuse should be the first thing from the power cord socket, then to the switch. You want the fuse on the hot side of the power socket. This is usually marked with an "H" or an "L". Also, you really should mount that fuse holder to something. The adhesive on electrical tape has a habit of "melting" off when heated. Tube amps run warm, so I would avoid using it and use heat shrink instead.

I am surprise those wires survived and I suspect that one of them is actually open or that you blew the filter inside the power socket.
That definitely looks like at least one of my problems; I'll redo the wiring and beef it up while I'm at it. Is there anyway to tell if either the switch or the filter in the IEC are toast?

I'll also pull the board and see if I can find the short; the frustrating thing is that it worked on the breadboard, just not in the chassis!
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Old 6th February 2010, 11:54 AM   #20
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OK, I redid all the wiring (correctly this time) between the IEC and the switch with some 12 gauge wire, grounded the rear panel to the star ground, switched the fuse so that it sits between the IEC and the switch and still no juice running (I've been checking the 6.3V pins on the tubes).

After all that I switched to a new switch and still nothing. Is there anyway to test the toggle or the IEC socket itself to see if I wrecked them? I really don't want to place another order to Digikey if I can help it. I'm assuming everything on the board is okay because I can't see or smell anything wrong there and I'm also hoping that all the transformers are OK (a quick spark on first plug in shouldn't kill anything expensive, right?).

Any advice?
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