Power Help

[Telepathicicepop]

Hello all, first thread so bear with me...

I recently ordered/assembled this tube amp kit...

Found here

I followed the NEW wiring diagram to the letter and got everything good to go, put in the tubes, and hooked up a speaker load and flipped the power switch, and nothing happened. And by that i mean, no pilot light and the tubes did not start warming up. Also, after roughly 5 seconds, the Brown and Black wires from the Power transformer to a ground lug on the chassis started smoking/melting together so i quickly turned it off. I checked both the Mains and HT fuses, neither blown.

I went through and short checked everything in the power section and the only "Shorts" i could find were on the pilot light, (orange and black) and the impedance selector (all taps; to the output). I'm not sure if those are supposed to be shorted or not.

This is my first amp build and i'm not even sure where to begin.

There's an amp Tech about an hour away, but thats like a 3 week lead time and if its something simple why pay him way too much?

Hopefully i didn't just Coaster my Power trannie. Any and all help is greatly appreciated.

[Alex R]

There's an amp Tech about an hour away, but thats like a 3 week lead time and if its something simple why pay him way too much?

This may not be the best way to get help from a bunch of amp techs with a living to make on a forum.

[Telepathicicepop]

This may not be the best way to get help from a bunch of amp techs with a living to make on a forum.

Lol true, but i mean if the guy is 3 weeks deep with work, he's doing okay without my business... I definitely would have taken it there by now, if that wasn't the case

[Alex R]

I'd try to help you but I can't get your link to work.

[Alex R]

...oh hang on it just popped up...

[Alex R]

I guess those brown and black wires will be centre taps, one for the HT (red wires) and one for the heaters, which are wired via the pilot light. The pilot isn't meant to be shorted but will read a very low resistance to earth because the winding is low resistance and the centre tap is earthed.

There might be a short in the heaters wiring. As a first step you could try lifting those brown and black wires and seeing if you can still read a short on the pilot. If so, that's the fault and you have to find where the heater wiring (all those X-es) shorts.

[Telepathicicepop]

thanks much, i'll try that out and see how it goes.

like i said, hopefully my tranny isn't fried already

[Alex R]

There's a pretty good chance it's ok. But let's try some stuff with it turned off before we risk it.

[Alex R]

Oh pull all the tubes out too.

[Telepathicicepop]

so i removed the brown and black wires (attached to the chassis ground) only and the pilot light is no longer shorting to ground...

so does that meat the short is inside the transformer?

[Alex R]

No it doesn't at all mean the transformer is bad.

So the short isn' t in your heater circuit, which leads us to the HT circuit - red wires. Can you just check you have the rectifier diodes all wired in the right way around? And your polarities are right on the big can caps?

After that we'll probably need a light bulb limiter - easy to build if you don't have one already. That lets you run an amp with the short in it without burning anything up.

[Wilder Amplification]

Here's a link to the spec sheet for that transformer -

http://www.classictone.net/40-18023.pdf

Sounds like you grounded the wrong black wire, which essentially shorted out 1/2 the heater winding. There are TWO black wires on that PT secondary...one of them is the HT center tap while the other is one side of the heater winding. Ground out the wrong one and you short 1/2 the heater winding out. So...swap the two black wires.

[Telepathicicepop]

Thanks VERY much, i'll try swapping the wires after work.

And yes, all of the polarities are correct assuming the parts are labeled correctly.


you dudes rule!

[nickb]

Also, you might want to check the fuse rating & type. Consider changing to a faster acting and or lower current rating. My feeling is that it should have blown under these circumsatnces.

Use the light bulb feed before you do any more.

[Wilder Amplification]

Also, you might want to check the fuse rating & type. Consider changing to a faster acting and or lower current rating. My feeling is that it should have blown under these circumsatnces.

Use the light bulb feed before you do any more.

One would think, but because it is a step down winding to low voltage/high current, an 8 amp draw on the heater winding would only cause a 420mA draw on the mains winding, which means that the "short current" on the heater winding may not have translated to enough mains current to blow the mains fuse in time (it takes a much larger current increase on the heater secondary to cause enough of a mains current increase to exceed the current rating of the mains fuse).