Metropoulos Forum

Hola. I'm new to this and as such upon flicking the switches to ON after completing my first 2204 clone build, I got a little bit of smoke and noticed the ground wires from my power transformer started to sag. They were humming and heating up quick fast. I ended up having to wrap them in some electrical tape because they actually managed to melt through in a couple spots. The layout I am following is this one...

http://www.joepopp.net/jcmtwins/jcmtwins003big.jpg" onclick="window.open(this.href);return false;

So the wires that are going nuclear on me are #7 and #10 on the PT. I tried disconnecting 8/6 from the turret board as well as 11/9 and tried powering things and then taking a reading with my voltmeter. The following is what I got...

http://frankblo.ws/DSCF4015.AVI" onclick="window.open(this.href);return false;

Similar results happened for the other set that didn't get tested in that video. The transformers I am using were bought from Triode. This is a 50W PT. Does anyone have any insight as to what I could have possibly done wrong? The only difference from the schematic I am using and the power transformer I have is that 8/6 would be 345V instead of 323, as that part of the transformer is rated @ 690V. 11/9 are fine as those on the transformer are rated 6.3V like the diagram.

At the suggestion of a more electronically inclined amigo, I went ahead and checked all of the resistors on the turret board. All of them read their normal readings except for the one identified in the following modified diagram...

http://frankblo.ws/low.jpg" onclick="window.open(this.href);return false;

When I took it off the turret board it read as 100K no sweat, but when installed on the turret board it reads ~4.5K. This drew my eye to the 4.7K resistor between the bus bar and ground on the presence pot, but I don't see how this could be related. Then again, like I said, I am new at this.

Any and all comments would be greatly appreciated. I really wanna fire this thing up!

Pictures of your wiring would help . Is is possible you have the cap can wired wrong where the center tap attaches? Make sure it's on the ground of the cap can.

My cap can wiring is fine. I followed this schematic exactly and ensured after every connection that I was checking and double checking to ensure I was hooking things up correctly. I will get some pictures of the wiring coming off of the power transformer as soon as possible.

haskell wrote:My cap can wiring is fine. I followed this schematic exactly and ensured after every connection that I was checking and double checking to ensure I was hooking things up correctly. I will get some pictures of the wiring coming off of the power transformer as soon as possible.

Definitely post pictures. Sounds like either something is shorted somewhere or maybe your bias supply isn't working correctly. Did you make sure to ground the bias supply?

Check your voltage at pin 5 on one of the power tubes with the amp on in "standby" mode (shouldn't see any smoke in Standby mode since the high voltage is off) and make sure there is a negative voltage there. Without the negative voltage, the power tubes will essentially perform like a short circuit and pull way too much current.

I think the PT I have is toast. I'm assuming there should be continuity between (referring to the joepopp.net schematic above) pairs 6 & 7, 8 & 7 and 9 & 10, 11 & 10. There isn't. I have it between 11 & 10, and that's it. I checked with an electronics buddy of mine, but I wanted to be for sure for sure and check here in my post. He supposes that I shorted something somewhere along the way resulting in my toasting of the transformer. Any takers? Am I ordering a new PT?

The only way to know for sure is to completely disconnect the secondary side of the transformer from the amplifier, then turn it on and see if it blows the mains fuse or if you see smoke. If it does, then it's definitely bad.

If it doesn't, this doesn't mean that it's still good. Measure your AC voltages on the different taps and verify that they're all right about what they're supposed to be. Chances are if the voltages are correct then the PT is fine.

Set your meter to measure resistance, then check each wire on the PT and verify that none of them are shorted to the transfomer core.

However, if the PT is in fact bad, you'll want to find out what shorted downstream of the PT that fried it.

I disconnected everything and checked the voltages, they are far from fine, so I'm 100% certain I'm in the market for a new transformer. So I guess while I wait to place and order and have it shipped, I'll have plenty of time to check out where the short is.

Thanks to all who posted!