Fuse is blowing instantly (SSE)

[Divad89]

Just connected the whole SSE on a test bench, but as soon as I power it up the fuse is blowing, while there is some kind of buzz.

I've made a complete wiring diagram of my connections, because of the different color codes than tubelab's:

An externally hosted image should be here but it was not working when we last tested it.

OPT's: Edcor CXSE 25-4-5K:

http://www.edcorusa.com/Images/Products/SCM/CXSE-4.png

PT: Edcor XPWR059:

http://www.edcorusa.com/Images/Products/SCM/XPWR059.png

Choke: Hammond 193H

Because I don't have a grounded receptacle, I've put a metalspear outside in the ground, and connected ground to that.
Before I powered up the amp, I followed Ty's Simple SE checkout guide, and measured all the resistors.

---
David

 

[Ty_Bower]

Just connected the whole SSE on a test bench, but as soon as I power it up the fuse is blowing, while there is some kind of buzz.

If the fuse blows instantly, you've got a short to ground somewhere.

Are you using a vacuum tube rectifier, or solid state? Did you choose the optional choke and/or motor run capacitor?

Refer to the Simple SE schematic, and with the amp off and power disconnected check the DC resistance between ground and the various points leading from the power supply (+ side of C1, + side of C2, pin 3 of the output tube sockets). You should see no less than 150K ohms to ground at any of these points.

 

[Divad89]

I've both vacuum tube rectifier and solid state, but do I need to put the rectifier switch on when there isn't any tubes in it yet?
I have connected the choke (193H), and have a motor run cap, but haven't connected it yet.

I've just tried to measure all the points you specified, and all of them showed just about 75K ohms after a while.

---
David

 

[Ty_Bower]

I'd keep the motor run cap out of the circuit until you've got things figured out.

With no choke installed, you need the 150 ohm R1 installed. Of course, once you put the choke in you must take R1 out.

You are correct on your 75K ohm measurement. I forgot that R2 and R4 are in parallel.

Do you have SW1 installed? Is it open, or closed? The solid state rectifiers are a common cause of problems, especially if they are not the Fairchild parts. They tend to fail short circuit, which results in blown fuses. If they fail shorted, they WILL blow the fuse regards of whether SW1 is opened or closed.

 

[jrn77478]

If they fail shorted, they WILL blow the fuse regards of whether SW1 is opened or closed.

That's a likely suspect. Next, or maybe even higher on the list, check your wire connections carefully, with good light and some magnification. Sometimes that stray whisker is pretty hard to see.

 

[Divad89]

Should I take the solid state rectifier out, mount the rectifier tube and close the SW1 then?

---
David

 

[urmoo]

Check out wires of power transformer. I got EDCOR PT with mixed wires- colour in schematics didnt match with device and fuse kept blowing... in my case black/w was mixed with green/w

 

[Divad89]

So I can't be sure of the color codes on the schematics they have sent with the transformers? How can I know which are the right ones?

---
David

 

[Ty_Bower]

So I can't be sure of the color codes on the schematics they have sent with the transformers?

The color codes indicated on the sheet of paper that shipped with the transformer are correct. They just might not necessarily match the colors shown in the Tubelab diagrams. For example, sometimes Edcor will use something weird like brown for the 6.3 volt, or green for the 5.0 volt.

The important things to check are that the 6.3 volt winding is connected to the T1-GRN terminals, the 5.0 volt winding is connected to the T1-YEL terminals, and the high voltage winding is connected to the T1-RED terminals. You also need to have the high voltage center tap connected to either of the T1-RED-YEL terminals (doesn't matter which one, and just leave the other one empty).

Which solid state rectifier diodes did you buy, the IXYS or the Fairchild? If they are the IXYS, I'd probably take them out. You don't need to do anything with SW1 - don't wire a switch to the board, don't put a jumper across the terminals.

If you take the two solid state rectifier diodes out, you should be able to complete the voltage checkout of the board. Of course, you'll need a vacuum tube rectifier (probably 5AR4) when it comes times to actually make the thing sing.

 

[Divad89]

That did the trick, took out the solid state rectifier... but I think the PT is buzzing pretty much?

---
David

 

[Ty_Bower]

...but I think the PT is buzzing pretty much?

It depends how much. Most nearly every PT of mine makes some degree of mechanical noise. It may change depending on whether or not you've got a load on the supply. Can you quantify how loud it is? Are we talking a hum like some piece of machinery in the far off distance? Or does it sound like a pair of hair clippers that isn't adjusted properly?

Most of the Edcor transformers are pretty well varnished, so it shouldn't be too loud. I've got an Edcor PT, and it makes a fairly quiet buzz.

 

[Evenharmonics]

the PT is buzzing pretty much?

Buzzing seems common for that type of PT. Hammond brand is known for that. I switched to toroidal PT for my TSE (not SSE) and it solved the problem.

There is a thread on buzzing PT for TSE which Tubelab himself posted about his experience with buzzing PT after the old power line transformer outside (struck by lightening) was replaced with new one.

 

[Ty_Bower]

I switched to toroidal PT... and it solved the problem.

I've got a toroid PT in an AudioSource Amp Three, and it sometimes buzzes too.

 

[urmoo]

The color codes indicated on the sheet of paper that shipped with the transformer are correct.

Nope, In my case the color codes on the paper did not match with wires of transformer.

 

[Evenharmonics]

I've got a toroid PT in an AudioSource Amp Three, and it sometimes buzzes too.

I use one of those amps for my home theater setup but haven't heard it buzz at all. When yours does sometimes, could that be from fluctuating voltage at the wall outlet?