Blowin fuses

[Mike]

hey all, fired up my A1a build and it blows fuses right away. No tubes in it. I just wanted to check voltages.
Any ideas??

Thanks
Mike

[Elcabong]

There is not much I can recommend besides to check and recheck your wiring! Without tubes in it, the load is the PS capacitors charging and then the current should stabilize.

Does the fuse blow with the standby switch open or when you close it?

I recommend that you read Paul Ruby start up procedure http://paulrubyamps.com/info.html#FirstPowerUp if you have not done so yet.

[Elcabong]

... and if you plan to build more than one amp, it may be usefull to build this widget. Go to http://www.geofex.com/ and scroll down to the Soft Power On Tester for Amplifiers link. It acts like a variac and will save you many fuses.

[Mike]

are all the jacks supposed to be insulated from the chassis or plastic??

Mike

[Elcabong]

are all the jacks supposed to be insulated from the chassis or plastic??

It depends on the grounding scheme you are using: buss or star ground? A mix of both or none?

This can affect the noise level in your amp but would not blow fuses. Also notice that the output jack(s) need to be grounded for the feedback loop to work.

Any progress in troubleshooting your problem?

[Mike]

Well, had a backwards filter cap and after I turned that around the tubes light up but no sound.
I am not getting any readings from the tubes except for 3.2 on the pins that are connected to the trannies.

With the Hammond PT am I supposed to ground the center tap for the rectifier diodes??
What about the input?? I have coax connected to the input and then to V1 but I don't have the second wire( the wire that wraps around the main wire) connected to anything. It shows on the schemo that it should hit a 100K R. Does anyone do that??
Anything else I should look for or know about??

Thanks a lot for the help~!!
Mike

[Elcabong]

With the Hammond PT am I supposed to ground the center tap for the rectifier diodes??
What about the input?? I have coax connected to the input and then to V1 but I don't have the second wire( the wire that wraps around the main wire) connected to anything. It shows on the schemo that it should hit a 100K R. Does anyone do that??

If the center tap is not grounded, the circuit is open and no current can flow from the PT secondary. So yes it needs to be grounded.

The coax shield is usually grounded on one end only. I just noticed that it is connected to the plate in some schematics; I guess it works but I would not be able to explain the advantages. If you do it this way, be sure to put some shrink tube on the other end as it is at high DC potential.