My new general question thread. (Renamed rectifiers and bl..

[tribi9]

Can a bad rectifier tube cause the fuse to blow on an amp? As soon as I plug in my amp, not even switched on, just plugged in the fuse blows.

Thx for your help guys.

Ronald

[Phil_S]

Think about this a minute and you can solve the problem.

If you plug it in and the fuse blows, then there is a short somewhere between the mains line feed and the fuse. There isn't much to look at. Mains feed, fuse, ????. You may have an unintentional ground.

Your circuit should look like this:
mains+ > fuse > switch > PT primary
mains neutral > PT primary
mains ground > amp chassis

You plug it in and the fuse blows? The switch is not breaking the circuit and something is drawing a load of current (amps).

The rectififier does nothing until you close the power switch. Maybe you miswired the switch and it doesn't matter what position it's in?

[tribi9]

The amp was working fine before. I re wired the heaters with slightly thicker wire that's all I did. I do have have the white end of the cord going to the fuse and black going to the switch tho'

What is the standard for cords?

White Live
Black Neutral
Green Ground?

Cuz If it is then I have the live and neutral reversed.

[M Fowler]

White - neutral
Black - main
Green - ground

I am still questioning information from your other post about the wiring of the filament string though?

[tribi9]

I am still questioning information from your other post about the wiring of the filament string though?

The 6.3 wires coming out of the lightbuld go to Pins 2 and 7 on the 6V6 then one of the wires goes to pin 4 and 5 and the other to pin 9 on the 12AX7. Actually when I rewired I think from the t

The way I have it wired now is

white>switch>PT primary
Black>fuse>PT primary
Green>ground

And like I said before it worked fine before I rewired the heaters. What I did notice tho is there were some wire strands that shorted the two 6.3 heater wires coming out of the PT if that makes any sense.

[Structo]

That'll do it.

[tribi9]

That'll do it.

Yeah, when I soldered them to the back of the lightbulb one of the wires had some strands that were long enough to make contact with the other wire.

So I guess I did have the AC cord right then.

[Phil_S]

The way I have it wired now is
white>switch>PT primary
Black>fuse>PT primary
Green>ground

For starters, put the switch on the hot leg:
black>fuse>switch>PT
This will let you plug it in without blowing the fuse unless the problem is between the wall and the swich.

Then, look for a whisker or other unintended ground. Use a magnifying glass if you need to. Check the circuit for continuity beyond the switch (with the switch off/open).

[tribi9]

Phil,
So the White (neutral) just wired straight to the PT wire? See the schematic shows one wire going to the fuse and one wire going to the switch. That's why I'm confused. It doesnt show a wire going to the fuse and then the switch.

I know it should be a really easy concept but to me it would make more sense if it were like this....

Live wire goes to the switch then PT. Then the neutral to to the fuse and then PT. Green to ground.

[ampdoc1]

Here is a diagram

[tribi9]

Thx guys.

[tribi9]

So I rewired the AC cord according to the diagram and the amp is working again. One thing I want to mention is as soon as I started it the first time I noticed the amp was louder than before but the treble, bass, and speed and intensity for the Vibrato were not working. I opened it up and noticed two grounds had come undone. One from the bass pot and the other one for the intensity pot. I resoldered the grounds and the treble, bass, intensity and speed all started working again but I did noticed a drop in volume.

So my question is since I really like how it sounded and how loud it was before I grounded back the two pots. Could anything bad happen if I remove the ground for the vibrato and just leave it like that? I don't care much for the vibrato if the difference in sound is that huge.

[morcey2]

So I rewired the AC cord according to the diagram and the amp is working again. One thing I want to mention is as soon as I started it the first time I noticed the amp was louder than before but the treble, bass, and speed and intensity for the Vibrato were not working. I opened it up and noticed two grounds had come undone. One from the bass pot and the other one for the intensity pot. I resoldered the grounds and the treble, bass, intensity and speed all started working again but I did noticed a drop in volume.

So my question is since I really like how it sounded and how loud it was before I grounded back the two pots. Could anything bad happen if I remove the ground for the vibrato and just leave it like that? I don't care much for the vibrato if the difference in sound is that huge.

The vibrato shouldn't make any difference in volume when it's off. The boost you were hearing was from the tonestack being bypassed. I've built quite a few amps w/ tone-stack lift switches on them and you get a real nice boost from it. It won't hurt anything as long as the following stage still has a good ground reference. An easy way to do is is to put a 470k resistor across the switch. With it turned on, it's just like a normal tone stack. With it off, it's like having a 500k mid pot turned up all the way. That is all assuming it's a standard TMB stack (or TB with a mid resistor is what it sounds like in your case). If it's a James/Baxandall stack, the same thing can be done, but someone else'll have to direct you on that one.

Matt

[tribi9]

Ok, but out of the treble and bass pots only one is grounded so how would I go about making sure the "next stage has a good ground reference"

What would be the proper way to remove the treble and bass from the circuit?

[morcey2]

Ok, but out of the treble and bass pots only one is grounded so how would I go about making sure the "next stage has a good ground reference"

What would be the proper way to remove the treble and bass from the circuit?

That depends. What type of amp is it; or do you have a schematic for it?