V4 ONLY works on my bench

[DrGonz78]

When you note "Bench and Regular Power" is that in the same building? Or is regular power just an example of separate measurements at your house or some other location? I would be testing as many outlets in that building as possible.

[nsubulysses]

Regular power is recording studio power. They have run 1000 amps for like 8 years without weird phenomena.

I work in a warehouse that is over 100 years old. It is divided by a brick wall into two sections. My "work space" is on the side that has a recording studio, storage area, and office area. The other side is a woodshop. I use the woodshop power via extension cord so i have my own power because the studio wished to have its own breaker to itself. I'm right next to the studio. I didn't run the extension cord, it has been there for years or decades and just so happened to conveniently be right next to my bench when I figured out where I wanted to set it up.

I will have to check outlets in the office and other parts of the building and move to a properly grounded one. Thanks for helping me sort why my bench is special, everyone. Nothing strange like this happened for about 40 amps. Then this V4 came along.......

[J M Fahey]

Friend, fix that NOW !!!!!
We'd hate to lose you.

So far you've just been lucky.
Amps "worked" because they got 121V between hot and neutral and that's all they care about, but had any of them had a gross mains side short, maybe a burnt PT which becomes a shorted block of toasted metal and you'd be accessing the Forum through a Medium.

Hire a certified electrician (no kidding) to run proper power to your bench.
They have, besides the licence, experience on all sorts of odd old buildings and have seen it all.

That said, that amp still has one gross problem, it just does not show up on your bench , for reasons we now understand.

[TimmyP1955]

And take the death cap out of that amp.

[nsubulysses]

Death cap will be removed. Strangely I got 3 blackface fenders from a guy who had them all of them worked on by the same tech before he moved. 2 of the 3 had death cap removed but not this one.

I know you all couldn't make it to the opening ceremony of my new bench AC supply so I took a pic !


This V lights the lamp when I flip the standby switch on, even when the on/off switch is off. I'll have to get back into this thing another day. At least one thing is solved though. Thanks! There was a break in continuity in the ground in the extension cord. Woodshop power is ok.

[g1]

This V lights the lamp when I flip the standby switch on, even when the on/off switch is off.

Either the power switch has welded itself closed, or you have something miswired at the power switch or shorted death cap.

[nsubulysses]

I have continuity between the blue/blue and white winding of the PT and the high voltage secondary. There is not continuity between black/black and white primary and high voltage secondary.

How is it possible the amp worked on my bench before I fixed the power if the primary is shorted to the secondary, or am I missing something? This was tested with all PT leads disconnected.

[Enzo]

Is it still wired into the circuit? Disconnect the transformer wires then verify the short between windings really exists, and is not really a short between the circuits in the amp.

[g1]

With all PT leads disconnected then, you have a short from primary to secondary of the PT. It's shot. Somehow with your missing earth ground at your bench outlet, it was able to work. Just another reason why safety earth ground is so important. As you know, with any properly grounded outlet, the fuse blew instantly.
But you probably want to know how it worked without the properly earthed chassis . I'll leave that to anyone who is less sleepy than I am right now.
The other clue being that the limiter lamp lit when standby was thrown, even with power switch off.

[nsubulysses]

Now it makes sense. There is sound through the speaker with power on and standby off because there is high voltage on the secondary side due to the short.
This also explains why sometimes after the fuse would blow, the standby light would stay lit, only turning off when the amp was unplugged.

I searched for hours for an error in my power supply recap or some sort of intermittent short. How bizarre.

Now that all the fun is over, let's go further. When I got the amp back two separate times after the fuse blew i noticed the tone knobs were in extreme settings. Mids and treble cranked, sensitivity and eq rocker switches cranked too. I came to find that with these settings, once the volume gets past 3 the amp oscillates. if you change the mid frequency rocker switch it changes the frequency of oscillation. I thought the customer was blowing the fuse because the tone settings were sending the amp into oscillation at turn on, before power supply caps were charged up. This was about the 4th time I "solved" it.

I had a handful of V-series amps in my workspace so I started testing a few different ones. The two in the video are regular V4s that work fine, not the one from this thread! They all squeal exactly the same. Has anyone else ever noticed this or had a problem because of this?
https://www.youtube.com/watch?v=sLZd...ature=youtu.be

[J M Fahey]

But you probably want to know how it worked without the properly earthed chassis . I'll leave that to anyone who is less sleepy than I am right now.

No big deal and has already been mentioned: the transformer still received 121VAC (as measured and posted by Guitician) between hot and neutral, and that's all the primary cares about (that it's unsafe is a human problem) and either the hot wire or some point of the primary winding different from neutral is shorted to secondary or laminations (what I suspect) which *would* short that voltage to ground ... IF ground existed, which on the bench did not; now on any proper wired outlet that gross short blew the mains fuse ... as it should.

I imagine that rather than the hot wire shorted to chassis ground (remember neutral is actually floating, and usually lives a few volts away from real Planet Earth ground) some winding wire with not much voltage difference, maybe less than 20VAC , has insulation burnt or scratched and touching laminations ... which are bolted to chassis.
Such low voltage can pass undetected by human hands , or at worst very slightly tickle ... but when properly grounded it becomes worse than a shorted turn: *many* shorted turns and blows the fuse.

Maybe it's not so, but is an explanation which to me matches most known facts so far.

Of course that transformer is shot and a death trap, both electrically (just plug the amp into a reverse wired socket with no ground, perfectly possible, specially at a Club and the amp now can kill the user) or thermally: the short will overheat the transformer and if users use a large fuse, it will not blow but the transformer will overheat and possibly catch fire ... even if power is turned off.
Talk about a ticking bomb !!!!!!