Problem with new Vibroverb clone

[Marcfrom]

Hi guys,

I just finish a Vibroverb clone, but i have a problem with the rectifier.

Actually when i take off the rectifier, it seems ok, i can find 368 VAC on the red (pin 2 and wires and 5VAC between the two yellow (pin 2 and 8)wire(pin 2 and .

When i put the rectifier tube i can find the 368 VAC, but the 5 VAC between the two yellow wire diseapper, i see 0VAC and there is no B+ DC voltage.

Of course there is no light in the tube.

I tried with another rectifier tube, but it still the same, i don't understand.

Does anyone have an idea ?

Marc

[Phil_S]

Using a GZ34/5AR4? Take the B+ from pin 8, not pin 2. Pin 8 is the cathode. Pin 2 is only the filament. You are loading up the filament supply with the whole circuit and it is dying under the load.

[rogb]

Yep, pins 4 and 6 take your HV AC in from the PT, yellows 5v AC to 2 and 8, and B+ from 8 to your PS board.

Just did an AB763 and it works fine

[Marcfrom]

Yes it's a GZ34, i already take the B+ from pin 8.

But when the rectifier is in place there is no 5 VAC between pin 2 and 8. i find tis 5V when i remove the rectifier. I tried to disconnect the B+ and it's the same

I just tested this rectifier in another amp, it's work properly.

So ????

[Phil_S]

Try reversing the 5V wires for pins 2 and 8. Maybe there is a weird phase problem?

[Marcfrom]

Ok, i tried it, it's the same.

I keep only the 5V yellow wires and when i plug the rectifier there is no voltage.

How it's possible? Is it possible this problem come from the transformer ?

[img:640:853]http://nsm07.casimages.com/img/2012/02/18//1202180150111310609453588.jpg[/img]


[img:640:853]http://nsm07.casimages.com/img/2012/02/18//1202180150291310609453589.jpg[/img]

[greekie]

Does the tube work in your other amp? That could be a short.

[Marcfrom]

yes the rectifier tube work in the other amp.

You talking about a short in the transformer ?

[Phil_S]

The tube works in another amp, so it's not the tube. The PT puts out 5V, so it's not the PT. I think that leaves the socket. Try another socket? This is weird.

Are you sure the PT has 5V @ 1.9A available? If it only has 1A available, that isn't going to power the rectifier.

The only other thing I can think of is the wires. Show us a picture of the socket seated in the chassis and wired up. Maybe we will see something you are overlooking.

BTW, that's a nice trick, holding two probes and taking a picture all at once? How'd you do that?

[Marcfrom]

The transformer come from the Mojotone kit, so normally it must fit with the kit, i checked the ref it's the good one.

I thinked about the socket but i don't have more, so i will solder the wires directly on the pins.

I'll post some pics of the socket after the test.

For this pics, i just used my third hand

[Phil_S]

Before you solder directly to the tube, just check all the socket pins for continuity to each other. Obviously, there shouldn't be any between pins. Also check that continuity exists from the top to the bottom on each pin. If you find nothing out of the ordinary, maybe you can swap with one of the other octal sockets.

[Marcfrom]

I done many test today.

I disconnected all secondary and only keep connected the center tap 0V ( red yellow), and the yellow wires on a pilot lite bulb.
I also unscrew the transformer from the chassis.

So, this bulb doesn't blow, i can see a very, very small light on the filament. I measure 0VAC between the two yellow wire when it's charged by the bulb.

I'm now sure the problem is caused by the transformer and the 5V secondary doesn't work.

I hope Mojotone will send to me another one without problems!!

[img:640:853]http://nsm07.casimages.com/img/2012/02/19//1202190259001310609458943.jpg[/img]

[Phil_S]

You should check it with all wires fully disconnected. This includes the CT and the pilot.

Set you meter for Ohms and then check to see you don't have continuity across windings. When you find, for example, that the 5V and HT secondaries are cross connected internally, then you can be sure that it isn't right. If you find nothing like that, then power it and check all the voltages, including each outer leg of the HT secondary to the CT. Nothing should be grounded.

[Marcfrom]

I sent back the transformer to Mojo and waiting for a new one.