Ceriatone SOY bias supply?

[PlinytheWelder]

I'm building one of these, just about done. Brought it up on a Variac and light bulb limiter and I don't seem to be getting bias voltage.
Here's the layout, no schematic available yet.

[img994]http://ceriatone.com/images/layoutPic/H ... Layout.jpg[/img]

Maybe I don't get it, but I don't see how the bias supply can work as laid out? In fact the whole supply section looks a bit weird to me... Any insights?

[martin manning]

Looks like a yellow bias wire from the PT is shown going to both ground and the 1k5 resistor on the board. Obviously it should not be grounded. Run the bias tap lead from the PT to the 1k5 on the board and you should be okay.

[roberto]

Well, it has to go to ground.
It's a single winding dedicated to bias.

One end to ground, one end to the bias circuit:
15 kOhm - reversed diode - cap - 10k pot and 15k to ground.
That's ok.

Check ac and dc voltages on every stage of the bias circuit.

[PlinytheWelder]

That's the weird thing, I ve seen pictures of this amp with that wire grounded...And supposedly it works... I don't see how...

Here's some gutshots of one on ebay... Sure looks grounded to me
[img768]http://i1154.photobucket.com/albums/p52 ... pwukfd.jpg[/img]

[img768]http://i1154.photobucket.com/albums/p52 ... t7fury.jpg[/img]

[img768]http://i1154.photobucket.com/albums/p52 ... hjnyon.jpg[/img]

In fact both sides of the bias supply look grounded to me...

FWIW, I'm not using Ceriatone transformers. I'm using Classic Tone in mine.There is no bias winding. Another weird thing is that the B+ center tap is kept floating on the main supply and not connected to ground. Unlike a Marshall

I wish I had a schematic. I'm used to looking at circuits like that. Worst come to worst... I'll just make up a turret board and make my own supply.

[PlinytheWelder]

Ok.... now I get it... Both yellow wires are the bias winding... Duh! I just don't have them on my tranny. I guess I'll have to make my own bias board and do my own supply. A handful of components ought to do it.

[roberto]

Post the specs of your trafo.

[martin manning]

Roberto is right, it's a separate bias winding with both leads being yellow. If you have no bias winding you'll need to do a capacitive coupling to the HT.

[roberto]

Check your PT to understand how it works.
Maybe you can switch from 15 kOhm to 220 kOhm and use a HV tap.

[martin manning]

Check your PT to understand how it works.
Maybe you can switch from 15 kOhm to 220 kOhm and use a HV tap.

Can't do this with a FWB rectifier.

[PlinytheWelder]

I'm using this tranny... http://www.classictone.net/40-18056.pdf

[PlinytheWelder]

If I have to, I can make up an Express type supply and drop it in there. Either just the bias or the B+ and the bias...

[martin manning]

Hold on there, 580V CT into a FWB is going to give 800V! If you are going to use that PT you'll need to set it up as a FW, which you can do on the PCB. Then you can tap the bias off of the HT, and just increase the value of the 1k5 at the input to 150k or so.

[PlinytheWelder]

Yeah.... that looks like what I'll have to do... I can take 2 of the bridge diodes out and use the center tap. Then scale the bias resistors appropriately...

I just simulated the supply in the Duncan PS program and got 700+ Volts. No wonder I was getting wacky high B+ when I brought it up to like 60V on the variac.

[M Fowler]

I know your using a different PT but this is for those using Ceriatone supplied PT and OT. I previously posted this on your other thread.

Primary Side:
Red 240V
Blue 120V
Orange 100V
Black 0v
Secondary Side:
Purple HT
Gray HT (smaller gauge wire)
Yellow bias
Yellow 0v ground to chassis
White 6V (for relays not used)
White 0v (for relays not used)
Brown 6.3v
Gray CT (larger gauge wire)
Brown 6.3v

http://ampgarage.com/forum/download/file.php?id=41502