Negative voltage for el34

[fossilshark]

 i built the negative bias voltage circuit and im reading 54v ac in and -12v out. What circuit should i be using to get -54v from 54v ac? Or do i need a higher voltage to start with.

[sluckey]

Something is not right if -12v is all you can get from that circuit. Disconnect the supply from the load to see if the problem is with the bias supply or the load.

Show us the rest of the circuit.

[PRR]

Yes, what load is connected?

Is the cap in, and good? Simming a super-small cap I get 18V mean value, but some meters may mis-read this very ugly wave.

Re-re-check resistor values. I can't get 12V with the usual factor of 10 errors (120K instead of 12K etc), but both values are important.

However: I do not get -56V DC for 56V AC from these values. I get 36V. You should be able to get this to prove the basic build is correct. To get 54V DC from 54V AC, I figure the "12K" should be near 3.5K.

[fossilshark]

I had no load connected when i measured these. There was -30v right off the diode before the resistor. Ill try switching out the 12k, do these resistors need to be high wattage?

[HotBluePlates]

No, 1/2w is plenty.

[fossilshark]

If i put a 10k pot where the 12k is, whould i get an adjustable boas voltage?

[PRR]

Show us the rest of the circuit.

Is the cap in, and good?

[sluckey]

I suspect the cap is bad or installed backwards.

[fossilshark]

Just bought the cap and i triple checked the polarity, Im suspecting the diode because its massive, and was only marked "1000v 1A" when I bought it off amazon. i just recieved the 1n4007s im using for the rectifier so ill try one of those. i drew these schematics using a laney supergroup 69' as a reference except the power amp is from the stock JCM800 2204.

[PRR]

That plan needs a 78V AC winding to make 54V DC.

What do you really need? What do you have?

[fossilshark]

The bias tap on the PT is reading 53v (+-1v) and i need the -54v. What about a voltage doubler circuit?

[Ambugaton]

Do you just have your probes reversed? I mean... Occam's razor

[PRR]

> What about a voltage doubler

No, you just need right-size resistors. I also note the ripple is poor. Do it this way:

[fossilshark]

that helps alot, i blew my last fuse (shorted something but its fixed now) so when i get more i will put that in. Thanks