Rectifier help

[sixstringer]

I have a Hammond 269EX going to two N4001 diodes to form a bridge rectifier. The center tap of the B+ is going to ground. I have 205vac per side into the diodes but only 245vdc coming out. I could change the rectifier to full bridge, adding two more diodes, lift the center tap ground from the transformer and ground the rectifier, would that work better? I think I should be seeing around 300vdc from the rectifier. What am I missing?
Thanks for your advice

[martin manning]

1N4001 is not rated for the voltage you are applying. Use 1N4007.

380V CT means 190V on each side, so you should get 190*1.414=269V peak, and about that in DC, and you need a capacitor to realize it. The diodes need to handle 2x that voltage or 538V... 1N4001 is rated at 50V.

[sixstringer]

Thanks, I don't understand why but moving the ground from the center tap of the transformer to the negative side of the rectifier fixed the issue. i now have 379 vdc out of the rectifier. I was mistaken about the diodes, they are N40007 rather than 40001. Ultimately, I'm trying to find out why this amp sounds so lifeless, I was expecting the usual chime that I've gotten with other EL-84 based amps I've built. After chasing around the tone shaping component values in the circuit, I decided to check voltages and discovered how low they were. Maybe this jump in vdc will improve things.

[martin manning]

That's not making sense to me. See: http://www.hammondmfg.com/pdf/5c007.pdf You should be connected as shown for full-wave capacitor input load.

[wpaulvogel]

Something is wrong. Use one diode per red wire, ground the center tap. This is full wave rectified. You must have a capacitor. Positive connected to the diodes and negative connected to the center tap. Key!! Connect the ground lug of your power cable to the ground of the center tap/capacitor!!
The transformer should make really close to 300 volts unloaded.
If you choose full wave bridge, your voltage DC is going to be really high
410AC x 1.35 = 550+ volts DC. BAD

[sixstringer]

this is how it's wired now. This is from Mat's 86 Special layout from a few years ago. I added an additional EL84 in series to make it dual single-ended.

[martin manning]

Hammond 269EX is intended to be wired using a FW rectifier. If you connect it to a FWB (ignoring the CT), the voltage will be too high (~600V unloaded) and the secondary current capability will be reduced by half.

Connect the ground lug of your power cable to the ground of the center tap/capacitor!!

These grounds should be separate. Connect the reservoir capacitor ground directly to the PT CT, wherever it is grounded, but give the power cable earth ground its own dedicated chassis bolt.

[sixstringer]

Posted in error

[sixstringer]

Here is the schematic

[martin manning]

This looks better.

[wpaulvogel]

I had no idea it was rigged up in an amp. I thought you were testing on a breadboard or something. Single ended EL84 amp should work pretty good at that voltage. 250 on the plates and screens should be nice.
Class AB push pull needs 300 volts maybe a little more but class A single ended is going to be pushed at 300 volts.

[sixstringer]

Martin, that's how I had it originally, which made more sense to me but I was only getting 245vdc B+ and the amp had no punch at all, after changing to it, the vdc went up over 100vdc and it sounds much better, but I'm thinking of adding a diode to lower the B+ a bit. I still like your circuit better by the vdc is too low, I don't understand why.
Thanks for your time and advice.

[PaulD]

this is how it's wired now. This is from Mat's 86 Special layout from a few years ago. I added an additional EL84 in series to make it dual single-ended.

I assume you mean an additional EL84 in parallel? In any case this is the cause of the low voltage, your transformer is only rated for 71 mA and 2 x EL84's will be trying to pull more than that causing the voltage drop.

[martin manning]

Good point! A larger PT is needed.

[sixstringer]

Even if i have only one El-84 installed?