Pultec clone - grounding problems

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morls

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I'm not sure I see an issue unless the physical size is prohibitive.
There's room beside the main board for the caps.

On the layout, what's on the new heater pcb - rectifiers, reservoir cap, and filters? ie. everything for the DC heaters?
Yep.

The one loop you should keep small is the heater AC wiring, diodes, and first reservoir cap so, your option two sounds like it'll do that.
Still twist the wires from the DC output end of your new pcb and route them back to the heater input of your main pcb.
Thanks.
 

Nbtone

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I tried to order the caps for the power supply I designed in PSUD. That’s way too much to do for a heater supply. I’m going to try some low noise resistors to see if the hiss goes away. I called the supplier for the grounding devices that were sent to me, and he said I should tack them to each of the three wires coming from the wall socket. When I get some time I’ll try it.
 

morls

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I managed to get the rectifier and filter circuit into KiCad and model it, and output the gerber files. The cost of a couple of boards is $150, so I thought I'd do a P2P type build to make sure it's going to work. I haven't finished all the connections yet, but does this look ok so far?


P2P Rectifier 1.jpg P2P Rectifier 2.jpg


Just need to confirm this before I install and test:
Don't forget to remove the 6V winding's centre tap from ground.

Once you have your rectified and filtered clean DC, grounding the negative of that supply should be OK without elevating it.

So, I should disconnect 6.3V centre tap from ground and isolate?

Should I ground the negative leg of the last filter cap, as well as sending to heaters? I've added a ground to the circuit, is this the correct ground?
Should this be chassis ground or PS ground?

Here's the circuit:
6.3V Rectifier circuit.png
Cheers
Stephen
 

abbey road d enfer

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I’m going to try some low noise resistors to see if the hiss goes away.
Which resistors? Hiss, yes? You didn't mention that before. I thought we were dealing with hum...
I called the supplier for the grounding devices that were sent to me, and he said I should tack them to each of the three wires coming from the wall socket. When I get some time I’ll try it.
Don't expect too much!
 
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abbey road d enfer

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The cost of a couple of boards is $150,
Where? You could probably get 25 boards for that money at JLCPCB.
so I thought I'd do a P2P type build to make sure it's going to work. I haven't finished all the connections yet, but does this look ok so far?
Hard to say, but I don't see the connections between diodes, seems some are missing...
So, I should disconnect 6.3V centre tap from ground and isolate?

Should I ground the negative leg of the last filter cap, as well as sending to heaters? I've added a ground to the circuit, is this the correct ground?
You can do one or the other, center tap to ground or caps negative to ground, but not both.
Should this be chassis ground or PS ground?
PS ground is a better option.
 

morls

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Ok, here's my final layout:

P2P Rectifier 3.jpg P2P Rectifier 4.jpg P2P Rectifier 5.jpg

I thought I'd keep the centre tap grounded to PS star.

This might be a dumb question, but I'm not sure about the input wiring - the wires out of the secondary (6.3VAC) are both green, so there's no way to tell which is which. How do I know which wire to connect to red/black?

I think it's the same case where the heater connects back to the main board (I'll have to check under the terminal block) - there doesn't seem to be a +/- or high/low marking. I'm not sure what to do here...
 

abbey road d enfer

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Ok, here's my final layout:
Much better now! :)
This might be a dumb question, but I'm not sure about the input wiring - the wires out of the secondary (6.3VAC) are both green, so there's no way to tell which is which.
Being AC, there is no polarity. Whatever.
I think it's the same case where the heater connects back to the main board (I'll have to check under the terminal block) - there doesn't seem to be a +/- or high/low marking. I'm not sure what to do here...
It shouldn't matter. However sometimes it may make a difference in noise. You have to experiment.
 

morls

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Great, thanks. Hopefully I’ll get things up and running and be able to do some re-testing this weekend.
 
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solkatten

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You can ground - side of cap and disconnect CT. Or ground CT or you can elevate CT to 50vdc or somthing in that ballpark... Many options... If your dc is clean either way should work (y)
 

solkatten

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If you have trouble with noisy dc heather I would check the transfomer. Large current spike from rectifiers and big caps can make the trafo sing. Extra shielding on the PT have help for me... If the trafo sings you can detect it with a microphone or something... If its not that I would look at the grounding
 

Nbtone

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Which resistors? Hiss, yes? You didn't mention that before. I thought we were dealing with hum...

Don't expect too much!
I’m going to start with the resistor that connects the input to the grid and ground. Then I’ll go to the voltage dropping resistors that feed the anode. If that doesn’t do it I’ll just keep going into it deeper.
Those grounding devices are expensive, but I’m not expecting too much. They are supposed to keep all kinds of rf and other noise out. It’s going to be a month before I get to it.
 

Nbtone

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Which resistors? Hiss, yes? You didn't mention that before. I thought we were dealing with hum...

Don't expect too much!
When I put in the 600 v polypropylene capacitors and got rid of the elevated ground on the heater supply the hum went away, but there is still a low level hum. Without a safety ground the circuit is dead quiet.
 

abbey road d enfer

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When I put in the 600 v polypropylene capacitors and got rid of the elevated ground on the heater supply the hum went away, but there is still a low level hum. Without a safety ground the circuit is dead quiet.
Low noise resistors won't change a bit hum.
I don't want to dissuade you to experiment, but I know that low noise resistors count only when there's DC current through them, which is not the case for the input and grid resistors. It may make a difference in the anode.
 

abbey road d enfer

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As his alias implies, he's more mad than scientist.
Low noise resistors in anodes, yes, in cathodes maybe, in grids, why not but it doesn't change a bit.
Capacitor between grid and anode, restricts the bandwidth, which is more or less ok for a guitar amp, but for a mic preamp, no good.
Shielded cables help with hum but nada for hiss.
Claiming that low-noise tubes are necessarily low-gain is pure BS.
 

Nbtone

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As his alias implies, he's more mad than scientist.
Low noise resistors in anodes, yes, in cathodes maybe, in grids, why not but it doesn't change a bit.
Capacitor between grid and anode, restricts the bandwidth, which is more or less ok for a guitar amp, but for a mic preamp, no good.
Shielded cables help with hum but nada for hiss.
Claiming that low-noise tubes are necessarily low-gain is pure BS.
Thanks! I’ll keep this in mind when I finally get around to going through with this.
 

Nbtone

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As his alias implies, he's more mad than scientist.
Low noise resistors in anodes, yes, in cathodes maybe, in grids, why not but it doesn't change a bit.
Capacitor between grid and anode, restricts the bandwidth, which is more or less ok for a guitar amp, but for a mic preamp, no good.
Shielded cables help with hum but nada for hiss.
Claiming that low-noise tubes are necessarily low-gain is pure BS.
When I put in the 600v polypropylene caps I had to change the grounding scheme, too. I put all the power supply and signal grounds to one grounding point, starting from the furthest away and connecting each one in a line. Then I ran the panel mount grounds from the inputs and outputs to the pot(s) and the to the star ground. I kept the safety ground separate. This circuit is a grid leak bias tube circuit. The cap going to the grid is necessary.
 

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