Pre-Amp Build

Dilemma #1. I didn't know whether to post this in the PSU thread but since it applies here - here goes.
When I plug in the numbers in the schematic PS into PSU, I just get 130V out and huge ripple. I added the heater elevator/bleeder into the CC sink at the end. I need more like 300V to use the glow tubes and the 5R4gyb even in hybrid mode is even worse obviously. I'm sure I'm doing something wrong, but what? I'm in pretty good shape if I leave out that 4.7K resistor and the ripple gets far better if I substitute choke instead of the resistors.



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The number one thing is that the VR tubes will draw the correct DC current to sit at ~150V. In your sim that would mean 35mA of current instead of 40mA. To get an accurate idea of what the ripple would be with the regulator tube in there, you're not going to be able to use PSUD.
I would suggest building it as drawn, then returning if there is an issue with 120Hz noise. The 4.7K resistor can be replaced (later, not now) with a CCS for enormous PSRR, but I wouldn't do that unless you need it or you get bored down the road.
 
Also 5R4s don't really belong in a project like this.

You could use a 5AR4 and swap out the 270 ohm resistor for a 5H choke with lower DCR, say a Hammond 159P or a Hammond 156M.
 
I'm late to the party, but I don't understand why you're using a relatively high voltage power supply and then burning off most of the power as heat in that last 4.7K resistor. Using the same transformer that you already have, I'd using half of the secondary, i..e 125v instead of 250v and then change R2 from 4.7K to roughly 560ohms. Instead of dropping from 330v to 150v, you'll drop from 180v to 150v. The power dissipated in R2 will drop from 7.5W to 0.6W, which will make it much easier to manage. And the preamp will behave exactly the same since it will still have a B+ of 150v from the OD3.
 
Since it's hard to do a full wave bridge with tubes, you can use a hybrid rectifier with tubes on the positive side and solid state on the negative side. Something like this.

Hybrid-Rectifier.gif
 
I'm late to the party, but I don't understand why you're using a relatively high voltage power supply and then burning off most of the power as heat in that last 4.7K resistor.
Well, we need enough voltage to ignite the regulator tube, and higher impedance between B+ and regulated B+ will increase power supply ripple rejection.

Using the same transformer that you already have, I'd using half of the secondary, i..e 125v instead of 250v and then change R2 from 4.7K to roughly 560ohms. Instead of dropping from 330v to 150v, you'll drop from 180v to 150v.
What happens if line voltage is a little low? Even at 180V you are below the minimum power supply voltage to get an 0D3 to strike, so it's entirely possible that you could build that and it simply wouldn't work. It would also be a bit noisier.
 
Well, we need enough voltage to ignite the regulator tube, and higher impedance between B+ and regulated B+ will increase power supply ripple rejection.


What happens if line voltage is a little low? Even at 180V you are below the minimum power supply voltage to get an 0D3 to strike, so it's entirely possible that you could build that and it simply wouldn't work. It would also be a bit noisier.
I do agree that the 269AX will be marginal with a tube rectifier but probably would be fine with solid state rectification.
A 150v secondary such as 1/2 of a 269BX would work just fine with a tube rectifier.
It still offends my sensibilities to burn that much power in a dropping resistor, so if it were me I'd find a more appropriate power transformer and minimize that last resistor so it doesn't generate so much heat. Something like this Antek transformer would work quite well with a hybrid bridge.
 
It still offends my sensibilities to burn that much power in a dropping resistor, so if it were me I'd find a more appropriate power transformer and minimize that last resistor so it doesn't generate so much heat.
I find the power to be far less problematic than overly tight compliance. I have done designs like this where the compliance is pretty tight, and it's a big letdown when you fire things up and the 0D3 never ignites. Once you've done that and had to start over with a power transformer providing higher voltage, the extra dissipation doesn't seem like that big of a deal.
 
I'm ordering the last few things to bread board. What can I use to simulate the load on the PS circuit? I want to test every thing including the glow-tubes but not the entire circuit.
I think I need a 4.7k resistor of ? wattage. Correct?
I know I can just run it but I want to test it under load. I do have a speaker load box I made with 8 & 16 ohm taps
 
I'm ordering the last few things to bread board. What can I use to simulate the load on the PS circuit? I want to test every thing including the glow-tubes but not the entire circuit.
PSPICE.

I think I need a 4.7k resistor of ? wattage. Correct?
I thought a 4.7K/20W resistor would be easy to find. Instead, you could just use a pair of paralleled 10K/10W resistors and that should work.

I know I can just run it but I want to test it under load. I do have a speaker load box I made with 8 & 16 ohm taps
I'm not sure what you're asking here...
 
I'm unclear as usual. I'm wondering if there is a resistor I can place across the +150V and PSU ground so I can confirm voltages and chect the glow-tube function of the PSU alone?
I thought I figured I needed a 4.7K ohm resistor
R= .032A/150V = 4.7K
Does this see correct for a stand-in for the rest of the pre-amp circuit?
I believe I need to have a 5W or greater resistor.
The speaker load thing was something I had and was wondering if I could use it somehow for the above. But I realize my error.
 
You can just run the raw supply, dropping resistor, and 0D3. You don't need anything to stand in for the rest of the circuit, the 0D3 will just draw any current that's absent to maintain 150V on the regulated side of the dropping resistor.
 
Thanks guys. No matter how I try my PSUD sim does not look pretty. I'll just BB it and see. I just ordered a bunch of resistors and a choke as well as a 5V transformer so I can experiment with both bridge rectifier and hybrid tube. I'm hoping PSUD is a dud in this simulation as I'm only at 130V.
 
I know you said to avoid the 5R4 rectifier but this seems to work OK doesn't it?

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