• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Anyone in the L.A. area with scope willing to troubleshoot?

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#21
Just to be clear, the top schematic on attached shows what I mean.

If that works, you could consider using the supply in the bottom schematic in attached figure. It'll provide much, much greater ripple attenuation due to the LC filtering. You still need the 4.7 kOhm resistor to drop the voltage from 250 to 200, though. Hence, the last RC filter stage.

~Tom
 

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#22
Thanks again Tom. I do want to try and keep the choke loaded supply though. But let me exhaust all possible reasons this is getting polluted with ac and then explore other psu layouts like what you drew out. Really appreciate all your help and time. Too bad we don't live closer. It would be great to know a local DIYer!
 
#23
You're quite welcome.

I understand your desire to keep the choke supply. If the experiment with the cap input supply results in lower ripple and less hum, at least we then know that we need to design a choke input supply with lower ripple.

I hear that low-current choke supplies can be troublesome -- but that may also be an opportunity for new - more specific - questions and new learnings. One thing to consider should the choke supply idea be abandoned would be to use a CCS and a shunt regulator. From what I hear that comes quite close to the choke input supply in terms of resulting amp sound quality. But of course each amp is different and people perceive sonic differences differently. In other words, your mileage may vary.

I'm curious to hear what you find out with the cap input experiment.

~Tom
 
#24
tomchr said:
You're quite welcome.

I understand your desire to keep the choke supply. If the experiment with the cap input supply results in lower ripple and less hum, at least we then know that we need to design a choke input supply with lower ripple.
Click to expand...

Absolutely correct. I completely understand.

tomchr said:
I hear that low-current choke supplies can be troublesome -- but that may also be an opportunity for new - more specific - questions and new learnings. One thing to consider should the choke supply idea be abandoned would be to use a CCS and a shunt regulator. From what I hear that comes quite close to the choke input supply in terms of resulting amp sound quality. But of course each amp is different and people perceive sonic differences differently. In other words, your mileage may vary.

I'm curious to hear what you find out with the cap input experiment.

~Tom
Click to expand...

I promise to let you know. The preamp sounds incredible so I want to be careful not to lose the sound with the ripple. 😀
 
#26
phrarod said:
Choke loaded 5AR4
Click to expand...

I'm not saying it can't be done. I have never built a choke input supply, so I have no personal experience with it. But I frequently see competent builders in this forum warn about the design challenges of choke input, low current supplies. Thus, I suspect that the supply in your amp will be a significant challenge to design if you stick with a choke input supply. That's all....

But starting a thread - or searching through the forum - for advice and common pitfalls of low-current choke input supplies would seem worthwhile. If you decide to ask questions about it, I suggest that you be specific and list your specifications; 12 mA, 200 V, choke input.

But let's try with cap input first. If it has no effect on the hum, we're back to square one. Hopefully, it will have an effect. Then we can go off and design a power supply...

~Tom
 
#27
Thanks again Tom. Makes sense. Through a contact I found out Bob Hovland lives in my neighborhood. He wants me to call him on Tuesday.

I did some more testing and grounded one of the transformers I mentioned was carrying AC on the body but it had no affect on hum of ripple.

I need to take a break for a couple days before I screw it up. Something my wife demanded I not do. 🙂
 
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