I think we will more or less be forced to use SMPS out of necessity. A variac is a choice too. The range/fluctuation will be too wide for transformers to be ignored.
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SMPS are not always suitable power sources, and the good ones are expensive. One thing for sure in my experience, old style brute force power supplies last forever. Not even close to true for SMPS, the capacitors they use get beat up in a small form factor and die. They need to lower operating temperatures to make them last, and use quality parts. I rebuild using Poly-Aluminum capacitors, which drops hash on the output as well.
Yep, spent the pandemic going through everything, the 'chopper' chips go and the caps. Replaced quite a few SMPS with coil transformers , that is what the mains network is designed for and works best with.
Difficult to better a potted toroid and a good hefty choke inductor.
...and that short termism argument that SMPS are cheaper, smaller more efficient, Oh the carbon foot print!
Not when they fail within a few years. Not if they destabilise sensitive digital devices. Not if they give you headaches or ear aches.
None of my coil PSU's have failed, They don't destabilise with digital devices, they don't give you headaches. Updating the noise filtering in some coil PSU's has been required in some areas, because of the huge uptake in use of SMPS's and the LF-MF hash they they inject back into the mains.
On a couple of occasions transformers lost the cohesion of their varnish and get noisy with the 50Hz , but that's across three decades! One of those I fixed recently by dripping superglue into the extra shield on an EI tran. A quieter transformer resulted.
Its possible to take some transformers that have lost cohesion in the windings to an electro motor refitting company and get them to dip it in their ultrasonic varnish bath and then heat cure them, what could be more environmentally friendly. Renewing something that was reasonably well designed in the first place.
Its an interesting fundamental to design a Power supply primarily with coils to achieve as much as possible, then add everything else.
Not when they fail within a few years. Not if they destabilise sensitive digital devices. Not if they give you headaches or ear aches.
None of my coil PSU's have failed, They don't destabilise with digital devices, they don't give you headaches. Updating the noise filtering in some coil PSU's has been required in some areas, because of the huge uptake in use of SMPS's and the LF-MF hash they they inject back into the mains.
On a couple of occasions transformers lost the cohesion of their varnish and get noisy with the 50Hz , but that's across three decades! One of those I fixed recently by dripping superglue into the extra shield on an EI tran. A quieter transformer resulted.
Its possible to take some transformers that have lost cohesion in the windings to an electro motor refitting company and get them to dip it in their ultrasonic varnish bath and then heat cure them, what could be more environmentally friendly. Renewing something that was reasonably well designed in the first place.
Its an interesting fundamental to design a Power supply primarily with coils to achieve as much as possible, then add everything else.
True, and that would be a relatively cheap option. Less convenient because every time you fire your system up (unless you let everything on 24/7) you have to check. My variac has a digital indication display for incoming and outgoing voltage, happy with that. The other option is go off-grid but then with different downsides. For consistently higher voltages (or lower) one could consider a buck transformer.
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Wow, you have a extraordinary power company. Mine, based on past experience, would hardly be that compliant.
I thought the generally accepted wisdom was that the electrolytic caps dry out or leak out, and after 30 to 40 years you need to recap, no?
Hi Gruesome,
The answer is .. it depends.
Larger electrolytic caps with terminals have more electrolyte inside, and they are sealed better. They can go bad, but most are perfectly fine. Just look at the ripple waveform with a scope. That will tell you. Smaller radial style caps with leads are not sealed as well, are smaller. They are more likely to go bad, but not always. The larger capacitor in the same voltage and capacitance is the better capacitor usually. Axial capacitors can outlast the newer smaller radial capacitors.
The running temperature and run time in hours determines how long a capacitor will last. Also the ripple current (current draw of the circuit). Never mind the initial quality of the part. For example, Pioneer used cheap parts, most caps will be bad in those. Things like coupling caps are not under stress as a rule, so most should be good as long as they were good quality to start.
The answer is .. it depends.
Larger electrolytic caps with terminals have more electrolyte inside, and they are sealed better. They can go bad, but most are perfectly fine. Just look at the ripple waveform with a scope. That will tell you. Smaller radial style caps with leads are not sealed as well, are smaller. They are more likely to go bad, but not always. The larger capacitor in the same voltage and capacitance is the better capacitor usually. Axial capacitors can outlast the newer smaller radial capacitors.
The running temperature and run time in hours determines how long a capacitor will last. Also the ripple current (current draw of the circuit). Never mind the initial quality of the part. For example, Pioneer used cheap parts, most caps will be bad in those. Things like coupling caps are not under stress as a rule, so most should be good as long as they were good quality to start.
You don't want series resistance in the main power feed to any amplifier. Same for power line conditioners, they don't play well with power amplifiers.
The reduction of inrush is always helpful, but it's better to use a resistor that is shorted out after < 1/2 second.
The reduction of inrush is always helpful, but it's better to use a resistor that is shorted out after < 1/2 second.
It is bit more complicated, if you find Frako electrolytic in your old equipment, like few yellow - gold ones on picture of Revox TT that I just plan to restore. Change them straight away, if not leaking they will tomorrow. Even I have to admit this machine is from 1980, still even Frako works 🙂
But if you see these inside, check manufacturing date, in 1979 (that is year 🙂 ) still up to specs! Probably it will be good for another 50 years...
Joke aside, these are extremes, usually electrolytic you will find are somewhere in between of these... Most will last long. But change them if it is easy, don't if they show no sign of deterioration and not easy to get out. Tantalum litycs last forever if applied in proper design, don't bother.
I did that, and the resistor became too hot and detoriated. Also the PT buzzed more than I liked. And you don't adress the possible problem with too high of filament voltages. For now a variac does the trick, but it hums as well, shame.
Hi Horneydude,
Use a bucking transformer connection to drop your AC voltage. Ideally, a 20 V filament transformer would work, 24 VAC would be more common and maybe cheaper. The secondary current rating should be well over your maximum so it doesn't run hot - or hum due to flux.
Humming may be due to either high current flow, or a slight effective DC on your AC mains.
Use a bucking transformer connection to drop your AC voltage. Ideally, a 20 V filament transformer would work, 24 VAC would be more common and maybe cheaper. The secondary current rating should be well over your maximum so it doesn't run hot - or hum due to flux.
Humming may be due to either high current flow, or a slight effective DC on your AC mains.
Thanks for the tips, I'll put it on my "to-do" list! Busy decorating my new home...🏠
The variac is rated for 1000W and the display shows 1.4 Amps. That's not it. Maybe DC but didn't measure (don't know how, with a scope?).
Probably not through a variac. Could be the bias current is higher than it should be. Check it.
Sometimes transformers simply hum. Just check all the bolts are snug, as are the ones that attach it to the chassis. You can press on the bell caps to see if they are vibrating.
Sometimes transformers simply hum. Just check all the bolts are snug, as are the ones that attach it to the chassis. You can press on the bell caps to see if they are vibrating.
No it's the variac that clearly hums. The tube amp is fine now, throttling the mains down. With the old Lafayette PT it always hums a little but no concern there, known issue with those (laminations vibrate a bit, you can rebuild them but it's o.k. for me).