• 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.

Tube rectifier versus 1200v SIC diodes?

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#62
I don't soft start this.

I have a 15A fuse on the branch circuit. It doesn't blow. I don't pay by peak demand. Why bother?
 

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#63
FlaCharlie said:
Andy - PSUD2 is now available for the Mac, depending on the operating system.

Download

I downloaded the native Mac version to my laptop, which is old but uses a slightly newer operating system than my desktop, which is an even older Mac Mini. I use the Wineskin software to make it work on the desktop, which is what I prefer to use.

It's been very helpful but I've only used its basic functions. Unfortunately, there doesn't seem to be a truly comprehensive, or even semi-comprehensive, manual.
Click to expand...

Duncan has moved the latest versions of PSUD II and support to a new site, which includes latest native MacOS builds

Log In
 
#67
andyjevans said:
I've logged in, and the Mac version is in the Files folder. I've downloaded it plus an update but I can't install it for security reasons because it's from an unapproved developer - will have to find out how to get around this.
Click to expand...
You may just need to change some settings in the Systems Preferences on your Mac or maybe your browser.

I seem to recall a message that warned that I was downloading an application from the internet and I had to click to allow it.
 
#69
Rod Coleman said:
>
...Now the supply looks like:

SiC Bridge → 27Ω [20W wirewound] → 820µF/550V → Cap-multiplier → 820µF/550V → small L → 100µF Audio MKP → PT...
Click to expand...


Hi Rod,

Three questions:

What is your definition of "small" in "small L"?

Is that final LC is your decoupling for the output stage for each channel?

For a PSU in a separate chassis, I assume you would make the split after the second big cap, adding a bleeder in the PSU chassis - correct? No need to add an additional cap like your previous iteration. (I am looking at your original version here: https://www.diyaudio.com/forums/tubes-valves/151421-26-pre-amp-452.html#post5252382 and a comment two posts later).

Thanks!

JM
 
#70
Hi John,

1. small L: 0.5-2H with <30Ω ESR.
2. I prefer separate supplies for each channel;

> For a PSU in a separate chassis, I assume you would make the split after the second big cap, adding a bleeder in the PSU chassis - correct?

Yes, that's correct!
 
#71
Rod Coleman said:
> Tube rectifiers have an internal resistance that will cause loss of supply stiffness, and since the capacitors cannot be large on a tube rectifier, the B+ voltage bounces with the music, which may impart a characteristic sound to it.


I wanted to look into this for my 300B-SE. Partly because of the lack of supply stiffness, and partly because of the relatively poor stability, lifetime, and sound of smaller high-voltage consumer-grade electrolytic caps.

My 300B-SE uses the oversized Sowter SA-08S (OT spec: 25W@20Hz, 0.5% THD), that allows much better bass than standard OTs for 300B.

SA08 SINGLE ENDED OUTPUT TRANSFORMER

With this OT, the 300B's internal anode-resistance of <800Ω would be better fed from a supply with bigger cap than even damper diodes can support.

A few years ago the Kemet ALS61 series caps were on sale for a low price, and I built a new supply based around the ALS61 550V 820µF parts. This means a reactance of near 10Ω at 20Hz - that's better.

The ALS & ALC series were acquired from BHC, and I know of these from designing them into professional equipment. They have a lifetime of well over 10000 hours at moderate temperatures, and the electrolyte has a neutral pH, so they do not degrade or need re-forming with anything like the same speed that consumer electrolytics do. Not to mention that 550V is able to withstand no-load conditions for many anode supply set-ups.


I built the supply with rectifiers in a bridge:
Wolfspeed C4D02120A, SiC Schottky Diode, 1200V 10A, 2-pin TO-220

the ramp-up current pulses are still a bit marginal for these, so the supply was run with a 35Ω-loop (including PT resistance), and little clip-on heatsinks for each diode (these need some mass, rather than surface area, since the real stress is at start-up). I used a cap-multiplier to give a slow rise-time, similar to damper diodes, to further reduce the initial diode-heat, and because I don't like abrupt application of HV to any circuit.


Now the supply looks like:

SiC Bridge → 27Ω [20W wirewound] → 820µF/550V → Cap-multiplier → 820µF/550V → small L → 100µF Audio MKP → PT.

This supply has been running for over five years, without problems, and with excellent consistency of sound. I don't believe it loses anything, compared to the polar opposite previous design: choke-input using a huge oil-filled 14H choke (from the Bletchley Park radio rally) , 6CJ3 dampers and LC stage filtering. It can play any kind of music, including pounding club 12" plates (that cause 300B-SEs to usually sound merely flatulant) - though mostly it plays symphonies.

Sound-wise I don't have a very definite preference, but I will say that using high-quality 550V ALS (now, choose ALC10 series) caps gives confidence that the sound is consistent over time that 47-100µF consumer caps do not give; but it seems that the ALC10 series is now available all the way down to 68µF (ALC10A680BC550) if you want to investigate these on a damper set-up.
Click to expand...
You say that the 8/20uF cap has reactance of 10 ohms at 20 hertz.
But you have decoupled this capacitor from the effective signal path via the choke (which has reactance cca 250 ohms at 20hz if its 2 henry). In this path there is an 100uF MKP cap which has reactance of 80 ohms.

so what is the difference between "effective AC path, the cap nearest the output transformer" vs "better energy storage of the 820uf caps " located further away from the OPT in the power supply?
wouldnt that choke prevent rapid discharge of the 820uf caps into the load if that would be necessary?
I dont have much education in this. Thank you very much.

Cheers, Michal

Thanks very much for clearing this out.

This cap has reactance
 
#72
The series resistance of the tube rectifier is much higher than that of any silicon rectifier type. It's about 30 ohms per plate with a 5U4, and less for an indirectly heated tube like GZ34. That's pretty mushy. The silicon of whatever type, is rock solid, with on resistances in the milliohms. After you get past that 0.5V to 2.5V or whatever drop, Bam! It's rock hard. There's no current modulated voltage sag to speak of at all.
 
#73
Hello. Just reviving this thread since I want to try out a SIC diode bridge for a preamp HT. The 1200v Cree/Wolfspeed C4D02120A is now unobtanium in the UK, so what I'm left with is a good number of C3D02060F – 600v, 4A. These are also hard to get, though Digikey has some. So the 600v part it has to be. I would use this with an input of around 0-230v AC (no centre tap). Current would be up to around 60mA, but could be as low as 12mA. I have some chokes 8H, 100mA. Also DC Link caps 12uF and 40uF, plus Kemet 550v electrolytics 68uF. So I want to be practical here and use a circuit that will be safe long-term. So what do I have to do?

  • heatsink?
  • add parts, if so what..... could anyone draw out a circuit? (?Eli?)
  • double them up, if so how?

I'm not so familiar with solid state as valves, so some targeted help would be great.
 
#75
Kay Pirinha said:
Is it still a preamplifier you're designing? Don't you have no 1N4007's? They offer plenty of headroom for this task.

Best regards!
Click to expand...
Hello! Yes, of course I have some 1N4007 - who doesn't! That's what I'm using now. Just want to see if I can hear any difference with SIC diodes, or any other diodes that might "sound" better than the trusted 1N4007s. Maybe yes, maybe no.
 
#78
trobbins said:
You've got some bridges so just use them. You aren't doing any double-blind testing, and nobody else is likely to follow you down your path, so there's likely no outcome for others as you aren't really doing any objective testing.
Click to expand...

Well, there's no outcome for you, but that doesn't mean others aren't interested in discussing SIC diodes. These have been discussed in other threads. A bit pointless in the sense that they aren't currently available, though, apart from the 400v ones I mentioned.

The fall back option as you say is just use a 1N4007 bridge or in fact UF4007 which is what I'm doing. It sounds OK to me, but we're all on the search for better, even if only marginally.
 
#80
Ah, that's interesting. Thanks for that. Unfortunately in the UK economics come into it. There are added charges for importing from the USA and a minimum order charge. In the UK I don't use Mouser or Digikey unless it's unavoidable. Usual suppliers here are RS and Farnell. I'd be interested in trying 1200v Schottkys but not at any price.
 
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