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Planning to build benchtop 500V tube PSU, help needed.

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H713:

--- Quote from: T3sl4co1l on June 10, 2019, 05:52:11 am ---Also 6BG6 (sweep version), 807 (coke bottle, RF), 1614 (metal, RF), etc.

Mind that new "6L6s" are all over the place, at least in the cheaper brands.  Everyone makes 6L6GCs, because of course they do, but they don't all handle 30W like a 6L6GC is supposed to.  Derate generously (say 30-50% below rated), treat them more like 6L6GBs if that.

Even then, the material quality is poor, so don't expect great lifetime.

That's a nice advantage to industrial and PQ types: better materials, higher ratings, longer life.  A $100 tube that lasts 10khr is a better deal than a $50 tube that lasts less than 5k -- assuming you have the budget to do so, and will be using the equipment frequently.

Or conversely, if not, it may actually be a better deal to use the cheaper part, and then maybe keep spares handy, accepting that when (not if) the originals fail, you'll have the annoyance of changing them out, but you won't be SOL for a week awaiting delivery of new parts.

One last thing.  Mind that poorly constructed tubes are more likely to melt or arc over and fail shorted.  Have some protection method in place (a crowbar?) to deal with this.  It's most likely to happen at the lowest output voltages, where the load will be most vulnerable to a surge to full B+...

Tim

--- End quote ---


Just my personal experience, but I've found that the new production 6L6GCs are pretty good. They've certainly gotten better over the last few years. Buy sets that have been burned in, you should be fine. I've pushed some of them pretty hard, and they take it. I'm running Tung Sol (new production) 6L6GC-STR tubes in one of my power amps, and they've been rock solid for over a year (figure five hours a day?), running at about 28W plate dissipation.

Keep in mind what most of these are being used for- Guitar amps. Lots of them push tubes really hard, and in a lot of cases they are sitting just a few inches away from one or two twelve inch speakers that are producing earth-shattering SPLs. And remember- a lot of these amps are being blasted for quite a few hours at a time, and they aren't being babied. Your bench power supply will be sitting on a bench, away from speakers, and you probably won't be running them any harder.

As a contrast, when I built my latest power amp using 1625 tubes (12V heater version of the 807, itself a version of the 6L6), I had two NOS RCA tubes and one NOS National Union tube that shorted after a total of about eight hours of usage running at about 19W plate dissipation.

In addition, a lot of the alternative tubes that could be used have dwindling supplies that I would prefer to see used to keep existing equipment operating. Aside from my personal feelings on this subject, there is nothing more frustrating than having a piece of gear that uses an unobtainium part with a finite lifespan. Just ask owners of U47s and U48s how they feel about the supply of VF14Ms.

Also, I would definitely suggest implementing something to minimize how much power is dissipated in the series pass elements. This could be as simple as a carefully chosen dropping resistors, or as elaborate as a variac controlled by a servo motor. I can attest that the later does work quite well. If you use the Antek toroid I suggested, you have a pair of HV windings. Switching transformer taps is a pretty easy way to handle this issue. That combined with a simple crowbar would go a long way to improving the safety of this power supply, though one must always remember that anything that can source 500V at this level of current can easily kill you.

001:
Any news?

geggi1:
If you want at rough and simple 500DCV PSU without any features the resepy is simpel.
- One transformer with secondary voltage of 350V.
- Four diodes capable of at least 500V. Recomend 1N4007 or better.
- Electrolytic capacitors with a rating of at least 500V (go for at least 600V capacitors) with plenty of capacitance

Optional
- One variac to get ajustable voltage.
- Toroide bifilar winded core for noise reduction.

Rectify the 350VAC with a four diode rectifier bridge. Smooth the voltage with plenty of electrolytic capacitors. Add a bifilar wounded inductor to reduce the noise. The variac can be placed in front of the 350V transformer to have some voltage regulagtion.
If avalable get a 230/380 transformer this will be avalable at companies like RS, but you will have to use a variac to ajust the voltage dowin to 500v

001:

--- Quote from: geggi1 on August 17, 2019, 06:33:18 pm ---If you want at rough and simple 500DCV PSU without any features the resepy is simpel.
- One transformer with secondary voltage of 350V.
- Four diodes capable of at least 500V. Recomend 1N4007 or better.
- Electrolytic capacitors with a rating of at least 500V (go for at least 600V capacitors) with plenty of capacitance

Optional
- One variac to get ajustable voltage.
- Toroide bifilar winded core for noise reduction.

Rectify the 350VAC with a four diode rectifier bridge. Smooth the voltage with plenty of electrolytic capacitors. Add a bifilar wounded inductor to reduce the noise. The variac can be placed in front of the 350V transformer to have some voltage regulagtion.
If avalable get a 230/380 transformer this will be avalable at companies like RS, but you will have to use a variac to ajust the voltage dowin to 500v

--- End quote ---

Honey. It is EE forum.   :-DD Everybody can build simple Herz bridge here
The story of HV  benchtop tube PSU is always WERY tricky. So any benchtop  PSU requires constant voltage and constant current modes. And big caps at lab PSU output is BAD idea  :palm:

TERRA Operative:
I still got all the parts here for the unit as it is in the first post. I'll have to filter through the thread and see what mods I want to use for my final design...

I haven't done any actual work on it yet, I keep getting distracted with the next shiny thing, but once my current project (A Fluke 332D restoration) is done, I'll get back onto this one for sure.

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