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Registered Member #4081
Joined: Wed Aug 31 2011, 06:40PM
Location: UK
Posts: 139
I think we need to know a few more specifications: What amount of current do you need? Are you happy to work from the mains? Are there any cost/size limitations? Also here is an interesting site about switch mode PSU design
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Gren wrote ...
Just pick something large enough so that Xc doesn't become an issue. This isn't too efficient for large loads though.
You might want to re-think this, Gren, as the circuit as you have it will do nothing at all.
What you have drawn shows a single cell battery charging two polarized capacitors in series. When they are fully charged - almost instantaneously in your circuit - no further current will flow.
Your mention of Xc suggests you may have been thinking of an AC circuit, rather than direct current flowing from a battery.
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
If you are new to this "game" i.e. playing with tube supplies, WHATEVER YOU DO, DO NOT RECTIFY THE MAIN LINE!!!!
YOU ARE NOT PROTECTED!!!
I have drawn over 200A from a 35A breaker for short duration, and that is more than dead, if you get my drift.
Find a small power transformer like a 220-0-220, and rectify it like the circuit, and you can control it with your variac to where you want it. AND... AND, it is current limited to the current the transformer can supply. A Fast Blow fuse on the high side is a good idea too.
Registered Member #1951
Joined: Sun Feb 01 2009, 01:59PM
Location:
Posts: 105
sorry, for the waiting. :) no I am not really new to playing with tubes so i know i need to be protected from mains. I've got a basic amp circuit working now. But I wanted to build something useful (for fun and learning) and yea.
so: the current probably not more then a amp. (probably not even more then 500 Milli amps)
2. Got a lot of tubes. but the tubes are a side track of the project the main reason for building is having a supply :)
3. To power the circuits I build with my tubes or even other circuits that don't include tubes.
4. Can spend some money, but I wanted to recycle some old components I got laying around. (a few ups boards and mosfets and more). I don't really care for the complexity of the circuit as long as I do have fun building it :)
Hope I been clear, if not I am sorry and I'll try to explain it again.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Duality wrote ...
sorry, for the waiting. :) no I am not really new to playing with tubes so i know i need to be protected from mains. I've got a basic amp circuit working now. But I wanted to build something useful (for fun and learning) and yea.
so: the current probably not more then a amp. (probably not even more then 500 Milli amps)
2. Got a lot of tubes. but the tubes are a side track of the project the main reason for building is having a supply :)
3. To power the circuits I build with my tubes or even other circuits that don't include tubes.
4. Can spend some money, but I wanted to recycle some old components I got laying around. (a few ups boards and mosfets and more). I don't really care for the complexity of the circuit as long as I do have fun building it :)
Hope I been clear, if not I am sorry and I'll try to explain it again.
Golly, 500 mA HT is a huge power supply by thermionic standards, where small signal AF and RF valves typically draw anode currents of 3 - 10 mA, with popular AF output valves like 6V6 drawing 40 mA or so at 250V, and even big transmittter valves like 813 requiring just 200 mA at 2 kV.
As you don't say what you are intending to do, it's difficult to know what to suggest, but valves of the type that will be happy operating at 150V usually have very modest anode currents, by which I mean in the low mA regime.
PS: Variable HT supplies were uncommon in the valve era due to the complexity, cost, and cooling that such required. The approach used in consumer electronics, radios for example, was to have a single HT line from which anode supplies would be derived by dropping resistors - suitably decoupled to Earth - with potential dividers setting the voltage for screen grid supplies. Look on ebay for second-hand amateur radio manuals of the 1940s, '50s and '60s, and you will soon know more about thermionic valves than you ever really wanted to know!
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
I've been helping a guy design a small tube amp so this Heathkit was more than sufficient to supply his needs.
It's a PS-4, I have the schematic somewhere, but that should give you a start, just look for Heathkit PS-4 schematic. There are a couple of sites that have a free schematic posted, and you can copy it from there.
The PS-4 supplies up to 100mA regulated, using 2 6L6 tubes in parlallel as the pass regulator. If you wanted more current, you could substitute the tubes in your design to be anything really, you could use KT120's if you liked, although I think that is somewhat wasteful. You could use several 6L6's in parallel to handle the current you need to supply.
500mA is quite a supply indeed, but a 100W Fender Twin transformer will supply 300mA max for short durations, so it's not like this kind of thing is unheard of. My Twin build will pull 250mA full swing, but it is a 100W amp.
If you're building single ended tube amps that are less than 30W, all you'll really need is maybe 150mA max.
Here's a pic of my "el cheapo" supply. It is fixed output, but if I need less voltage, I just put it on the variac, which is easy.
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dc high voltage supply (120 ~ 160).
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