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Current rating for Sigma-11 power supply

post #1 of 8
3/22/10 at 10:23pm
Thread Starter 
I have gone through AMB's webpage for sigma11 linear power supply DIY project: The σ11 Regulated Power Supply

But there is no indication of what is the maximum output current can be achieved with the linear power supply. I understand that there is no current limiter built into Sigma-11 circuitry. Does it means that the output current is limited only by ratings of transformer, fuse, power transistors and heat sinks ? So I can scale the maximum output current with maximum ratings of these essential components ?

Basically I want to built a 30v/10A rectifier/regulator power supply module for my power amplifier. Already owned toroidal transformer with proper rating and aluminum casing. Since Sigma-11 has been used mainly for low current application such as headphone amplifier, I have to confirm that output current of 10A is achievable with this power supply module.
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post #2 of 8
3/23/10 at 12:22am
10A is too much to ask from the σ11. If you go through the calculations described in the "Board & heatsinks" section of the σ11 website you'll see why. Not to mention the current rating limitations of the rectifiers in addition to what you mentioned.
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post #3 of 8
3/23/10 at 1:03am
I was thinking about building either 6.3V (series) or 12.5V (parallel) o11 for a heater supply on a EHHA I balanced rig. Want some headroom to use some power hungry tubes (6H30's), so would 4-5A be asking too much? Would I probably want to consider a more robust heatsink alternative?
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post #4 of 8
3/23/10 at 1:57am
Again, please work through the MOSFET junction temperature calculations found at the σ11 website and convince yourself whether this is a tenable use. Increasing the heatsink size helps, but ultimately you're going to find that the thermal resistance of the MOSFETs' TO-220 package is a bottleneck.

Personally, I think that σ11 is not a good use for tube filament heaters. The performance benefits of the σ11 would be largely irrelevant, but the drawbacks of a linear regulator (inefficiency and heat dissipation) will be all there. For something that requires such high currents, I'd look at a switch mode regulator.
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post #5 of 8
3/23/10 at 2:01am
Quote:
Originally Posted by Horio View Post
I was thinking about building either 6.3V (series) or 12.5V (parallel) o11 for a heater supply on a EHHA I balanced rig. Want some headroom to use some power hungry tubes (6H30's), so would 4-5A be asking too much? Would I probably want to consider a more robust heatsink alternative?
Horio, I’m doing the same, 8A is the limit of the rectifiers.
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post #6 of 8
3/23/10 at 2:58am
Quote:
Originally Posted by johnwmclean View Post
Horio, I’m doing the same, 8A is the limit of the rectifiers. I have a custom sumR transformer rated at 30VAC, with a single 11V secondary. As I’m going balanced I be running 6.3V from each output on the σ11 directly to each EHHA board.
From the EHHA thread, it sounds like the o11 may be a bit overkill for the heater supply, but its considered the "ultimate" solution. I was looking at some other setups, but in the end the o11 is not that much more expensive. Sounds like I need to do the calc and figure out what type of heatsink will be required. I guess I'll look into some alternatives a little more too before I start buying parts.

How much are those custom sumR transformers? I've been thinking about getting 3 of those made (2 for the dual mono o22's, and 1 for the o11). People seem to think they are nice.
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post #7 of 8
3/23/10 at 3:59am
Quote:
Originally Posted by amb View Post
Personally, I think that σ11 is not a good use for tube filament heaters. The performance benefits of the σ11 would be largely irrelevant, but the drawbacks of a linear regulator (inefficiency and heat dissipation) will be all there. For something that requires such high currents, I'd look at a switch mode regulator.
Ti, I agree a lot of the benefits would be mute, however the competitive pricing of the σ11 puts it up against some pretty average regulators.

There are lower powered tubes like 6GM8’s and would work out around 2.6A total in a balanced EHHA build.
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post #8 of 8
3/23/10 at 5:05am
Quote:
Originally Posted by Horio View Post
How much are those custom sumR transformers? I've been thinking about getting 3 of those made (2 for the dual mono o22's, and 1 for the o11). People seem to think they are nice.
Shipping kills me as down under, send Richard an email, the guy quotes real fast and is a very good communicator.
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