I see two issues with it:
1) The voltage at the inputs of the 7806'es will be very close to the maximum rating of 35 V. Recall that 24 V AC when rectified will result in sqrt(2)*24 = 34 V unloaded and roughly 1.25*24 = 30 V under load. If that 24 V deviates even a little bit, you risk breaking the 7806.
2) At 2 A out (1 A per regulator), roughly 24 W - or nearly 50 W total for the two regulators - will be dissipated in each regulator. That will require a heat sink about the size of a 500-sheet ream of copier paper to dissipate safely. -- Or if you don't mind the noise, you can use one of those CPU coolers with a big fan on it. That should be able to get rid of 50 W.
If you insist on using the 24 V input supply, I'd probably be looking at a switchmode supply. Many of the ICs available require very few external components and are easy to get going. Check out the SimpleSwitchers from National for example.
Another approach would be to find a transformer with a more reasonable output voltage. A 10 V transformer would probably be fine.
Aside from these two issues, I don't see anything wrong with the schematic. I am assuming that you'll be feeding two separate heater strings with the two regulators. Don't connect them in parallel. They don't play nice if you do that...
~Tom
1) The voltage at the inputs of the 7806'es will be very close to the maximum rating of 35 V. Recall that 24 V AC when rectified will result in sqrt(2)*24 = 34 V unloaded and roughly 1.25*24 = 30 V under load. If that 24 V deviates even a little bit, you risk breaking the 7806.
2) At 2 A out (1 A per regulator), roughly 24 W - or nearly 50 W total for the two regulators - will be dissipated in each regulator. That will require a heat sink about the size of a 500-sheet ream of copier paper to dissipate safely. -- Or if you don't mind the noise, you can use one of those CPU coolers with a big fan on it. That should be able to get rid of 50 W.
If you insist on using the 24 V input supply, I'd probably be looking at a switchmode supply. Many of the ICs available require very few external components and are easy to get going. Check out the SimpleSwitchers from National for example.
Another approach would be to find a transformer with a more reasonable output voltage. A 10 V transformer would probably be fine.
Aside from these two issues, I don't see anything wrong with the schematic. I am assuming that you'll be feeding two separate heater strings with the two regulators. Don't connect them in parallel. They don't play nice if you do that...
~Tom
That schematic has numerous issues going on. 24 volts in should be the maximum, not the normal for a 6 volt regulated supply. The capacitors say 100p which can't be right. 1000uF is too little. 24 volts AC in would give you around 33 after the filter caps. Even a small load would generate tons of heat on the regulators.
Here's a better approach- if you're trying to heat several 6V heaters with the same current rating, configure the reg as a current source and put the heaters in series. You've got voltage to burn (literally).
Yeah, MUCH more filter capacitance is needed to knock down the ripple to something acceptable.
Yeah, MUCH more filter capacitance is needed to knock down the ripple to something acceptable.
How much current does the valve heater take? Look at the datasheet. For small signal valves it will often be 150mA or 300mA. All the valves in one series string should take the same current, otherwise you have to use balancing resistors.
Is this for your guitar amp, or something different? DC heaters for a guitar amp would be unusual. Only really necessary for a phono stage, and not even there with good valves and good wiring.
Is this for your guitar amp, or something different? DC heaters for a guitar amp would be unusual. Only really necessary for a phono stage, and not even there with good valves and good wiring.
I read the capacitance as 108 = 1000 uF. But whatever. It's hard to tell given the image quality. Depending on the load current, that might be OK, though, for a heater supply, I'd expect capacitances of at least 4700 uF if not larger. I generally don't like more than 0.5~1 V of ripple before the regulator.
~Tom
I wouldn't say that's the best option, though, it is a valid option.
You can also do the math and figure out what you need... I helped someone design a heater supply recently. You can find that info starting About Here in This Thread.
~Tom
A "monster" cap is hardly needed. Something like this would be fine.
An externally hosted image should be here but it was not working when we last tested it.
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