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| Voltage regulator tubes vs zeners (tubes has BETTER stability) |
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| 001:
Hi I`m chocked with fact what Voltage regulator tubes has BETTER temperature stability than silicon zeners at same voltage :o But it can float a little What the way to replace rare VR tube with zeners without stability missing? |
| SeanB:
Not surprising, though you can get much better stability using an amplified low TC zener, most commonly 6V8, or using a TL431 and appropriate cascoded transistors to get the shunt voltage across the actual TL431 down to somewhere in it's operation range, probably by using a 6V8 zener and a high voltage transistor to do that. |
| T3sl4co1l:
The TL431 is probably less noisy. :-DD (Bandgap references, like TL431, are notoriously noisy, as solid state signals go; but glow discharges are so awful, they've been used as noise sources (with some tweaks, namely, magnetic bias).) Also, you seem to be under some illusion as to the value of VR tube stability -- few tube circuits needed it, indeed few circuits in general need regulation. It's just done as a matter of course because, if we're starting with a 90-250VAC line spec, we can't very well work directly with that, and the output is usually variable anyway (e.g. flyback power supply) so the output must be stabilized with feedback regardless, and we might as well use a puny cheap TL431 or the like, as an error amplifier, to provide that feedback. The fact that a TL431 happens to give a <= 5% precision (and typically ~0.1% stability) is practically accidental, but we aren't going to argue with results that are both good and cheap. The average tube circuit consists of a few amplifier stages, which will amplify equally well over perhaps a +/- 20% range of supply, give or take reduced gain or maximum power output at the low end, and reduced lifetime at the high end (excessive plate or heater dissipation; cathode wear). Unless you have 3rd-world mains (in which case the bigger problem is usually just that it's terribly unreliable..?), an unregulated, mains-derived supply will do fine. :-+ Tim P.S. A motor vehicle gets "chocked" to prevent it from rolling away. Short, harder 'ch'. You might be shocked (soft 'sh') to discover something though. English, right?... |
| 001:
thank you for your wisdom! How would you recommend replacing the VR tube with TL481? Any practical schematics. lincks. etc? |
| duak:
VR tubes also have a voltage spike when starting. This is because the gas must first be ionized at a higher voltage before the tube starts regulating. If memory serves a 105 V VR tube needs 130 V to strike and start conduction. |
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