TL783 regulator is one of the favorite regulators I like apart from the usual LM317 family members. This fits into our topic of today – inexpensive, small size & simple voltage regulator for tube line stage or phono stage when extremism in my blood stream falls asleep. Sometimes I’m really a lazy cheapo!
Vacuum tube-o-philes might despise the use of solid-state regulators though but I’ve good experience using them at various parts of the circuit. No doubt other variants could be sonically superior but these do provide a good alternative for cost, size and simplicity reasons.
The TL783 could be for the B+ supply for tube line stage, phono amplifiers or even power stage. Due to the low noise and ripple requirements for the above first 2 applications, not to mention the current capability, using TL783 is not such a bad choice after all.
Other than for regulating the B+, bias or filament supply, it can be used as current source or sink, and has may other functions. For this article, let’s just focus on voltage regulation.
The maximum voltage limit of 125Vdc for the TL783 is not considered very high and we have to select the tubes that could work well and sound good under such conditions. What comes to my mind would be the ECC88, 6DJ8, 12AU7 and etc. That reminds me of the ECC86 that is even better suited as it is meant to work with batteries!
TL783 Voltage Regulator.
The above shows the schematic for making the TL783 as a voltage regulator. Since in a tube amplifier, we know what Vo (output voltage, B+) we want, we can rearrange the formula to make it easier for us to calculate R2. Vref is pretty much fixed at 1.25V by design.
R2 = ((Vo/Vref) – 1) / R1
Assume that we want a B+ of 100V, we can substitute the numbers in to get R2.
R2 = ((100/1.25)-1)/82 = 6478 Ohm
Turning the potentiometer would get us the voltage needed. You can substitute the potentiometer with a fixed resistor if you want.
Above is a sample B+ power supply. The preceding stage to the voltage regulator could be tube or solid rectified; choke input or cap input; bridge or full wave rectified; and etc. The TL783 will have low enough power supply ripple to power the line or phono stage. In addition, since it is low cost and small, one can really have dual-mono voltage regulated PSU for the amplifier for absolute channel separation!
To have the smallest size possible, use solid stage rectifiers and replace the choke with a resistor. The capacitance can be reduced significantly compared to not using any active voltage regulation.
It is simple, fool proof, small in size, inexpensive and works well!
We shall talk about using TL783 regulator and LM317 regulator as current regulator next.
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