Good Day,
I have designed and tested a valve heater regulator using a LM317 but am keen to use a LDO regulator (< .75V DO) to reduce both the component count and power dissipation across the regulator. Only caveat is that the heater voltage is elevated to 140V. So does anyone have any suggestion for a suitable regulator? The heater voltage is 6.3 V and there are two in parallel ie .6A although I can run them in series (12.6V @.3A).
Also what rectifier diodes are recommended, anything special or would the UF4007 suffice? One with a low forward voltage drop would be of benefit.
Thank you,
I have designed and tested a valve heater regulator using a LM317 but am keen to use a LDO regulator (< .75V DO) to reduce both the component count and power dissipation across the regulator. Only caveat is that the heater voltage is elevated to 140V. So does anyone have any suggestion for a suitable regulator? The heater voltage is 6.3 V and there are two in parallel ie .6A although I can run them in series (12.6V @.3A).
Also what rectifier diodes are recommended, anything special or would the UF4007 suffice? One with a low forward voltage drop would be of benefit.
Thank you,
If you are running the heater from a mains-voltage input, the variation due to mains tolerance might be as much as ±1.3V (UK tolerance is ±10%), so trying to take the dropout all the way down to 0.7V is likely to be disappointing!
For voltage-regulating indirectly heated valves, LM317 is probably best in any event. The LDO type are PNP (or P-ch) output for positive voltages, meaning more care is needed for stability checking.
Floating the heater on 140V bias is no problem - just let the trafo winding and rectifiers/caps float, and remember not to share the 12.6V output with anything else.
For voltage-regulating indirectly heated valves, LM317 is probably best in any event. The LDO type are PNP (or P-ch) output for positive voltages, meaning more care is needed for stability checking.
Floating the heater on 140V bias is no problem - just let the trafo winding and rectifiers/caps float, and remember not to share the 12.6V output with anything else.
FWIW, for quite some time, I've advocated "full wave" voltage doubling "6.3" VAC with Schottky diodes and regulating with either a 7812 or 7912 regulator IC. Forward drop in Schottky diodes is "0.5" V. The feedback from the field for the method has been highly encouraging.
(6.3 - 0.5) (2) (21/2) = 16.4 Plenty of headroom for mains fluctuation is present.
(6.3 - 0.5) (2) (21/2) = 16.4 Plenty of headroom for mains fluctuation is present.
I have designed many valve amplifiers, mixers etc.
I have yet to find the need for DC heaters.
On my first ever valve mixer design I got hum so changed to a DC heater.
Made no difference at all as the problem was elsewhere.
The only time dc heater is needed is for directly heated valves.
Hum can be down to:
1/ Unscreened input cables.
2/ Interference from transformers, high voltage AC close tracks.
3/ Long tracks/wires to input valves.
4/ Poor grounding. Star grounding should be used where possible.
5/ No earth.
6/ heater not dc elevated.
I have yet to find the need for DC heaters.
On my first ever valve mixer design I got hum so changed to a DC heater.
Made no difference at all as the problem was elsewhere.
The only time dc heater is needed is for directly heated valves.
Hum can be down to:
1/ Unscreened input cables.
2/ Interference from transformers, high voltage AC close tracks.
3/ Long tracks/wires to input valves.
4/ Poor grounding. Star grounding should be used where possible.
5/ No earth.
6/ heater not dc elevated.
Well, I once chased a nasty rattle on the tweeters. Using an ECC81 LTP (H-C allowed voltage 90V) with elevated cathodes at 170V, I reached for this MPSA42 THINGY by M Jones. That was the source because I probably misused it at too high HT. Turning to DC and lifting through two resistors and cap cured the rattle promptly. No AC residue on my clean DC 🙂
The last buzz I had was from switching noise from 1n4007's.
Changed to Schottky's and the problem vanished.
Changed to Schottky's and the problem vanished.
Since the OP did not indicate that he is designing a mixer or a simple amp, and perhaps he is working on something more sensitive like a microphone preamp or an RIAA phono preamp, perhaps your experience isn't all that relevant.
Yes, I did omit the use, it is for a Phono Amp.
I am also using the THINGY designed by Morgan Jones to obtain the elevated DC voltages I need.
I am also using the THINGY designed by Morgan Jones to obtain the elevated DC voltages I need.
For diode selection with low voltage Schottky diodes, development is rapid enough that what would be recommended now may not be available in a few years.
In general, the TO-220 packaged diodes with insulated bodies are reasonably easy to work with. Also I would generally look at the diodes with the highest current rating in the applicable voltage range to find those with the lowest forward voltage drop. This can be a bit of a process!
In general, the TO-220 packaged diodes with insulated bodies are reasonably easy to work with. Also I would generally look at the diodes with the highest current rating in the applicable voltage range to find those with the lowest forward voltage drop. This can be a bit of a process!
What is the advantage of the 10nF over the Schottky's? It seems contra-intuitive to the use of low capacitance semi's: when the diode is switched off the cap conducts any hash. If the transformer is too exited a snubber to the secondary would be more appropriate.
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This is just an idea.
There was a schematic posted by Mona before in a different topic, cannot remember which one. I ran with that and this is the result, it works in simulation and i have a nearly completed design for it that is through hole somewhere.
The PNP TTA can be a plain BD140, and you may need to revisit some of the component values to get it to work. For the pass transistor you can try 2SC6144 or a logic level FET.
For diodes i wouldn't stress it too much, SB540 skottkeys is what i normaly use for this kind of thing.
There was a schematic posted by Mona before in a different topic, cannot remember which one. I ran with that and this is the result, it works in simulation and i have a nearly completed design for it that is through hole somewhere.
The PNP TTA can be a plain BD140, and you may need to revisit some of the component values to get it to work. For the pass transistor you can try 2SC6144 or a logic level FET.
For diodes i wouldn't stress it too much, SB540 skottkeys is what i normaly use for this kind of thing.
Attachments
Good Morning All,
Thank you for your comments, suggestions and advice. I have moved the design forward and am awaiting the arrival of some components to test out some of the ideas I have. I can always fall back to using the LM317, which I have working for both the standard and elevated heater supplies (the pcb is also designed) but felt there ought to be a more efficient way to generate the DC heater voltages using contemporary components.
Should keep me entertained for a few evenings!
Regards,
Thank you for your comments, suggestions and advice. I have moved the design forward and am awaiting the arrival of some components to test out some of the ideas I have. I can always fall back to using the LM317, which I have working for both the standard and elevated heater supplies (the pcb is also designed) but felt there ought to be a more efficient way to generate the DC heater voltages using contemporary components.
Should keep me entertained for a few evenings!
Regards,