I made a board for a project and ordered a bunch of them.
It takes 6.3V from the heater windings and makes 12V for controlling a relay etc using a Delon doubler and a 12V regulator such as MC29300 or LM7812. I use it with a dual winding 6.3V transformer using one winding for DC control, and the other for the 6.3V the biasing board requires.
If anyone wants any I'll offer them for 2$ each plus mail.
Cheers.
Koda
It takes 6.3V from the heater windings and makes 12V for controlling a relay etc using a Delon doubler and a 12V regulator such as MC29300 or LM7812. I use it with a dual winding 6.3V transformer using one winding for DC control, and the other for the 6.3V the biasing board requires.
If anyone wants any I'll offer them for 2$ each plus mail.
Cheers.
Koda
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"Great minds think alike." 😉 I'm a long term advocate of "full wave" doubling 6.3 VAC to obtain regulated 12 VDC heater supplies. Low forward drop Schottky diodes in the doubler avoid dropout exposure in low cost 7812 3-terminal regulator ICs.
Yes, it would work for that too! Since the current limit is about 1A with a 29300 (not much room for heatsink) I figure that's for a pair of 6SL7 or something?
I used SB1100 and an MC29300 myself since I had them... The larger the drop in the diodes, the less work the regulator does, right? It's only there since I read 18.9V with no load 🙂
I used SB1100 and an MC29300 myself since I had them... The larger the drop in the diodes, the less work the regulator does, right? It's only there since I read 18.9V with no load 🙂
Koda, as an aside, there are now also alternative methods that use cheap small ebay step-up switchmode modules where the output can be set to a regulated level such as 12V, as long as the input is lower than about 10Vdc. They also work pretty neatly for preamp 12.6Vdc valve heater powering from a spare 5Vac winding just as much as a 6.3V winding.
AC heating in a phono preamp is a BAD idea. Yes, it is possible to obtain acceptable residual hum levels in AC heated phono circuitry, but the amount of discomfort (as in royal PITA) involved makes (IMO) the choice of DC heating a total "no brainer".
I always found any hum in my valve equipment was more due to bad layout, long wires on inputs and poor screening of input. Locating transformers near input is bad too. High volts ac nears signals. Poor pcb design too.
Well, I did design this to run a relay module from a heater winding 🙂 18.9V (unloaded, pre-regulator) would blow it up.
I agree with Eli about DC for phono, or any other small tubes for that matter. I use 12V SMPS for my heaters. That's why the headphone board I made has a 12V input for heaters even though they have 6V heaters 🙂 Even when I'm using a linear supply, I still make it 12V.
I've also built a cheap test amp using the chassis as signal ground, power ground, house ground, and AC heater return (one heater wire per tube socket, the AC return to chassis) and no hum there either. It was a cheap push pull amp though, not a phono stage.
I agree with Eli about DC for phono, or any other small tubes for that matter. I use 12V SMPS for my heaters. That's why the headphone board I made has a 12V input for heaters even though they have 6V heaters 🙂 Even when I'm using a linear supply, I still make it 12V.
I've also built a cheap test amp using the chassis as signal ground, power ground, house ground, and AC heater return (one heater wire per tube socket, the AC return to chassis) and no hum there either. It was a cheap push pull amp though, not a phono stage.
@kodabmx
Thank you for mentioning the MIC29300. Some quick computations suggest that Schottky Diode voltage doubling 5 VAC yields enough headroom for the 12 V. version of that low dropout (LDO) part to function reliably.
Does the MIC29300 have a negative counterpart, as is the case with 7812/7912?
Thank you for mentioning the MIC29300. Some quick computations suggest that Schottky Diode voltage doubling 5 VAC yields enough headroom for the 12 V. version of that low dropout (LDO) part to function reliably.
Does the MIC29300 have a negative counterpart, as is the case with 7812/7912?
Does the current remain the same? I guess not. It will be halved from the 6.3V.
Example.
If for 6.3V we have 2A, for 12V there will be less, 1A.
Correct. Nothing is free 🙂
Depending on how much current the load needs, C3 might be omitted.
It's definitely a near thing, but it seems a LM2990T would work with Schottky voltage doubled 5 VAC in 300 mA. 12 VDC heater supply.
