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DC Filament supply boards

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filreg_pcb_small.jpg

I've had a number of people ask me to make the DC filament supply boards I made for an earlier project available. I've finally gotten around to it...

Regulated DC filament supply

I made the PCB the same size/shape/mounting as the Tentlabs supply, so you can try this one (constant voltage) and replace it with the Tentlabs voltage-controlled-constant-current supply without any modifications to your amp.

Pete
 
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I've had a number of people ask me to make the DC filament supply boards I made for an earlier project available. I've finally gotten around to it...


I'm wanting to do something like this myself. One question. You say the CML drops some voltage. Why not have the regulator sample the voltage at the output terminals so as to compensate for the (load dependent) voltage drop. (Yes I know the heater load stays constant but some of use swap tubes around.) The cost and BOM remains unchanged.

Maybe there is a problem with this? Oscillation maybe?

In the past I've built power supplies for remote loads that had 50 or 150 feet of cable between the supply and load. I'd run one small gauge wire in the cable to sense the voltage at the load end of the cable so as to automatically account for voltage drop in the cable. Seems to me the inductor is exactly like a long power cable, only rolled up.
 
Maybe there is a problem with this? Oscillation maybe?

Yup. If not oscillation, at least some AC response issues. One of my mantras is that if you want to use a regulated power supply in audio, make darn sure it does no harm. To me, that means the AC response has to be carefully controlled.

IMO, that's why shunt regulators tend to work well in audio. Less likely to get in the signal path (not that they do not or cannot...)

Taking the feedback after the CML could result in some AC response anomolies that might not sound so good...

Pete
 
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ChrisA, sounds as if you may have been fortunate not to get oscillation with your long run. (Or may be just well designed ;) ). I know that extending the negative leg (after / under the resistor) to the load can work well, but that does not normally apply to the upper / feedback arm.


Taking the feedback after the CML could result in some AC response anomolies that might not sound so good...

Too right Pete. Experience suggests that the only thing that should go in the feedback loop of a three terminal regulator is a resistor, and that it should sit right next to the regulator.


Nice board Pete, thanks for posting that; I am sure it will be very useful to many of us.
 
ChrisA, sounds as if you may have been fortunate not to get oscillation with your long run. (Or may be just well designed ;) ). I know that extending the negative leg (after / under the resistor) to the load can work well, but that does not normally apply to the upper / feedback arm.

We were supping power, a handful of amps, to a thermoelectric cooling system. Bundled in the cable also was water tubing for the heat sink. If the load is not reactive and has a time constant of several seconds not much can happen. I think the "sense wire" was connected to a voltage divider that was in parallel to the load. You can do it. It's a pretty common technique.
 
I'm working on a new design for an ultrasonic filament supply... it will take a little time, but it looks promising.

Shooting for 2 x 2.5A at 125kHz, transformer isolated sine wave, in the same form factor as these boards.

Stay tuned!

Pete

Half bridge LLC or LCC, variable or fixed frequency?
Or just plain single switch ZVS?
The main question is what is the feedthrough capacitance between the windings?
I've got as low as 13pF @ 80W
Alex
 
CQ CQ Pete are you Monitoring?

Hello,
Today I received the parts to assemble 2 of the PCB’s. Is there a need or strong recommendation to isolate the LM 1084 from the heatsink. Or is it just fine to apply some thermal goop and directly attach the IC’s to the heatsink?
DT
All just for fun!
 
Hello,
I received the parts from Mouser a week and some ago and assembled the PCB’ this morning. They heat up nice with a dummy resistor. Wow the assembly went quickly. The time saved is well worth the price of the PCB’s over the time used for point to point construction.
I go slowly. I will report back on the performance in the DHT circuit.
DT
All just for fun!
 
I read through the link and can't figure out if these would be good to 20v 3a for heating GM70 tubes. In one line it says "for 1.25v to -25v and 5a" Is that really a negative sign? or will they power up my GM70 tubes?

Hello,
I do not want to speak out of school. My view of this regulator is that it is an updated low drop out version of the lm 317 variable regulator. Good, in terms of volts, up to the upper limit of the LT1084. The common mode choke is limited to 3.something amps. I do not know how many watts the heat sink is good for.
How is that custom Halloween amplifier you are building?
DT
All just for fun!
 
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