Power supply schematic? please critique.

[mike_mccue]

Thank John,
I appreciate your opinion.

My concern with the LM317 is that I am not experienced working with small heat sensitive parts and small traces on hand made PCBs.
I really enjoy working with eyelet boards that I make on my workbench and working with larger easy to see stuff.

I take your opinion about the tube rectifier at face value and agree that your reasoning is correct.

best regards,
mike

[Merlinb]

My concern with the LM317 is that I am not experienced working with small heat sensitive parts and small traces on hand made PCBs.

The 317 would supply so little current that heat really isn't a problem- we're talking milliwatts.

[mike_mccue]

I am speaking of my solder and assembly skills.

I'm still open to using the LM317, I juts need to buy a few and attempt a build I guess.

best,
mike

[Merlinb]

I am speaking of my solder and assembly skills.

They're probably not as wimpy as you think, you have to try pretty hard to solder one to death! (Unlike MOSFETs. Stupid MOSFETs)

[mike_mccue]

so here's the $10,000 question:

Do you think I can spread the legs of one to accommodate a fit with a eyelet board made with garolite and keystone eyelets?

I imagine the minimum spacing for the eyelets is wider than the standard package meant for PCB thru hole mounting.

For the past month I've been imagining having to use a breadboard or something for the phantom power ortion of the power supply circuit... and I suppose looking for excuses to avoid doing so.

best regards,
mike

[Merlinb]

If you can't spread the legs then you could just bolt it to the chassis and use wires to run to-from the board. Nothing unusual about that.

[Steve Conner]

Sure you can, I've mounted lots of TO-220 devices to tag boards and the like. The legs bend quite a bit, and you can solder on bits of wire to extend them if they don't go far enough.

[mike_mccue]

Thanks very much to both for the continued help.

How about the heatsink? There was some mention above about an insulator?
When I order a few LM317AHV will I also need to order a few heatsinks as well as insulators?

Can some one take a last look at the most recent schematic *20a.gif to see if I got the Phantom power correct finally?

Thanks again,
mike

[Merlinb]

Can some one take a last look at the most recent schematic *20a.gif to see if I got the Phantom power correct finally?

I can't see any problems with it. Might want a fuse in the B+ though...

[mike_mccue]

On the center tap?

I'm off to read your Valve wizard site to see what you recommend.

Also, did I miss the idea that you previously stated that heat is not a problem... does that mean I don't need a heatsink?

Thanks,
mike

[tedmich]

Thanks very much to both for the continued help.

How about the heatsink? There was some mention above about an insulator?
When I order a few LM317AHV will I also need to order a few heatsinks as well as insulators?

Can some one take a last look at the most recent schematic *20a.gif to see if I got the Phantom power correct finally?

Thanks again,
mike

The Lm317 MAY run without a heatsink, it has thermal shutdown built in, but a small extruded Al one and a mica pad (both available at radioshack) is cheap insurance; with any current they can get very hot. Heres one I built into a copper pipe cap


notice 20 turn trimmer, I potted it up once I was sure it worked correctly.

[mike_mccue]

Thanks tecmich,

It's helpful to see how you did that without a PCB. The mica is the electrical insulator, but it transfers heat? I guess it's sized to the standardized "package"?

re: Merlin's comment about the fuse on the HV.

I've added two fuses to the High Voltage AC before the rectifier.

I read Merlin's page that suggested that you can determine the amperage by experimenting first hand. Is there a practical way to predict a useful lowest amperage value?

I imagine a 500vAC rating is a good idea for whatever I end up with. Yes, no?

Here's the latest tube-preamp-21a.gif schematic.

best regards,
mike

[tedmich]

Thanks tecmich,

It's helpful to see how you did that without a PCB. The mica is the electrical insulator, but it transfers heat? I guess it's sized to the standardized "package"?

yes!
IME fuses are usually std. 250v slo blo units at about 1.5 - 2x the amps the circuit is expected to see

[mike_mccue]

Thanks. I'm working up a parts order.

best regards,
mike

[Enzo]

Here is a part that works like an LM317 but will take up to 125v directly.

TL783. I noticed it doing exactly this job in a mixer power supply.

Mouser sells them for under $2.

http://focus.ti.com/lit/ds/symlink/tl783.pdf