Valvecaster 'dunno'...what's the high voltage limit for LM317 input?

[petemoore]

  18v supply for circuit, WW feeds LM317, output is about 18vdc.
  I thought of using a 30vdc WW which puts out 38v.
  I used a 265ohm for R1, and a 4.85k for R2, the regulator is dropping only a small voltage.
  The RS chips package schematic shows '28v' by the input...
  What is the highest voltage you've gotten away with putting into an LM317 ?
   7812 for the heater.
  12au7a must have been shoddy because the 12at7 sounds a little better.
  Still it sounds kinda neat on single notes but a bit ragged...

[Ripthorn]

Depends on the kind of 317.  I have put full blown phantom power through 317's (48V) but the ones I got were rated to 60V input.  You should check your specific kind.

[petemoore]

  Says 37V output...that means 39V input I guess...
  http://www.radioshack.com/product/index.jsp?productId=2062601&tab=features
  LM317T

[petemoore]

  I put the 37VDC on the circuit. With the tube I have, 12at7, there is marked improvement in it's ability to handle higher input levels without breaking up obtrusively.
  The LM317 is literally running cool, it's hard to tell it's doing anything.
  It is sounding great also, nothing at all like my TS or BMP or FF or any combination of boosters into or out of them, doesn't exactly sound like my tube amp either, I was hitting the VC with the Blackfinger output...but mahn that is a fun play with that tone, easy to get a grungy breakover.
  Tubes are about to start taking over my pedalboard, the FF and BMP aren't going anywhere, it looks like the TS and that other booster are going to on to take a break.
  Only problem isn't a burnt 7812, but the heat sink isn't big enough either...close, but running hotter than I'd like after a few minutes.
  Edit: I just added a bunch of copper heatsink, the thermal dissipation isn't keeping up very well, too hot to touch the sink after 4minutes.
  I'm glad someone suggested I should have one, thank you !
  ...who was that, FC I think.
  And Matsumin and everyone else involved and showing interest in anything to do with Valvecaster, which includes everyone.
  Yes, I still have work to do on it, I'll have to figure out some kind of workaround, perhaps there's a way to dissipate the heat and not the voltage into the box?, or use yet another lm317 to 'pre-drop' some of the voltage? 
  or...I'm open for suggestions !
   

[petemoore]

  I finally read the data sheet again.
  Shows that the tab is connected to the ground pin...
  A screw helps dissipate heat into that side of the box and a wire helps carry it to the other side of the box through the sleeve connection of the output jack !
  Amazing how much heat one little chip can put out !

[GibsonGM]

Isn't it??  I used a 2N3055 as a DC amplifier to control a train light set (a dimmer, really)...that thing would get up to almost 200F when set on the dimmest setting (most dissipating).  Insane!  And only on 12VDC.

I was going to use a 7812 on my heaters, but the McTube doesn't put out enough at the rectifier to 'activate it', I don't think. I got crappy voltages (high??), so went back to the string o' diodes technique.   

[Sir H C]

Look at switching regulators, those can buck down the voltage with little heat. 

[R.G.]

OK, you guys have read stuff here before. What's the first thing you should think when you wonder "What is the (limit) for a (device)?"

That's right - google "(device) datasheet". In this case, the first entry is the Nation page for the LM317, which tells us 40V.

However...
The LM317 is somewhat unique in that it can work in a floating mode as well. The National Semi app note on it shows how to make it regulate hundreds of volts by using a high voltage device to shield it from incoming high voltages.

[earthtonesaudio]

There's also the small detail of the voltage difference between input and output.  Big difference=big heat.

[petemoore]

  The LM317 runs cool at ~38v. Very little warming, no heat sink.
  I tried to get close to the 240ohm and 5k shown on the package/schematic, for regulation w/minimum V drop.
  OTOH..the 7812, doing a 38v to 12v drop, is a super heater chip. Heat sinking involved attachment to the box on two sides, it still gets 'pretty hot' but I can touch the heatsink for 5 seconds, and the sink seems to cycle...the first three minutes after start up it seems to get the hottest, after 5 minutes noticably cooler, or seems to be, perhaps the current is reduced as the filaments warm up ?...no matter...the box is working great.