is 330ohms enough load for 7812 output ?

Started by petemoore, January 17, 2009, 02:54:48 PM

Previous topic - Next topic

petemoore

  330ohms is what I measure the R of the heater filament of 12ax7.
  I can't seem to get but 2 volts or so out of these voltage regulator circuits.
  15.5Vdc across pins 1 and 3.
  Filament across pins 2 and 3.
  Seems simple but isn't.
 
Convention creates following, following creates convention.

The Tone God

Are you trying to simulate a tube heater load ? If you want to simulate 150mA you need a 80ohms 2W load or for 300mA you need a 40ohms 4W load.

You are reading the value with a cold heater. Remember that as the heater warms up the value will change. I would add some extra current for the cold start up to be safe.

Andrew

Jered

  Need more info. What your saying is confusing (could just be me) You've got 15 vdc to pin 1 and 3. Yet your reading 2 vdc? Pin 2 is ground. Where are you reading your voltage?
  15 vdc to pin 1, ground pin 2, and you should get 12 vdc at pin 3.
  For 12XXX7 tubes, 12 volts to pin 4, ground pin 5, or the opposite. Leave pin 9 floating.

puretube

Y`re measuring V-out minus V-in?  that sounds like 2V or a little more...

but what you want to know is V-in versus ground (>12V + 2V)
and V-out versus ground (=12V).
If it`s like that, than it`s OK.

petemoore

#4
  Measuring with everything connected.
  V+ to Gnd. [pin 1 and 3] =15.5vdc.
  Output to Gnd. [pin 2 to pin 3] =2v
  There is no 'ground' because the only thing connected to pin 3 is - of the floating DC output and one side of the heater [tube pin 4].
   
    but what you want to know is V-in versus ground (>12V + 2V)
  What's V- ? new on on this thread...
  and V-out versus ground (=12V). I wish...
If it`s like that, than it`s OK.
  The way I have it:
  Voltage regulator 7812 [negative Gnd. regulator]
  Pin 1 gets V+ which is 15.5v higher than 'Gnd.' this voltage is floating, pin 3
  Pin 3 and 2 have the heater filament across them.
  "Gnd." isn't really grounded, but is the negative side of the 15.5vdc supply voltage for the Vreg input.
   That's it...according to the package [which doesn't say much else, nothing about minimum load or anything] it should work.
 
Convention creates following, following creates convention.

petemoore

  When reading the pinout, I read with legs down print on IC facing me...
  1 input
  2 output
  3 Gnd.
Convention creates following, following creates convention.

kurtlives

My DIY site:
www.pdfelectronics.com

petemoore

#7
  Damned if the fine print is'nt gettin' me...
  Yes, when close in light is used it indeed looks to be the case.
  123 isnt always linear Pete...gotta read, even if it means getting the light right or getting out the mag-glass  !!
  Now maybe I've blown both regulators, back to the drawing board anyway, connecting it 'the other way' according to the data sheet code [fine print got me the first two times around] produces 0.0vdc at the regulator outputs, with what figures to be an input voltage of around 24v x 1.414, minus the diode drops.
 
Convention creates following, following creates convention.

runmikeyrun

if you picked up the reg from Radio Shack i noticed that the package labeling is misleading- it's shown labeled:

1- vin
2- vout
3- gnd

but on the pic of the CHIP it's labeled

_____
|      |
|      |
-------
| | |
| | |
1  3 2

So maybe that's what's F-ing you up.  I know i did a double take when i saw it and was thinking that it was pretty misleading.
Bassist for Foul Spirits
Head tinkerer at Torch Effects
Instagram: @torcheffects

Likes: old motorcycles, old music
Dislikes: old women

petemoore

  Would have been just as easy to re-arrange the texts [input / output  / Gnd] and have the light, small, hard to read numbering be more readable [larger print, more ink], as well as linear 123 instead of 132 like you wouldn't expect.
  Of course then I wouldn't have had to go and buy 2 voltage regulators for the second time this week either. 
  Fortunately the store is right next to where I'm helping my buddy get moved in to, they had 5 ct. last week, 1 ct. this week.
  Suffice it to say I found it easy to be confused because I didn't read it well enough.
  After the first failure [let this be a lesson to anyone but me because I do this kind of stuff too often...read the directions more carefully a second time.
Convention creates following, following creates convention.