
Home  Forums  Rules  Articles  diyAudio Store  Gallery  Wiki  Blogs  Register  Donations  FAQ  Calendar  Search  Today's Posts  Mark Forums Read  Search 
Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum 

Please consider donating to help us continue to serve you.
Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving 

Thread Tools  Search this Thread 
12th December 2008, 09:07 PM  #1 
diyAudio Member
Join Date: Jun 2008

filament power supply question
Gentlemen,
I'm trying to slap together a DC filament power supply from junk drawer items and questionable bits of knowledge. I have a few boneheaded noob questions: Here's the deal. I have a 14 watt wall wart transformer together with a bridge rectifier and a 22 uf cap followed by about 60 ohms of resistance and another 200uf of capacitance for the 12.6 volts I need. I still have a quarter volt of ripple. So I suppose I should substitute a choke for the resistance, right? I pulled a small dime sized toroidal inductor (I think thats what it is, it lookes like a copper wire minidoughnut) from a old circuit card and put it in the circuit to absolutely no effect. The impedance is only 1.8 ohms! Is it fair to use the formula for inductive reactance to back out the inductance? If so it's 1.8/(2*pi*120) or .0024 Henries. Can that be correct? I know I need about 3 Henries. I don't get it, what value would such a small inductor have in any circiut? For that matter, is this thing even an inductor? Thanks 
12th December 2008, 11:29 PM  #2 
diyAudio Moderator

You're probably saturating the poor thing. To be effective at that low frequency and that high current, you'll need a core the size of a softball at the least to get an effective 3 henry inductor.
__________________
"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is." 
13th December 2008, 12:13 AM  #3 
diyAudio Member
Join Date: Jun 2008

Yup. I get it now. PSUD2 and the Antique Electronic site clearly illustrate that my approach is not practical due to the size and cost of the inductor due to the current requirements. I'll need to use a regulated supply. A good lab experiment though.
The low voltage regulator kit from GlassWare looks like a real bargan. I think that is the ticket. 
13th December 2008, 12:23 AM  #4 
diyAudio Member
Join Date: Jun 2008
Location: SoCal

Load resistance divided by 1200 will get you the Henries needed for a particular circuit. If you know the load resistance then you know the current, in fact you probably need to know the current to figure out the load resistance. Any way you figure out the different values this formula is real easy to remember and works pretty well.
Craig 
13th December 2008, 12:35 AM  #5 
diyAudio Member
Join Date: Jun 2008

Thanks craig. The load is a 6PN1  600ma at 6.3 volts. That should be 10.5 ohms. Using your formula that is only 0.005 henries. Is that correct?? PSU2 is not too happy with it.

13th December 2008, 01:00 AM  #6 
diyAudio Member
Join Date: Jun 2008
Location: SoCal

To be honest with you I've only used that formula for high voltages, ie 400 @ 15 ma, which ends up being a 22 henry choke. It shouldn't make any difference though. Look at the chokes in solid state amps, they too are in the mH range. For your circuit I got almost 9mH. Try googling for other formulas and see what you get, there are many out there. My friend is a transformer engineer, he came up with the same figure I did for my 22 Henry choke but used a different method. There are more ways to skin a cat but the cat always ends up skinned.
Craig 
13th December 2008, 01:30 AM  #7 
diyAudio Member
Join Date: Jun 2008
Location: SoCal

Check out Hagerman Technology, using that formula I got 9.3mH. There you fill in blanks so not sure what formula is. But the cat in still nekked!
Craig 
Thread Tools  Search this Thread 


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Tuner filament supply question  rdf  Tubes / Valves  3  6th August 2007 06:48 AM 
Parallel vs. series filament supply  or another filament idea  engels  Tubes / Valves  11  13th May 2007 01:06 PM 
DC filament supply LC or CL  TBM  Tubes / Valves  1  7th August 2005 07:26 PM 
Switching power supply & filament  Aiace  Tubes / Valves  2  29th June 2004 12:18 AM 
DC Filament power supply  oldstyle  Tubes / Valves  26  2nd November 2002 01:26 PM 
New To Site?  Need Help? 