DC Filament power supply - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

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
Reply
 
Thread Tools Search this Thread
Old 17th September 2002, 09:15 PM   #11
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Thumbs up AC DC

Well done Dhaen!
This is a little known secret.
Indeed the AC's alternating behaviour prevents notching.
It has sort of a cleaning effect preventing heater and cathode to stick together.
Notching occurs most often at the top of the inverted V filament,which seems logical to me since that's where it is closest to the cathode.
Some special winding of the heaters (such as in the 300B) was especially developped to heat the cathode as evenly as possible.
Other constructions exist,just to say that the heater to cathode relationship is VERY important to the end result you can expect from a tube.
Most change their characterics completely when changing parameters here.(current starvation over- and undervoltage etc.)
Those of you having the gear to do plots can eat their heart out experimenting with this.
I'm not familiar enough with those software programs such as Sofia,Pspice and such to say if they provide options to simulate this.



Rgds,
__________________
Frank
  Reply With Quote
Old 17th September 2002, 09:20 PM   #12
diyAudio Member
 
Gabevee's Avatar
 
Join Date: Feb 2002
Location: Richmond, VA.
I wonder if the reason is that the mean voltage for AC 6 volts is actually lower than a DC 6 volts? I skimmed over an article once about this but forgot much of it. I will look it over again in more detail. For 6 volt heaters, that is.

As for DHT, I have keenly been interested in this because of my antiques. With DC the emission tends to be higher from one end, as far as what I read is concerned. For DHT's using AC and center tapping the filament to ground connection (the bias resistor etc.) is ideal for even distribution of emission.

However, with the DC filaments I do not know if this is an issue. Perhaps the filament is specially designed for uneven emissions. I do not recall reading such.

Gabe
__________________
Gabe CGV Electronics
Home of the CGV-300B amplifier on a budget
  Reply With Quote
Old 17th September 2002, 09:42 PM   #13
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Default AC DC

Gabe,

You're right,but the difference is not great.In this case 6.3 VAC would amount to roughly 6VDC.

DHT:in fact if you use DC on a DHT ,such as the ones with especially irregular filament windings ,you will throw the whole design out of balance creating "hot spots" on the cathode.
Go for AC heating and trim the hum away with a rheostat and you're done.Simple.
Your tubes will love you for it.

Rgds,
__________________
Frank
  Reply With Quote
Old 17th September 2002, 10:11 PM   #14
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
Default Notching

Quote:
Originally posted by fdegrove
Well done Dhaen!
This is a little known secret.
Rgds,
Must be my Belgian name! (There should be an apostrophe).

Seriously, you're the first person I've come across who knows about notching
  Reply With Quote
Old 17th September 2002, 10:59 PM   #15
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Default ac dc

D'haen??

Thanks for returning the compliment.
Wait 'till I get upto speed!


Cheers,
__________________
Frank
  Reply With Quote
Old 17th September 2002, 11:01 PM   #16
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
Default D'haen

That's it.
  Reply With Quote
Old 17th September 2002, 11:47 PM   #17
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
theoretical and longevity issues aside heater circuits have direct effect on the sonics. in DHT the heater is directly in the signal path and even in indirectly heated valves the sonics change drastically depending on whether heating is ac/dc/regulated/filtered. quality of regulating circuits and capacitors is paramount. generally, ac sounds best to me on all valves. if hum is an issue, current sourced heating is second best.

peter
  Reply With Quote
Old 18th September 2002, 12:00 AM   #18
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Default AC DC

Fellows,

Quote:
heater circuits have direct effect on the sonics
I couldn't agree more.
Heating affects the characteristics (curves) hence operating points of the valve.
All manuals I know of show curves with the valve AC heated,you change that and you're off on the wrong track.
That's one more reason to do some curve plotting before you choose you're operating points!
Good thing these valves are good natured and usually abuse resistant...

Rgds,
__________________
Frank
  Reply With Quote
Old 18th September 2002, 07:29 AM   #19
SHiFTY is offline SHiFTY  New Zealand
diyAudio Member
 
SHiFTY's Avatar
 
Join Date: Jul 2002
Location: New Zealand
Make sure your transformer can handle it tho, using DC will probably require 30-40% more current, and there will be enormous inrush current to fill the big reservoir caps you will need...

Go AC, its easier for power tubes!

I run my PP amp with all AC filaments except the very first preamp section and its dead quiet, no hum at all.

The best way to get rid of hum IMHO is to separate your grounds- run all signal and speaker grounds to one point, all cathodes to another, all power supply to yet another, and join them all at only one point. I call it multiple star grounding

It fixed the hum in my amp!
  Reply With Quote
Old 18th September 2002, 12:16 PM   #20
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Thumbs up AC DC

Shifty,

Yes,that's how stargrounding is meant to be done.
And of course having a scope at hand to decide exactly where to ground surely helps.

Rgds,
__________________
Frank
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Yet another DHT filament supply astouffer Tubes / Valves 25 6th July 2009 12:08 AM
filament power supply question Captn Dave Tubes / Valves 6 13th December 2008 02:30 AM
Parallel vs. series filament supply - or another filament idea engels Tubes / Valves 11 13th May 2007 02:06 PM
Switching power supply & filament Aiace Tubes / Valves 2 29th June 2004 01:18 AM
When using a DC filament supply on a DHT... Saurav Tubes / Valves 31 18th September 2003 06:03 AM


New To Site? Need Help?

All times are GMT. The time now is 02:53 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2