Common Mode Chokes for Heater Supplies

[ppereira]

http://cgi.ebay.com/AlfaMag-Talema-...QitemZ3876395780QQcategoryZ7288QQcmdZViewItem

I bought a pack of these on eBay recently with the intention of using them for filtering 6B4G's heater supply. Wondering if anyone else has tried this and what the results are before turning on the soldering iron....

BTW the seller's website at www.alfamag.com with many other choices.

(I am not affiliated with Alfamag in any way...)

 

[leadbelly]

Sorry to break the bad news to you, but you will get negligable PS filtering from those. They are rated at 0.1 mH. In the tube amp world we use chokes greater than 1 H in value, 4 orders of magnitude higher (albeit those are usually in the HT supply).

 

[poobah]

Leadbelly,

I think he's talking about using those to choke out common mode rf trash on his AC powered heaters... not for filtering DC heater current.

 

[ppereira]

That's right 6B4G heater's rated at 6.3V 1A.

 

[leadbelly]

I think he's talking about using those to choke out common mode rf trash on his AC powered heaters... not for filtering DC heater current.

Thanks. I'll shut up now.

 

[EC8010]

To answer the original question: It all depends. I knew you'd find that useful. Seriously, it depends on how much of an RF problem you have in the first place. The worst scenario would be that you have a single toroidal mains transformer that feeds silicon HT rectifiers and the heater supplies. The best would be that you have a dedicated EI transformer for the heaters and it is either a dual bobbin design or has a foil electrostatic screen. In the "best" scenario, there's little improvement left to be gained, in the "worst," CM chokes could make a big difference. The difference is similar to the difference between the sound during the day and after midnight (when the mains is quieter).

 

[ppereira]

Thanks, that helps. My scenario is somewhat in the middle of those extremes: It's an EI transformer but no shield with secondaries for B+ and heaters. I guess I'll give it a try and see what happens.

Unrelated to the original topic, the topology of this project is still changing. Right now I have a Jensen 10k:10k input transformer feeding a C3G triode connected. The C3G is interstage connected (LL1660 in SE to PP) to the 6B4G output stage. The 6B4G's are cathode biased using a common cathode resistor with James 30W PP transformer to complete the chain. B+ is regulated and heater supplies are DC unregulated but well filtered. As is the amplifier is very quiet.

On a scope the story is different: a 1KHZ square wave shows massive ringing and a 10KHZ sinewave looks more like a really bad sinewave . The Jensen looks like clean on the scope. The LL1660 starts to ring and the output transfomer really finishes the job... I understand that music is not square waves but I still would like to see a much cleaner square wave. Does anyone have any insight on how to damp the interstage and output transformer to get rid of some of this ringing?

Thanks again

 

[Fuling]

Put resistors across the interstage secondaries to load it down a bit.