Home » Audio » Thermionic Emissions » Fiament choke and filter scheme???
Fiament choke and filter scheme??? [message #9752] Thu, 03 August 2006 10:49 Go to next message
Norris Wilson is currently offline  Norris Wilson
Messages: 361
Registered: May 2009
Grand Master
Hi everyone,

An uneducated question here.

I am looking for advice from people who have had some experience with filament choke and filtering schemes for an amplifier front end or phono-pre use.

I am looking for a good filtering scheme to reduce the ripple and to prevent negligible problems associated with such a filter.

My question is based on a single stage AC heated 6SL7 in the front end of a P-P monoblock amplifier. The filment would be supplied by a seprate transformer per stage.

Would it be best to use a LCLCRC filter in one leg of the filament supply, with small hash chokes of 250uH, 20uF film caps AEON, and a variable resistor of small value? Or, use an LCLC in a common mode scheme with above chokes and capacitors?

I am afraid that a large filter capacitor with a high ESR rating would cause some problems with high frequency noise and charging-timing issues.

Any comments, or opinions about filament schemes are most welcome.

Thanks

Norris Wilson

Re: Filament choke and filter scheme??? [message #9753 is a reply to message #9752] Thu, 03 August 2006 13:40 Go to previous messageGo to next message
Damir is currently offline  Damir
Messages: 1005
Registered: May 2009
Illuminati (2nd Degree)
My experience - in my PPP monoblocs both power tubes and a driver heaters are powered with 6,3V AC. With proper bias adjustment (PP cancelation) there`s no hum in the speakers I can hear - period.
It requires proper (star) grounding, and (twisted) heater wiring layout, of course. Preserve the same phase (heater wire) for both PP tubes pins 2, and another phase (wire) for both tubes pins 7 (assuming "normal" octal power tubes - 6L6, EL34, KT88..., but the principle is the same).
Easiest with different heater wire colors, for example - pink and yellow...
IMO - only if you can`t get low enough hum with AC (I doubt it ), try DC heating...IMO, IME, YMMV, and all of that...

Re: Filament choke and filter scheme??? [message #9757 is a reply to message #9753] Fri, 04 August 2006 10:33 Go to previous messageGo to next message
Norris Wilson is currently offline  Norris Wilson
Messages: 361
Registered: May 2009
Grand Master
Hi Damir,

I said this was an uneducated question, maybe a little silly too.

It came to my attention that I proposed a filter for DC components.

Do you have any suggestios that would filter an AC filament supply?
Possibly the use of hash chokes in both legs of the heater supply?

Any suggestions of the type of filter, or text reference would be most helpful.

Norris

Re: Filament choke and filter scheme??? [message #9758 is a reply to message #9757] Fri, 04 August 2006 11:09 Go to previous messageGo to next message
Damir is currently offline  Damir
Messages: 1005
Registered: May 2009
Illuminati (2nd Degree)
Hmm, I`ll probably use a separate filament PT with electrostatic shield between primary and secondary, and commercial mains filter before it. Then (for DC) Shottky bridge (diodes bypassed with caps), low value R, then CLC - for high-current supply. For lower current and IDHT, IC series voltage regulator.
For DHT, probably I`ll try voltage reg. + CCS, or so, but I didn`t try this so far.
There`re some examples in "Valve Amplifiers" by M. Jones...

Re: Filament choke and filter scheme??? [message #9759 is a reply to message #9758] Fri, 04 August 2006 13:59 Go to previous message
Norris Wilson is currently offline  Norris Wilson
Messages: 361
Registered: May 2009
Grand Master
OK,
Thanks Damir for your help. I will check into your suggestions.
Norris

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