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Old 18th May 2012, 11:56 AM   #1
6J6 is offline 6J6  Australia
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Default Decoupling DC heater supply between valves..benefit?

Hi all,

Think of how you typically decouple preamp stages in a valve audio amp using RC networks set to an appropriate time constant.

Now if you were to apply that to the heater supplies of preamp valves, for each valve, do you think there would be any benefit sonic or other?

Never really thought of any mutual effects of heaters in a power feed chain, irrespective of how clean the DC feed is (regulated or not).

I haven't seen this concept used in any amp and think it would be fun to see if it could lower a noise floor, improve linearity, reduce crosstalk artifacts etc. Would cathode to heater capacitance have any bearing on the common supply?

I've discounted AC heaters even with balance pots as most preamps I think sound better with DC. Yep, controversial comment I know

Any thoughts or ideas?

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Old 18th May 2012, 12:15 PM   #2
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If the valves has filamentary cathode (direct heating), and they also acts a cathode, you may decouple them. If indirectly heated, I believe it isnīt needed.
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Old 18th May 2012, 01:53 PM   #3
6J6 is offline 6J6  Australia
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Hi Osvaldo,

DHT's would definately benefit the most from this idea, as obviously the heater/filament is also the cathode.

I was mainly referring to indirectly heated valves which I use for everything, and especially about heater to cathode capacitance interacting with the supply and other valves.

I think there is validity for both. Can't understand why I haven't seen it on any schematics..

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Old 18th May 2012, 02:16 PM   #4
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I believe definitively is not necessary to decouple them. At audio frequencies, capacitive coupling is small because of the low capacitance and low frequencies. So coupling is very very poor. And in case of high frequencies, at RF levels, it is normally no necessary to use DC at heaters.

But, no think implies that for security or simple pleasure you want to add decoupling, I donīt see any trouble.
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Old 18th May 2012, 02:49 PM   #5
DF96 is offline DF96  England
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Heater decoupling is used in communications receivers (AC heaters of course). Very unlikely to make any difference for audio, except possibly to inject noise into a signal ground.
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Old 18th May 2012, 03:07 PM   #6
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Quote:
Originally Posted by DF96 View Post
Heater decoupling is used in communications receivers (AC heaters of course). Very unlikely to make any difference for audio, except possibly to inject noise into a signal ground.
100% agree.
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Old 18th May 2012, 03:08 PM   #7
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I think it's probably best to provide a low AC impedance path from the heater supply to the star ground for common cathode amplifiers. Cathode followers may sometimes benefit from or even require separate heater supplies.
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Old 18th May 2012, 03:14 PM   #8
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Quote:
Originally Posted by Michael Koster View Post
I think it's probably best to provide a low AC impedance path from the heater supply to the star ground for common cathode amplifiers. Cathode followers may sometimes benefit from or even require separate heater supplies....
... because they are AF live and DC elevated from ground.
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Old 27th May 2012, 06:42 AM   #9
regal is offline regal  United States
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For tubes that oscillate like WE417 I found huge improvement by decoupling the heater pins, That heater wire is an antennae.
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Old 27th May 2012, 07:26 AM   #10
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Hi Regal, what values would you use to decouple?
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