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oldstyle 16th September 2002 10:05 PM

DC Filament power supply
Hi, there

As a beginner of Tube amp, I have a generic question regarding filament power supply. Is it true that I can always replace the AC supply with DC to reduce the noise? I bought a kit online. It uses a rare tube 11ms6, which require 12v filament power. The original design is AC power, can I change it to DC?

Can I just simply use 12vDC adapter?

Thanks in advance

Colt45 16th September 2002 10:11 PM

you can use any DC supply as long as it meets the current req's.

personally, I think DC on the heaters is a waste of time.

oldstyle 16th September 2002 10:21 PM



Tom Bavis 17th September 2002 12:11 AM

With 4 - 11MS8s, you'll need 1.8 Amps at 11.6V. Probably won't make any difference in a low gain power amp like this. But if you have hum, and more power supply capacitance doesn't reduce it, it'a a possibility.

john 17th September 2002 11:40 AM

Try Regulating your DC... This will give stability and consistency to the tubes and a benefit of much lower tube noise level.

fdegrove 17th September 2002 12:09 PM


Try Regulating your DC... This will give stability and consistency to the tubes and a benefit of much lower tube noise level.

I'm sorry to say but done properly AC heating the power tubes is often to be prefered.
I fail to see how the tubes are going to "see" more stabilty and consistency by supplying DC to the heaters?
If you have hum coming from the heater supply,something is not layed out properly,or you may have a short between heater and cathode on one of the tubes.
Moreover the tubes will last longer when fed by AC.


phil 17th September 2002 05:18 PM

Listening to music which is sitting on top of a hum is not hifi.
DC heaters is a much better idea, use a regulator or a CCS.

fdegrove 17th September 2002 05:48 PM


I wasn't stopping anyone from doing so,was I?
Still,as I said, when executed correctly, AC heating IDH powertubes is no problem whatsoever.
Sure they mustn't be starved on current:use of a correct transformer rating should take care of that.
You should always provide for a reasonable upwards margin for heater consumption.(I usually go for 30% at least,it may cost more but I never skimp on transformers. )
A CSS?Unless you go for special heater types designed for a specific current consumption (regardless of voltage) it is not a wise idea to use a ccs for this.
In current audio tubes manufacturers design for voltages,not current on heaters.
Take a good look at the databooks and you will notice it will severely limit you in experimenting with so called "equivalents"
E.g.:6dj8,6922,7308 and so on.
DHT are trickier but can still be done.
Hum should be both measurably below the noise floor of the circuit and inaudible.
Have you considered the situation where you would have an amp with 10 and more output tubes each consuming a couple of Ampere to heat up ?
And you're missing an important factor:AC heating is simply better for the tubes involved.After all they were designed for it and the part about AC prolonging their lifespan may not be important to you but is definitely important to most of us??
:( :(


Gabevee 17th September 2002 07:17 PM


How do the heaters benefit from AC versus DC? With AC not only does the voltage reverse 60 times per second, but the heat fluctuates 120 times per second. Wouldn't constant heat be better than fluctuating heat?



dhaen 17th September 2002 08:00 PM

My 0.02 Euro's worth:

Generally filaments can last longer with AC than DC. If you look at the specifications given by some bulb manufacturers, they quote a shorter lifetime for DC. This is apparently due to a phenomenon called "notching". If you examine a bulb filament near the end of it's life, there are small notches near to one end (can't remember which end).
Whether this has any relevance to tube filaments, at their lower temperatures, I don't know.

From another angle:
With AC the average emission of each part of the filament is more even. So possibly the filament emission lasts longer.

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