• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
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Can all tubes be heated with DC?

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Can all tubes be heated with DC? I'm wondering because I have a set of ECC99 (almost same as E182CC) and I can heat them with AC but when I try to apply 6.3VDC to the heaters nothing happens. I measure the filament pins (4 and 5) and I read about 0.09V..

This tube is a dual triode with two filament pins and a filament common (pin 9). I tried applying DC to pins 4 and 5 and to pins 4 (or 5) and 9.

I'm using an LM317 to produce 6.3VDC.

Any ideas?

Thanks
 
diyAudio Senior Member
Joined 2002
I FORGOT....

Hi,

BTW, the voltage regulator likes to see at least 5V more at the input than it's output.

If it doesn't it's not going to regulate properly.

So your heater winding is going to be around 8 VAC 1A for this ECC 99 or 15VAC 0.5A if you chouse to heat it at 12.6V.

Hope that helps,;)
 
HeadSh0T said:
I'm using an LM317 to produce 6.3VDC.
Sounds like your LM317 is going into current limit. Light globes have about seven times greater resistance when at running temperature than when cold. I expect tube heaters / filaments would too; perhaps not quitre as great a difference because of lower running tmperature. This means they need lots more starting current than running current. Raise the reg voltage to 12.6 volts and do like Bas suggests and apply this to pins 4&5. Leave 9 disconnected. This will halve the starting as well as running current. Dropout voltage of an LM317 is about 2 volts depending on the current so really you would want 16-20 volts going into it. If you really wanted to get fancy you could give the tube filament a soft start to lower the inrush current even more by having a slowly rising voltage on the adj pin of the LM317. An app note somewhere would cover this.
 
Ex-Moderator
Joined 2003
Depending on how much current you need, you might want to change to a 338 (same package, pinout, and surrounding circuitry). As Circlotron says, the cold resistance of a valve is much lower than the hot, and this can sometimes cause reglators to go into current limit. The Linear Technology data sheets for both devices gives current limit details graphically.
 
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