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Please help to lower ac heather voltage

post #1 of 5
6/27/11 at 6:28pm
Thread Starter 

Hi

Just upgraded transformers in Bijou and now e88cc and ecc99 have 7.4vac on heaters and ez81 has 7.1vac. would adding 1-2 ohm 10w resistors lower the voltage?

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post #2 of 5
6/27/11 at 6:53pm

 

Quote:
Originally Posted by MrClean View Post

Hi

Just upgraded transformers in Bijou and now e88cc and ecc99 have 7.4vac on heaters and ez81 has 7.1vac. would adding 1-2 ohm 10w resistors lower the voltage?


yepp. 

 

use ohms law:

V/I=R

Where 

V=the voltage you want to drop in VOLTS

I=the current through the tubes in AMPS(take note of whats in series and whats in parallel)

R=resisor, ohms if you got the units right. probably between 1 and 2 ohms. 

 

easy!

 

There is a nifty calculator I use here:

 

http://www.sengpielaudio.com/calculator-ohm.htm

that does all the math when you load in 2 values. 

Be sure to add a healthy safety factor, 3 to 4 times the power the calculator says should not be too hard. 

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post #3 of 5
6/27/11 at 7:39pm
Quote:
Originally Posted by MrClean View Post

Hi

Just upgraded transformers in Bijou and now e88cc and ecc99 have 7.4vac on heaters and ez81 has 7.1vac. would adding 1-2 ohm 10w resistors lower the voltage?



Depending on your transformer, probably more like .47 ohm to 1 ohm.

 

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post #4 of 5
7/2/11 at 8:48pm
Thread Starter 

Thank you for help, I ended up adding 0.47ohm 5w resistors on each heater wire and now tubes are running between 5.8vac and 6.4vac,

ended up mounting resistors on heat sinks since they were getting warm.

It's strange but I can swear that amplifier sounds better.

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post #5 of 5
7/2/11 at 10:30pm

Good to hear everything is running nice :)

 

Dont touch resistors. It is acceptable for a high power resistor to run hot enough to burn skin, and on occasion the insulation around the resistor will fail (if they are in a high voltage app) possibly shocking the user. If nothing else it requires putting your hands WAY closer to the insides of a running tube amp than anyone should be comfy with. 

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