heater wiring - the Good the Bad and the Ugly

[wiredwithtubes]

Originally Posted by DF96

Could be a sign of spurious RF oscillation getting propagated along the heater wiring, rather than normal hum.

Not RF, looked at it on a scope. I first tried a 100 ohm balance pot and it worked but still had a little residual hum, using the caps no hum. I also tried connecting the caps with clip leads across different tubes and the result was the same. If it was some spurious pickup the results would have varied moving the clip leads around. Perhaps someone else can try it and see if they get the same results. I first used Illinois Capacitor coupling capacitors and the results were the same, I only went to ceramic caps because they are physically smaller.

[gaborbela]

Originally Posted by wiredwithtubes

I've found that on filament windings with no center tap bypassing both sides of the filament line with caps works better to eliminate hum than a balance pot. I used .47uf @ 100V ceramic caps.

Hello
Thank you very much.
Great idea, I hope these work for the higher power GU50 to.. That is 12.6V but I must have to check the tube data.
I have 12.5V DC also. Is not better if I use DC for the GU50.
Again I have to take a look at the tube data what is the recommendation. Great help, thanks one more time.
Greetings Gabor

[gillougillou]

Looking for somebody who have AC heater with 300B and NO noise.
It could be possible as WE91 is ac ?

Thanks for your help.

Gilles.

[valve5425]

Hi Gilles.

I'm getting 3.9mv and 2.9mv 100hz respectively at the terminals of my AC supplied JELabs 300B monoblocks. Nothing fancy here, just AC straight to a wirewound dropping resistor, routed around the outside and with a hum pot. I haven't tweaked it for optimum performance, just made sure the wires were twisted and placed to the outer edge of the chassis. Would be interesting to see what other folks are achieving and what measurement would be considered "No noise". (Now I've measured it I'm going to have to find out why I've got 1 mv difference. Damn!!)

[rongon]

To echo valve5425's question, and out of my own curiosity, would 4mV of AC hum on the filaments of a 2A3 or 300B be considered objectionable?
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[rongon]

Originally Posted by wiredwithtubes

I've found that on filament windings with no center tap bypassing both sides of the filament line with caps works better to eliminate hum than a balance pot. I used .47uf @ 100V ceramic caps.

If you wanted to use cathode bias on a DHT, but still use those .47uF bypassing caps for the filaments, where would you put the cathode bias resistor?

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[Goodlagger]

Any thoughts

[roline]

Elevated twisted pair...

[wiredwithtubes]

Originally Posted by rongon

If you wanted to use cathode bias on a DHT, but still use those .47uF bypassing caps for the filaments, where would you put the cathode bias resistor?

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I should think you would just connect the resistor from filament to ground. But then the .47 caps would act like a bypass and boost at very high frequencies. I'm only familiar with DHT power output tubes and on a power tube you would want a decent value bypass cap. Might be best to use a separate filament transformer in such a case.