I've never been able to get my 6SN7/6SN7 Aikido with AC heaters completely noise free until I elevated the heater above ground. I soldered in two 100 ohm resistors from CT to each leg and with a voltage divider from a filtered B+ supply I injected about 28 volts DC into the CT. The noise I had enjoyed as I placed my ear next to the speaker was now gone.
A video I had watched on you tube said to have the R2 value less than 100k. I'd never heard of having to stay below 100K before. Mine is roughly 1/2 of that with R1 being 440K. So I'm looking at about 27-28VDC from the divider. So, am I good with respect to what the 6SN7 can tolerate?
I know what I put together isn't precise but I went with the parts I happened to have in my junk box. I am uncertain as to what the elevated voltage should be on the Aikido.
A video I had watched on you tube said to have the R2 value less than 100k. I'd never heard of having to stay below 100K before. Mine is roughly 1/2 of that with R1 being 440K. So I'm looking at about 27-28VDC from the divider. So, am I good with respect to what the 6SN7 can tolerate?
I know what I put together isn't precise but I went with the parts I happened to have in my junk box. I am uncertain as to what the elevated voltage should be on the Aikido.
The specs for the 6SN7 say that the heater/cathode voltage is 100V, so you're good to go. If the noise is gone, then you're done.
Thank you for your response. I just wanted to make sure my voltage divider was correct. I'm noise free now.
Burnedfingers, can you clarify your elevated circuit please. Does your heater winding have a CT, or are you using CT to describe the mid-point node made by two 100 ohm resistors connected across your heater winding?
Are you using a resistor divider to provide the 28Vdc - are the resistors in that divider being called R1 and R2 ? Have you capacitor decoupled the 28Vdc node?
What DC voltage does your top 6SN7 cathode sit at ?
Are you using a resistor divider to provide the 28Vdc - are the resistors in that divider being called R1 and R2 ? Have you capacitor decoupled the 28Vdc node?
What DC voltage does your top 6SN7 cathode sit at ?
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I should have mentioned I got rid of the two 100 ohm resistors and took the 27vdc directly to the transformer center tap.
I have designed numerous valve amplifiers and mixers etc
Any hum I have had as yet has never been due to AC heaters.
Any hum I have had as yet has never been due to AC heaters.
Perhaps more prevalent with vintage valves, and age, the (typically very high) heater-cathode resistance can reduce over time and introduce a hum current in to cathode circuitry. The Aikido circuit in post #6 does not use cathode bias resistor bypassing, and hence makes that circuit more prone to hum ingress via the heater.
All I can say is with AC heaters on the Aikido 6SN7/6SN7 I have hum. Injecting DC into the center tap eliminates the hum. I went into the garage last night and removed the DC from the center tap and the hum came back and when I soldered back to the center tap the hum went away.
All my 6SN7's are very vintage age. I even checked them on the tube tester selecting tubes with matched sections.