best way to elevate heater?

[opamps suck]

greetings

i have two B+ lines, 630V & 320V and one 6V heater. i want to lift the 6V 100V above ground. does it matter if i use the 630V or the 320V B+? they share a common ground. can't see that it should matter and in the past i've never given it much thought, but what do you think? thanks in advance

berry

[Geek]

Doesn't matter which line. Just use a simple resistor divider.

[zanash]

I'm looking to do something similar but struggling to find any details. I'm assuming this has the effect of lowering the noise floor ?

[Geek]

Yes.

It is also mandnatory for tubes with an elevated cathode voltage, like pass regulators and top-tubes in totem pole designs, as it keeps the heater-cathode rating from being exceeded.

[zanash]

Are you going to pass the info .....or just leave me swinging ?

I would not be asking for more details if knew the answers !

Even a web page would help !

[andyjevans]

I can tell you what I do -
You have two resistors in series from HT to earth, and the junction is where you take the DC reference. If the HT is 300v I use approx 300K in total for the two resistors, i.e. 1K of resistance for every volt of HT. For 300k that's 0.3 watts so use minimum 1 watt resistors.
To calculate voltage out, start with the ratio of bottom resistor to top. If the top resistor is 250k and the bottom is 50k, then ratio = Rbottom/Rbottom+Rtop. In this case .17. Voltage out is HTxratio, so 300x.17 = 50v. You can get other voltages out by changing the ratio. I do this in Excel.
Then from the junction I take a 330 ohm resistor to each leg of the AC heaters, and from the same junction a cap rated higher than the HT (300+ volts) to earth. Cap size is as big as I can squeeze in - probably 22uF to 47uF or something like that

Hope this helps - seems to work.

[zanash]

Thanks .........thats clearer.

So your dispencing with the heater taps from the power tranny and running from the HT side ?

[andyjevans]

I don't quite know what you mean by this - of course the AC heaters run off the heater windings, either on the mains transformer or their own transformer. The voltage divider is only to reference the AC heaters to DC. You can't run the heaters off the HT!!! Is all this clear?

[SY]

Originally posted by zanash

So your dispencing with the heater taps from the power tranny and running from the HT side ?

No, he's using the HT to drive a voltage divider. A tap on the divider is used to bias up the heater taps at a set voltage above ground.

[zanash]

yes see what your getting at now