DHT output tubes and DC heating

[jarthel]

Can I:

1. connect their heaters in parallel?
2. same as no. 1 but in series
3. I guess that if nos. 1 and 2 aren't possible, does that mean I must have a separate winding for each tube?

Thank you very much

[i_should_coco]

Is this SE or PP? Output tubes or...?

For SE, you will need a separate winding for each channel and each stage.

For PP it is ok to parallel up the heaters of the tubes in a PP pair.

[tubelab.com]

1. connect their heaters in parallel?

This is possible. You can connect the heaters in parallel even in a SE amp, if one side of the heaters is grounded. This requires fixed bias, and some other means to monitor plate current. I use a 10 ohm resistor in series with the plate. I use one filament winding, rectifier, filter, and regulator chip to power both channels.

It is also possible on a push pull amp if both tubes share a common cathode resistor. A seperate winding for each channel would be required.

I have seen (in a name brand amp) one filament winding powering the heaters in both channels of a SE amp. The two channels shared a common cathode resistor and relied on a big electrolytic bypass cap for channel separation. Not what I would call optimum.

Wiring the two heaters in series would guarantee a different bias level for each tube. This could be compensated for with fixed bias, but again not optimum.

[andyjevans]

One thing to bear in mind is whether you are likely to pull one tube out when you run two tubes off one DC supply. If you do then you will find the following:

2 tubes in series, voltage regulation - OK - remaining tube does not light since circuit is broken

2 tubes in parallel, voltage regulation - OK - remaining tube gets same voltage

2 tubes in series, current regulation - OK - remaining tube does not light since circuit is broken

2 tubes in parallel, current regulation - NO!!! - remaining tube gets double the current!

[jarthel]

so what is the recommended solution?

separate heaters for each output tubes?

for example in push-pull: Can I construct 2x DC supply out 1 secondary for each channel? Is this okay?

Thanks again