Floating 12V heaters

[GainFreak]

Hi,

I floated my 12VDC heaters at ~90VDC because of the CF failure issue discussed previously in Tubes section. I have two 100 Ohm resistors from pins 4 and 5 connected together and then to the 90V point.
Isn't it better instead of using an artificial CT to connect all tubes' pins 9 together and connect them to the 90V?

[Enzo]

Let me nitpick. I would say you elevated the heaters. To me floating heaters means they are not referenced to ground at all, or to anything else.

What would be gained by connecting the tube hetaer mid points to the 90v instead of doing what you did?

Your 12VDC was isolated from everything? There is no center tap to DC, in my view. SInce all you are concerned with here is overing the heater to cathode voltage spec, it should be sufficient to connect just one end of the heater supply to +90. That one end of the heaters was then 102 and the other 90 with respect to chassis shouldn't matter.

[GainFreak]

I would say you elevated the heaters.

Yes, I elevated the heaters to 90V /voltage divider from +HT/. The heater supply secondary is not CT-ed and is isolated - it feeds the heaters and switching relays, no connections to chassis ground.

What would be gained by connecting the tube hetaer mid points to the 90v instead of doing what you did?

It works, but I wasn't quite sure because I've never elevated heaters before.

SInce all you are concerned with here is overing the heater to cathode voltage spec, it should be sufficient to connect just one end of the heater supply to +90. That one end of the heaters was then 102 and the other 90 with respect to chassis shouldn't matter.

It looks even easier that way. Heaters are still + 20-30V above specs but I guess it's better than the usual +90-100V as in most CF cases.