Elevating heaters in separate channels together

[geezertron]

I'm playing around with a toy 3W SE amp that allows me lots of opportunity to experiment. I've cobbled together a couple of reasonable "spud" pre-amp ideas, but both incorporate cathode followers so the heaters need to be elevated to around 75V to be safe.

Assuming I ever build a stereo amp from this it's common sense to wire the heaters together for the two channels. But both tubes would be sharing the same resistor chain voltage tap to elevate the heaters.

Generally speaking is there a downside to this? I can't see what it would be off hand, but figured I'd better ask. Could the two channels somehow interfere?

 

[Ketje]

As long as the elevated voltage is well decoupled to ground i see no problem.
Mona

 

[MagicBus]

I was looking at J. Broskie's CCDA schematic. For the DC elevation voltage divider he uses two uper resistors, each one coming from each channel B+ and both joined at the lower resistor and the decoupling capacitor. What would be the purpose of this?

 

[Ketje]

If he had used only one the other would feel neglected :lol:
Mona

 

[MagicBus]

If he had used only one the other would feel neglected :lol:
Mona

 

[geezertron]

As long as the elevated voltage is well decoupled to ground i see no problem.
Mona

Plan on using a 2uF film cap for this, seems more than enough without doing the actual calculation.

 

[DF96]

Two resistors means that you still get some elevation if one channel loses its supply rail. I'm not sure that matters, though.

 

[smbrown]

If you have seperate B+ supplies for each channel, I always put the same divider on each so that the load on the PS is the same, but I only use one to go ahead and raise the heater. Similar to how Gordon Rankin did the PS for the Bugle.

 

[MagicBus]

Two resistors means that you still get some elevation if one channel loses its supply rail. I'm not sure that matters, though.

If you have seperate B+ supplies for each channel, I always put the same divider on each so that the load on the PS is the same, but I only use one to go ahead and raise the heater. Similar to how Gordon Rankin did the PS for the Bugle.

B+ for each channel is formed from splited Pi filters coming from the same reservoir cap and the power consumption of the DC elevator shouldn't be considerable I think. I suppose It could be done with one voltage divider right after the reservoir cap. So, unless it is something deeper than I can dive - very likely - I guess it's all about schematics aesthetics.

 

[DavesNotHere]

other than solving for a layout issue on a board, there is no real advantage in a standard design. Referencing to the common output plate supply will do just fine in a stereo amp.