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Elevating heaters in separate channels together
Elevating heaters in separate channels together
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Old 18th January 2017, 06:10 PM   #1
geezertron is offline geezertron  United States
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Default Elevating heaters in separate channels together

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?
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Old 18th January 2017, 06:24 PM   #2
Ketje is offline Ketje  Belgium
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As long as the elevated voltage is well decoupled to ground i see no problem.
Mona
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Old 18th January 2017, 07:34 PM   #3
MagicBus is offline MagicBus  Greece
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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?
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Old 18th January 2017, 07:55 PM   #4
Ketje is offline Ketje  Belgium
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If he had used only one the other would feel neglected :lol:
Mona
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Old 18th January 2017, 08:07 PM   #5
MagicBus is offline MagicBus  Greece
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Quote:
Originally Posted by Ketje View Post
If he had used only one the other would feel neglected :lol:
Mona
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Old 18th January 2017, 08:25 PM   #6
geezertron is offline geezertron  United States
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Quote:
Originally Posted by Ketje View Post
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.
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Old 18th January 2017, 08:48 PM   #7
DF96 is offline DF96  England
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Two resistors means that you still get some elevation if one channel loses its supply rail. I'm not sure that matters, though.
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Old 18th January 2017, 08:59 PM   #8
smbrown is offline smbrown  United States
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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.
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Old 19th January 2017, 06:50 AM   #9
MagicBus is offline MagicBus  Greece
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Quote:
Originally Posted by DF96 View Post
Two resistors means that you still get some elevation if one channel loses its supply rail. I'm not sure that matters, though.
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Originally Posted by smbrown View Post
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.
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Old 20th January 2017, 12:30 PM   #10
DavesNotHere is offline DavesNotHere  United States
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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.
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