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Old 7th October 2003, 12:18 PM   #11
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Hi Frank,

Thanks for the info. it was very interesting to read.
As I stated before, I have a 50bm8 amp running at 45 v filament currently running with no impact on sound (as much as I know) and I had several others that worked well - until I took them apart for other projects, but after reading your mail I will test it again.

Thanks.

Glass_painter
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Old 7th October 2003, 12:53 PM   #12
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Hi,

Quote:
As I stated before, I have a 50bm8 amp running at 45 v filament currently running with no impact on sound (as much as I know) and I had several others that worked well
Ah...if I'm not mistaken the 50BM8s' heater was designed for series operation ( several heaters strung together daisy chain) in radio and TV service.
If that's the case it will work as long as it can draw its required current (100mA in this case), voltage isn't as critical here. Current draw is.

I'd need to refresh the little I know about it though, never took any interest in those particular TV tubes but most audio tubes have equivalents using different heater voltages for this kind of service.

If my guesswork is correct it could well explain why you don't hear a difference at lower heater voltage.

Cheers,
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Old 7th October 2003, 07:21 PM   #13
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Hi Frank,

Come to think of it, most of my tubes are with "TV" filament. Maybe this is why I have not noticed the phenomenon so far.
why would there be any difference between the two? it is only a heater coil with the same wattege just different voltage.

Thanks.

Glass painter.
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Old 7th October 2003, 07:32 PM   #14
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Hi,

Quote:
why would there be any difference between the two? it is only a heater coil with the same wattege just different voltage.
Most TV tubes at a given point in history had a heater designed for stringed operation.

The idea was to save on powerxformers by putting the heaters in series so you ended up with, say, 115 VAC for a TV set in the U.S. using a combination of tubes.

As you may have noticed the higher the voltage the lower the current consumption making for better efficiency. Less power consumption was the main target.

How this was achieved technically I don't quite remember but a book on the history of the electron tube should explain it.

Or perhaps someone else remembers the details?

Sorry if I'm not much help to you here...

Cheers,
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