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Old 21st January 2009, 10:43 PM   #1
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Default series or parallel?

i hate to keep bothering everyone over this amp problem of mine but i have posted a link with the schematics and was wandering if someone could tell me whether the filaments were in series or not. thanks, wendell.

http://techpreservation.dyndns.org/b...Schematics.pdf
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Old 22nd January 2009, 03:26 AM   #2
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The filaments are in parallel.
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Old 22nd January 2009, 05:19 AM   #3
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Strange , but I only see a 6.3V source for heater filaments on this schematic. What are they using to power the 12AT7's heater filaments ?


.............................Blake
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Old 22nd January 2009, 05:31 AM   #4
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12AX7,12AU7,12AT7 (and many other) filaments can be powered two ways - pin 9 is the centertap of pins 4 and 5.

So ... 12.6 volts to pins 4 and 5, or, 6.3 volts - one side to pins 4 and 5 shorted, the other side to pin 9.

As a 12.6 volt filament, the tube will draw 300 ma - as a 6.3, 600 ma.

Look at the datasheet for the tube on http://www.duncanamps.com - it will be apparent.

If not, many are here with much more knowledge than me.
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Old 22nd January 2009, 10:31 AM   #5
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Default amp dead

so would it be safe to assume that the transformer would be the culprit?
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Old 22nd January 2009, 04:42 PM   #6
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Thanks Charley ! I was unaware of the optional 6-12V heater arrangement !


Medicman ,

amp is dead!

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