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Old 8th March 2008, 02:31 PM   #1
G is offline G  United States
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Default 5.3v on 6SN7 filament?

What are the liabilities of running 5.3 volts DC on 6SN7 filaments?
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Old 8th March 2008, 03:09 PM   #2
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Lower gm, higher rp and shorter lifespan
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Old 8th March 2008, 03:17 PM   #3
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If you don't run them very conservatively, you can deplete the space charge and damage the cathode.

See:
http://www.diyaudio.com/forums/showt...80#post1441880
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Old 8th March 2008, 03:35 PM   #4
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Thanks for the answers. I was just curious.
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Old 11th March 2008, 02:56 AM   #5
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Let me guess - you are rectifying a 5V winding originally intended to supply the tube rectifier heater/cathode.

I've done this myself BUT using schottky diodes. In the amp concerned, a 5V 2A winding with schottky diode bridge and 10,000uF/25V electrolytic pushed 5.95V DC into a 12AX7 heater (0.3 Amps draw) very nicely.
I used 4 off 1N5822 (40 Volt 3 Amp) schottky diodes for the bridge.
These things aren't real cheap but when I looked at replacing 2 of them with a MBR20100CT (dual 100V 20A with common cathode in a TO-220 pack) to save some bucks I found that the voltage drop was significantly higher.
Looking at the heater supply with a CRO (in circuit with the whole amp running) I did see a few small spikes projecting out of the ripple which went away when I sat the whole supply on a +60V DC supply derived from the main HT.

Heater Voltage Specification is +/- 5%. 6.3 - 5% is 5.97V. As far as I'm concerned the 5.95 is "in spec" (ish) whereas 5.3 is not.

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