5.3v on 6SN7 filament?

G · 8th March 2008, 02:31 PM

What are the liabilities of running 5.3 volts DC on 6SN7 filaments?

Fuling · 8th March 2008, 03:09 PM

Lower gm, higher rp and shorter lifespan

SpreadSpectrum · 8th March 2008, 03:17 PM

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

G · 8th March 2008, 03:35 PM

Thanks for the answers. I was just curious.

gingertube · 11th March 2008, 02:56 AM

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.

Cheers,
Ian

8th March 2008, 02:31 PM	#1
G diyAudio Member Join Date: Apr 2002 Location: Belleville, IL.	5.3v on 6SN7 filament? What are the liabilities of running 5.3 volts DC on 6SN7 filaments? __________________ Gavin

8th March 2008, 03:35 PM	#4
G diyAudio Member Join Date: Apr 2002 Location: Belleville, IL.	Thanks for the answers. I was just curious. __________________ Gavin

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8th March 2008, 03:09 PM	#2
Fuling diyAudio Member Join Date: Aug 2001 Location: Sweden (Mora)	Lower gm, higher rp and shorter lifespan

8th March 2008, 03:17 PM	#3
SpreadSpectrum diyAudio Member Join Date: Nov 2007	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

11th March 2008, 02:56 AM	#5
gingertube diyAudio Member Join Date: Oct 2004 Location: Adelaide South Oz	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. Cheers, Ian

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