Series wiring for heaters

XZur · 12th December 2005, 09:03 PM

How should I wire 2 tubes in series, in way to supply 12ax7 with 12v (shouldn't be using H tap pin), and one 6dj8 with 6v? Am not sure if simple series wiring will work for a 19v suppy. I am worried it will apply 9v to each equally.

ilimzn · 12th December 2005, 11:50 PM

12AX7 at 12V needs 150mA, 6DJ8 needs about 330, so no, this will not work. But, you could use 12AX7 strapped to 6.3V, that would be 300mA and a PCC88 equivalent (series heater equivalent of 6DJ8) also at 300mA in series connection, and that would require about 113.5-14V. Best would be to use a higher voltage and a series resistor to get less dependance on mains.
You could also use a resistor in parallel with the 12AX7 to match current of the 6DJ8 but then you have the problem of different heater characteristics, you will get varying currents during heat-up. A current source for heaters would help a little. The resistor in parallel with 12AX7 heater would be about 70 ohms, 68 is the closest 5% standard value but should work OK. The only thing is you are wasting power by conversion into heat on it, about 2.3W, so you need a 5W resistor at least. You may need to trim it a bit to get the right voltages.

XZur · 14th December 2005, 02:33 AM

Thanks.... crystal!

ALBQ · 14th December 2005, 03:01 AM

xZur & ilimzn,
I am not sure what I am missing here but, why not tie pins 4/5 together on the 12AX7 and run the tube at 6.3 volts? A 12AX7 is designed to operate at either 12.6V (pins4-5) or 6.3V (4/5-9). In either case the tube requires ~300mA to operate both halves of the filament. In this case you would simply run the 6DJ8 and 12AX7 filaments in parallel - provided your supply could provide 600ma-700ma required for both tubes
-ALBQ

6DJ8 - pins 4-5 (6.3V only)
12AX7 - pins 4/5-9 (6.3V) pins4-5 (12.6V)

ilimzn · 14th December 2005, 11:45 AM

If I understood correctly, XZur has a 19V supply available, but not a 6.3V

XZur · 19th December 2005, 02:43 AM

That's correct, exploring to use 19v for these tubes.

12th December 2005, 09:03 PM	#1
XZur diyAudio Member Join Date: Oct 2005	Series wiring for heaters How should I wire 2 tubes in series, in way to supply 12ax7 with 12v (shouldn't be using H tap pin), and one 6dj8 with 6v? Am not sure if simple series wiring will work for a 19v suppy. I am worried it will apply 9v to each equally.

14th December 2005, 03:01 AM	#4
ALBQ diyAudio Member Join Date: Dec 2003 Location: Albuquerque	6DJ8 - 12AX7 Filaments xZur & ilimzn, I am not sure what I am missing here but, why not tie pins 4/5 together on the 12AX7 and run the tube at 6.3 volts? A 12AX7 is designed to operate at either 12.6V (pins4-5) or 6.3V (4/5-9). In either case the tube requires ~300mA to operate both halves of the filament. In this case you would simply run the 6DJ8 and 12AX7 filaments in parallel - provided your supply could provide 600ma-700ma required for both tubes -ALBQ 6DJ8 - pins 4-5 (6.3V only) 12AX7 - pins 4/5-9 (6.3V) pins4-5 (12.6V)

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
PL519 Heaters in series blow fuse	wiysel	Tubes / Valves	5	6th November 2008 11:18 AM
AC wiring heaters, A or B ?	zigzagflux	Tubes / Valves	10	4th July 2008 09:43 PM
Tube heaters in series.	nigelwright7557	Tubes / Valves	5	4th July 2008 09:11 PM
Tube current regulation for series heaters' supply.	engels	Tubes / Valves	4	5th August 2007 10:49 PM
Series heaters = small problem?	Klimon	Tubes / Valves	5	13th May 2007 11:12 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

12th December 2005, 11:50 PM	#2
ilimzn diyAudio Member Join Date: Feb 2005 Location: Zagreb	12AX7 at 12V needs 150mA, 6DJ8 needs about 330, so no, this will not work. But, you could use 12AX7 strapped to 6.3V, that would be 300mA and a PCC88 equivalent (series heater equivalent of 6DJ8) also at 300mA in series connection, and that would require about 113.5-14V. Best would be to use a higher voltage and a series resistor to get less dependance on mains. You could also use a resistor in parallel with the 12AX7 to match current of the 6DJ8 but then you have the problem of different heater characteristics, you will get varying currents during heat-up. A current source for heaters would help a little. The resistor in parallel with 12AX7 heater would be about 70 ohms, 68 is the closest 5% standard value but should work OK. The only thing is you are wasting power by conversion into heat on it, about 2.3W, so you need a 5W resistor at least. You may need to trim it a bit to get the right voltages.

14th December 2005, 02:33 AM	#3
XZur diyAudio Member Join Date: Oct 2005	Thanks.... crystal!

14th December 2005, 11:45 AM	#5
ilimzn diyAudio Member Join Date: Feb 2005 Location: Zagreb	If I understood correctly, XZur has a 19V supply available, but not a 6.3V

19th December 2005, 02:43 AM	#6
XZur diyAudio Member Join Date: Oct 2005	That's correct, exploring to use 19v for these tubes.