5V AC maining for filaments

mosfetmaster · 20th September 2010, 08:23 AM

Hello,

Is there any trouble maining 6.3V filaments with 5V AC?

Tanks

costis_n · 20th September 2010, 09:38 AM

yes. 5 V is too low , the valves will not work well. you need 6.1 to 6.3 Volts, AC or DC.

Tom Bavis · 20th September 2010, 02:49 PM

Plenty of 4.7-5 V tubes you could use, costing pretty much peanuts... 5V6, 5AQ5, 5CZ5 as power tubes, 5U8, 5GH8, 5AN8, 5BQ7 for preamp - 5HA7 or 5HC7 if you can find 12-pin sockets.

SY · 20th September 2010, 03:04 PM

6V transformers are even cheaper...

TheGimp · 20th September 2010, 03:15 PM

Schottky diodes and a big cap and you can run them off DC.

mosfetmaster · 20th September 2010, 03:43 PM

how?...

Frank Berry · 20th September 2010, 03:57 PM

A Bridge Rectifier using Schottky diodes followed by a big 20,000 microfarad cap should work.

mosfetmaster · 20th September 2010, 04:37 PM

Ah,yes...ok, but the question was not how to power DC voltage, but if is possible to power with lower AC voltage...

TheGimp · 20th September 2010, 04:42 PM

Schottky diodes are necessary as they have a very low voltage drop, around 0.3-0.5V per diode. If you use a diode bridge at less than half it's rated current you can hold the voltage drop to around 0.8V. So a 5 V transformer would provide (5*1.414)-0.8=6.27V to the heaters.

If you run the heaters at less than nominal-5%, the tubes don't work well.

Merlinb · 20th September 2010, 04:45 PM

Quote:

Originally Posted by mosfetmaster

Ah,yes...ok, but the question was not how to power DC voltage, but if is possible to power with lower AC voltage...

Yes you can, at least with preamp valves, but the characteristics of the valves will not match the data sheet. (lower gm, higher internal resistance).

Reduced heater voltage is not recommended for rectifier valves or power valves.

20th September 2010, 08:23 AM	#1
mosfetmaster diyAudio Member Join Date: May 2010	5V AC maining for filaments Hello, Is there any trouble maining 6.3V filaments with 5V AC? Tanks

20th September 2010, 03:04 PM	#4
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	6V transformers are even cheaper... __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

20th September 2010, 03:57 PM	#7
Frank Berry diyAudio Member Join Date: Sep 2003 Location: Midland, Michigan	A Bridge Rectifier using Schottky diodes followed by a big 20,000 microfarad cap should work. __________________ Frank

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20th September 2010, 09:38 AM	#2
costis_n Tinkerer diyAudio Member Join Date: Aug 2008	yes. 5 V is too low , the valves will not work well. you need 6.1 to 6.3 Volts, AC or DC.

20th September 2010, 02:49 PM	#3
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	Plenty of 4.7-5 V tubes you could use, costing pretty much peanuts... 5V6, 5AQ5, 5CZ5 as power tubes, 5U8, 5GH8, 5AN8, 5BQ7 for preamp - 5HA7 or 5HC7 if you can find 12-pin sockets.

20th September 2010, 03:15 PM	#5
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	Schottky diodes and a big cap and you can run them off DC.

20th September 2010, 03:43 PM	#6
mosfetmaster diyAudio Member Join Date: May 2010	how?...

20th September 2010, 04:37 PM	#8
mosfetmaster diyAudio Member Join Date: May 2010	Ah,yes...ok, but the question was not how to power DC voltage, but if is possible to power with lower AC voltage...

20th September 2010, 04:42 PM	#9
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	Schottky diodes are necessary as they have a very low voltage drop, around 0.3-0.5V per diode. If you use a diode bridge at less than half it's rated current you can hold the voltage drop to around 0.8V. So a 5 V transformer would provide (5*1.414)-0.8=6.27V to the heaters. If you run the heaters at less than nominal-5%, the tubes don't work well.

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