Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: archaos on July 15, 2011, 06:56:02 am

Title: Cooling fan : AC or DC supply ?
Post by: archaos on July 15, 2011, 06:56:02 am

Hi guys, all is in the title. Yet I wish to install the fan with an independent power supply ; Merlin's power supply book says that DC fan too close from the preamp can induce noise.

Thanks for your inputs, ideas, suggestions.  :worthy1:

               

Title: Re: Cooling fan : AC or DC supply ?
Post by: LooseChange on July 15, 2011, 07:42:06 am

You don't need a fan on the preamp tubes so DC will be fine.
I made a simple DC power supply coming off the 6.3v heater supply. I ran a 12vdc fan. Since it ran at around 8vdc it ran a bit slower and was very quiet.

Title: Re: Cooling fan : AC or DC supply ?
Post by: archaos on July 15, 2011, 08:53:17 am

Thank you.

Title: Re: Cooling fan : AC or DC supply ?
Post by: tubeswell on July 15, 2011, 09:44:52 am

DC is quieter/less hum-prone

Title: Re: Cooling fan : AC or DC supply ?
Post by: jojokeo on July 15, 2011, 10:29:43 am

Can it be as simple to just throw in two 1n4007 diodes off the heater wires and hook the fan right up to that? But then what if the heater's are raised to a higher AC voltage...? I'm guessing it wouldn't matter or would it since it's only a ground "reference" so it would still only see the 6.3DCv like the heaters?

Title: Re: Cooling fan : AC or DC supply ?
Post by: tubeswell on July 15, 2011, 10:42:08 am

Quote from: jojokeo on July 15, 2011, 10:29:43 am

Can it be as simple to just throw in two 1n4007 diodes off the heater wires and hook the fan right up to that? But then what if the heater's are raised to a higher AC voltage...? I'm guessing it wouldn't matter or would it since it's only a ground "reference" so it would still only see the 6.3DCv like the heaters?

I think it you did that you would get the effect of humps from the rectified pulses going back into the ground return path

Title: Re: Cooling fan : AC or DC supply ?
Post by: phsyconoodler on July 15, 2011, 10:51:34 am

Old Traynor amps used AC fans that were slowed down with a big resistor.They weren't noisy,but the olf fans often fell apart after a few years,just like old fans of the day.They weren't built particularly well.A small modern 115v fan would be fine I should think.

Title: Re: Cooling fan : AC or DC supply ?
Post by: LooseChange on July 15, 2011, 11:08:28 am

Quote from: jojokeo on July 15, 2011, 10:29:43 am

Can it be as simple to just throw in two 1n4007 diodes off the heater wires and hook the fan right up to that? But then what if the heater's are raised to a higher AC voltage...? I'm guessing it wouldn't matter or would it since it's only a ground "reference" so it would still only see the 6.3DCv like the heaters?

Need to add a filter cap. Like 1000uf @ 16v (just a guess)

Title: Re: Cooling fan : AC or DC supply ?
Post by: jojokeo on July 15, 2011, 11:39:56 am

Is there a recommended schematic or anything for a simple 4" computer fan? I have a couple laying around if I want to go this route.

Title: Re: Cooling fan : AC or DC supply ?
Post by: phsyconoodler on July 15, 2011, 01:01:13 pm

Weber has a schematic on his site for hooking up a fan.

Title: Re: Cooling fan : AC or DC supply ?
Post by: jjasilli on July 15, 2011, 01:20:43 pm

Here's how I did it.

Title: Re: Cooling fan : AC or DC supply ?
Post by: jojokeo on July 15, 2011, 01:38:11 pm

Thanks for the schem. - I have < 40vdc applied to the heater artificial CT - do you think this will affect anything or cause something else to be needed?

Title: Re: Cooling fan : AC or DC supply ?
Post by: archaos on July 15, 2011, 01:39:28 pm

Quote from: jjasilli on July 15, 2011, 01:20:43 pm

Here's how I did it.

Which software allows to read your schematic ?

Title: Re: Cooling fan : AC or DC supply ?
Post by: jojokeo on July 15, 2011, 01:44:20 pm

Go here and D/L the Jschem program for your operating system

http://www.el34world.com/Forum/index.php?topic=763.0 (http://www.el34world.com/Forum/index.php?topic=763.0)

Title: Re: Cooling fan : AC or DC supply ?
Post by: kagliostro on July 15, 2011, 02:08:12 pm

A simply two speed schematic

http://taweber.powweb.com/store/fan_schem.jpg (http://taweber.powweb.com/store/fan_schem.jpg)

http://taweber.powweb.com/store/modkits.htm#fan (http://taweber.powweb.com/store/modkits.htm#fan)

Kagliostro

Title: Re: Cooling fan : AC or DC supply ?
Post by: archaos on July 15, 2011, 03:08:34 pm

Thanks a lot guys !