Help,
I recently told a fellow audiophile that i was going to fit a cooling fan to my latest tube amp project. His response was a flat "fans do not belong in HiFi Amplifiers".
I believe there MUST be suitable engineering solution to adding a fan to a tube amp which can only enhance its reliability.
Yes there are acoustic noise level issues to solve but it should be practical.
There are a couple of "rules of thumb" and application hints like:
1) Always use the fan to blow INTO the equipment so that the box acts as an acoustic baffle.
2) Use a DC fan and run it at half voltage
etc.
I believe that it is more important to choose the right sort of fan in the first place - the problem is that I don't know what that type might be.
Any ideas/suggestions?
Cheers,
Ian
I recently told a fellow audiophile that i was going to fit a cooling fan to my latest tube amp project. His response was a flat "fans do not belong in HiFi Amplifiers".
I believe there MUST be suitable engineering solution to adding a fan to a tube amp which can only enhance its reliability.
Yes there are acoustic noise level issues to solve but it should be practical.
There are a couple of "rules of thumb" and application hints like:
1) Always use the fan to blow INTO the equipment so that the box acts as an acoustic baffle.
2) Use a DC fan and run it at half voltage
etc.
I believe that it is more important to choose the right sort of fan in the first place - the problem is that I don't know what that type might be.
Any ideas/suggestions?
Cheers,
Ian
Hi,
Well...
If you must cool tubes why not take a look at what Bill Perkins of Pearl-Hifi came up with?
I think the major concern with the heat generated by the tubes and power resistors is a long-term reliability issue, caps drying out due to excessive heat etc.
Most of this can be circumvented by careful layout and providing sufficient airflow IME, still:
TUBE COOLERS
Cheers,😉
Well...
If you must cool tubes why not take a look at what Bill Perkins of Pearl-Hifi came up with?
I think the major concern with the heat generated by the tubes and power resistors is a long-term reliability issue, caps drying out due to excessive heat etc.
Most of this can be circumvented by careful layout and providing sufficient airflow IME, still:
TUBE COOLERS
Cheers,😉
I'm with fdegrove, heat problems in tube circuits are really layout/ventillation problems in disguise. Make sure that the tubes are properly spaced and allow for air flow around the base of power tubes, either by drilling holes in the chassis or having an oversized hole around the socket with the socket mounted on the circuit board or standoffs. Make sure that there's a place for cool air to enter the chassis. I can't count the number of times that I've seen equipment with air holes in the top (where the builder or customer could look in and observe the glowing tubes), but none on the sides or bottom where air could enter. I like looking at tubes as much as the next guy, but I also like knowing that there's sufficient ventillation.
Incidentally, a good rule of thumb is to space tubes at least two tube-diameters apart, on center. If you have a 1.5" tube, set them 3" apart or more. Some spec sheets have recommended minimum spacings. If so, adhere to them.
With attention to details, convection is sufficient. It's completely silent and doesn't introduce magnetic fields into your circuitry. And it costs less, too.
Grey
Incidentally, a good rule of thumb is to space tubes at least two tube-diameters apart, on center. If you have a 1.5" tube, set them 3" apart or more. Some spec sheets have recommended minimum spacings. If so, adhere to them.
With attention to details, convection is sufficient. It's completely silent and doesn't introduce magnetic fields into your circuitry. And it costs less, too.
Grey
The problem children
I've done as above as much as possible - the tubes are a liitle close together for my complete satisfaction BUT this was dictated by the PCB I used (Menno van der Venne BBB70100).
40mm holes around the EL34s which plug thru into a PCB.
No bases on the boxes as yet hence them sitting on the timber to allow air flow from underneath.
EL34s in triode mode giving about 40 watts Output Power.
Thanks,
Ian
I've done as above as much as possible - the tubes are a liitle close together for my complete satisfaction BUT this was dictated by the PCB I used (Menno van der Venne BBB70100).
40mm holes around the EL34s which plug thru into a PCB.
No bases on the boxes as yet hence them sitting on the timber to allow air flow from underneath.
EL34s in triode mode giving about 40 watts Output Power.
Thanks,
Ian
Attachments
I have little area to play with stereo equipment in my house, so building compact is a must. This means undersized cabinets and fan cooling. Just use a quiet computer fan. Local thrift stores sell them (new and pulls) for 50 cents to $2. I snagged the whole box and reserve the quiets for HiFi 🙂
Bah, I'm sitting next to three fans right now. I can't hear them worth a damn, the music is 10-20dB louder than them 😀
At worst, you can add acoustic damping materials, ducting and whatnot to keep the sound both contained and damped.
Tim
At worst, you can add acoustic damping materials, ducting and whatnot to keep the sound both contained and damped.
Tim
Output tubes: designed to run hot... But leave a good spacing between them, a ventilation gap at the base (or drilled holes) and if possible mount them down into the chassis a little. Also don't run them past their ratings, even in class A.
Power resistors: Mount as far away from capacitors and other circuitry as practical. If possible have some mesh above them.
One thing that is useful is chassis ventialtion: by having some places for hot air to escape, cold air can be drawn in through the bottom of the amp and keep it cool.
But:
If you do use a fan, I would mount it actually in the base of the amp, blowing upwards (ie sucking cold air from underneath the amp.) Use a 12V "stealth" fan running at 6VDC for maximum quietness. You can buy quiet PC fans (for example the Vantec stealth) and even in low profile.
Power resistors: Mount as far away from capacitors and other circuitry as practical. If possible have some mesh above them.
One thing that is useful is chassis ventialtion: by having some places for hot air to escape, cold air can be drawn in through the bottom of the amp and keep it cool.
But:
If you do use a fan, I would mount it actually in the base of the amp, blowing upwards (ie sucking cold air from underneath the amp.) Use a 12V "stealth" fan running at 6VDC for maximum quietness. You can buy quiet PC fans (for example the Vantec stealth) and even in low profile.
I generally build amps vertically, with the PS at the bottom and the analog sections at or near the top. I leave lots of space between tubes, holes/spaces around sockets etc, room for air to enter, and I think about the thermal design as I lay it out. No heat issues here. However, I have used fans to cool before when I've used transmitter tubes, run at low speed (damn near silent from listening position) from the bottom pushing the air up past the tubes. In my house it can easily get into the high 30's in summer.
Would you gentlemen please not remind me of high temperatures. My circulating pump failed last night night and I'm waiting for the system to drain down sufficiently so that I can replace it (the valves either side didn't work). As I shiver here, I can assure you that my amplifiers currently have no cooling problems whatsoever.
You can get a surprising amount of airflow just by using the power of convection. The Apple G4 cube is a good example, where all the heatsinks are arranged around a central 'chimney' and air is drawn up through the unit. Judging by the amount of dust that collects underneath, a fair amount of air is getting moved.
It's quite a neat solution which avoids having to use a fan and has allowed them to use a very small case without overheating.
And no, I don't have shares in Apple, I just like the thing
It's quite a neat solution which avoids having to use a fan and has allowed them to use a very small case without overheating.
And no, I don't have shares in Apple, I just like the thing
Re: The problem children
Hello Ian, would those be the Plitron Boards? How do they sound?
Regards
Anthony
gingertube said:
Hello Ian, would those be the Plitron Boards? How do they sound?
Regards
Anthony
SHiFTY said:
Yes....snap....exactly my technique. If you use a brushless type at 1/3 voltage (to cut the drumming down) it may need a high value shunt cap across a series resistor to give it that little extra inertia on switch-on., then it will settle down.
The biggest drawback in my main amp is reflected radiation coming off the tubes and getting the chassis hot even with ample ventilation. Drilling large holes around the tube skirts is obvious. A large chassis with tubes mounted at 4 inch centers to one another using double quads 6550/88's etc in push pull, the chassis after an hour reaches 40-50°C, even though there aren't any wirewounds underneath. It becomes obvious to mount the power supply electrolytics well away from any heat source. For every 10°C temp rise, these components drastically reduce their working life compared to the life of tubes operated within their margins.
However, even the fan woring on reduced 1/3 speed the noise of is way above the S/N ratio of the amp.......unless (like me) one likes ones sound really loud then it doesn't matter.
rich
Response to Coulomb
Yep - they are the Plitron Boards.
How does it sound??
In Ultralinear Mode Output Impedance is 13 Ohms so it sounds highly coloured as power out tracks the speaker impedance vs frequency characteristic.
In Triode Mode Output Impedance is 5 Ohms and it actually sounds quite lovely with my nominally 6 Ohm speakers (DF = 1.2)
You can hear those crystal clear, tingly highs that are so hard to get from an amp.
If you are serious about building an amp on a PCB and want to use Plitron trannies, I would suggest that you try to get the VDV100 PCBs (maybe from Amplimo?) in preference to the BBB70100 boards. Its a better circuit with higher sensitivity.
Cheers,
Ian
Yep - they are the Plitron Boards.
How does it sound??
In Ultralinear Mode Output Impedance is 13 Ohms so it sounds highly coloured as power out tracks the speaker impedance vs frequency characteristic.
In Triode Mode Output Impedance is 5 Ohms and it actually sounds quite lovely with my nominally 6 Ohm speakers (DF = 1.2)
You can hear those crystal clear, tingly highs that are so hard to get from an amp.
If you are serious about building an amp on a PCB and want to use Plitron trannies, I would suggest that you try to get the VDV100 PCBs (maybe from Amplimo?) in preference to the BBB70100 boards. Its a better circuit with higher sensitivity.
Cheers,
Ian
The original issue
I dragged out my source material - in this case "Electronics Cooling" Journal and looked thru' a couple of relevant articles.
The fan type required IS an axial fan which is what everyone above has been talking about. Axial Fans are most suited to low pressure/high flow rate application. ONLY if you are trying to work agains a significant back pressure should you use a radial fan (sometimes called a blower) instead.
For low acoustic noise you want to keep airflow impedances low - by that we mean large air inlet, large air outlet (around each valve). There is some evidence to suggest that more fan blades are quieter than less blades at the same flow rate. Ie choose the 7 blade fan over the 5 blade fan.
Other evidence suggests a larger fan at slower speed is much quieter than a smaller fan at higher speed.
This also stacks up with the fact that we are only trying to provide a small positive pressure inside the box to bias or reinforce convective airflow.
In addition there are some axial fans designed specifically for low acoustic noise. A feather on the traling edge of the fan blade appears to be one way to reduce noise. Also sleeve bearings appear to be quieter than ball bearings.
So blow into the box from beneath - this allows the box to act as an acoustic baffle/damper - this action can be enhanced with a bit of acoustic damping material inside the box. Make sure you have no mechanical resonances - to this end use dampers on the fan mounts.
There - more than you probably ever wanted to know about fans.
Cheers,
Ginger
I dragged out my source material - in this case "Electronics Cooling" Journal and looked thru' a couple of relevant articles.
The fan type required IS an axial fan which is what everyone above has been talking about. Axial Fans are most suited to low pressure/high flow rate application. ONLY if you are trying to work agains a significant back pressure should you use a radial fan (sometimes called a blower) instead.
For low acoustic noise you want to keep airflow impedances low - by that we mean large air inlet, large air outlet (around each valve). There is some evidence to suggest that more fan blades are quieter than less blades at the same flow rate. Ie choose the 7 blade fan over the 5 blade fan.
Other evidence suggests a larger fan at slower speed is much quieter than a smaller fan at higher speed.
This also stacks up with the fact that we are only trying to provide a small positive pressure inside the box to bias or reinforce convective airflow.
In addition there are some axial fans designed specifically for low acoustic noise. A feather on the traling edge of the fan blade appears to be one way to reduce noise. Also sleeve bearings appear to be quieter than ball bearings.
So blow into the box from beneath - this allows the box to act as an acoustic baffle/damper - this action can be enhanced with a bit of acoustic damping material inside the box. Make sure you have no mechanical resonances - to this end use dampers on the fan mounts.
There - more than you probably ever wanted to know about fans.
Cheers,
Ginger
Judging from the photo, I don't see that you have any problems. Is there some reason that you're convinced that you need fans?
Grey
Grey
UK catalogues specify the noise (dB(A) @ 1m) and airflow of fans. Something you need to watch out for is that DC fans (12V, 24V etc) use semiconductor commutators and regulators. Lowering the applied voltage to reduce noise only works on traditional fans - doesn't make a blind bit of difference to a modern fan. However, you can get thermostatically controlled fans that bring the control element outside to a thermocouple - possibly allowing substitution of a fixed resistor to slow the fan. Unfortunately, my experience is that motor commutation/vibration is subjectively more of a problem than blade noise.
Grey and EC8010
Ec8010 is correct about comutator noise etc.
BUT
Grey,
The ONLY electrolytics I could get to fit the PCB (4 off 47uF 500V axial for each board) were 85 degrees C jobs. In addition our forcast for tomorrow is 38 degrees Celsius - Sorry EC8010 to harp about the heat when your freezing your buns at the moment. I run my house aircon at about 26 to 27 degrees to keep the power bills sort of under control.
The boxes adjacent to the power valves get quite hot to touch - probably around 50 degrees C.
Thats why I want to put in afan.
Cheers,
Ian
Ec8010 is correct about comutator noise etc.
BUT
Grey,
The ONLY electrolytics I could get to fit the PCB (4 off 47uF 500V axial for each board) were 85 degrees C jobs. In addition our forcast for tomorrow is 38 degrees Celsius - Sorry EC8010 to harp about the heat when your freezing your buns at the moment. I run my house aircon at about 26 to 27 degrees to keep the power bills sort of under control.
The boxes adjacent to the power valves get quite hot to touch - probably around 50 degrees C.
Thats why I want to put in afan.
Cheers,
Ian
- Status
- Not open for further replies.