Ok, I have the extra resistors from the partsbuy and the only thing missing is one pair of TO-3s and those I can "liberate" from my friends leftovers so thats no problem. And you're right, there are holes pre-drilled for another pair and I have the current to spare. 
I have no problem with the extra heat but it is the devices I worry about (ofcourse) and y fancontroll starts to make quite a racket when the temperature goes above 60degrees celsius.
But first I must desolder and check all transistors but that will have to wait another two weeks since I'm waiting for a couple of things. A pair of 6,8ohm powerresistors (225W) among other things and I might as well do everything at the same time otherwise I won't get around to it...
I have no problem with the extra heat but it is the devices I worry about (ofcourse) and y fancontroll starts to make quite a racket when the temperature goes above 60degrees celsius.
But first I must desolder and check all transistors but that will have to wait another two weeks since I'm waiting for a couple of things. A pair of 6,8ohm powerresistors (225W) among other things and I might as well do everything at the same time otherwise I won't get around to it...
Hi,
a fanned type heatsink has the fins considerably closer together than a passive heatsink.
the fin gaps are about 7 to 10mm on a passive.
and about 2 to 4mm on a fanned. They are made differently and do not work well if interchanged.
The fanned type also works better if it is oriented the same as passive i.e. fan flow bottom to top.
Also the fan works better if it is PUSHING the airflow, it has the additional advantage that the fan operates in the cool airstream and that prolongs life.
a fanned type heatsink has the fins considerably closer together than a passive heatsink.
the fin gaps are about 7 to 10mm on a passive.
and about 2 to 4mm on a fanned. They are made differently and do not work well if interchanged.
The fanned type also works better if it is oriented the same as passive i.e. fan flow bottom to top.
Also the fan works better if it is PUSHING the airflow, it has the additional advantage that the fan operates in the cool airstream and that prolongs life.
AndrewT, your statement "The fanned type also works better if it is oriented the same as passive i.e. fan flow bottom to top" is true, but pure theoretical.
With airtemp. from 20 C/50% to 60 C/5,9% and a ductlength of 18 cm, gives you about only 0,25 Pa extra static pressure. No argument to make the airflow going from bottem to top i.m.o.
With airtemp. from 20 C/50% to 60 C/5,9% and a ductlength of 18 cm, gives you about only 0,25 Pa extra static pressure. No argument to make the airflow going from bottem to top i.m.o.
The lower the fanspeed (and airflow) the bigger the influence
of flow direction (bottom to top or top to bottem thats for sure.
Still peanuts i think, but i must say i do not know the value of the pressure difference that is needed for your tunnel and your airflow. I think that this value is in the range of 5 or 10 Pa.
of flow direction (bottom to top or top to bottem thats for sure.
Still peanuts i think, but i must say i do not know the value of the pressure difference that is needed for your tunnel and your airflow. I think that this value is in the range of 5 or 10 Pa.
fan mounting/ rubber
My lower fan is mounted on soft rubber grommets that I split in half with a utility knife, so they are kind of like shoulder washers, the bolts that mount the fan never actually touch the fan they only touch the rubber. And the fan touches no metal, it only touches rubber.
At the time I thought this would help make it quieter (less vibration noise), and since it requires major disassembly to change this fan around I did not want to have to mess with it in the future. I thought that the rubber under the fan would also advantageously space the fan from the grill holes a small amount to make it quieter still (less vent hole noise).
However, you then have to choose how hard to mount the fan, because you are really going to squish that rubber if you mount it very securely. My guess is that too tight and you lose the advantages of the soft rubber, too lose and your mounting bolts are going to eventually come off.
If you look at the pic you see the fan and the rubber that is being squished (follow the red arrows). The vertical heat sink mounts onto the white nylon standoffs.
You also see the fan vent holes which according to ununamious consent in this thread are too small and too few. Yes, had I done better venting I'm sure it would be even quieter than using rubber. I just was tired of drilling holes in the bottom plate and wanted to assemble the amp. sorry. There are actually additional holes under the tiny fan but I got tired and did not want to drill them all over the place.... After a year of construction I wanted the amp to be built.
jacco vermeulen said:
My lower fan is mounted on soft rubber grommets that I split in half with a utility knife, so they are kind of like shoulder washers, the bolts that mount the fan never actually touch the fan they only touch the rubber. And the fan touches no metal, it only touches rubber.
At the time I thought this would help make it quieter (less vibration noise), and since it requires major disassembly to change this fan around I did not want to have to mess with it in the future. I thought that the rubber under the fan would also advantageously space the fan from the grill holes a small amount to make it quieter still (less vent hole noise).
However, you then have to choose how hard to mount the fan, because you are really going to squish that rubber if you mount it very securely. My guess is that too tight and you lose the advantages of the soft rubber, too lose and your mounting bolts are going to eventually come off.
If you look at the pic you see the fan and the rubber that is being squished (follow the red arrows). The vertical heat sink mounts onto the white nylon standoffs.
You also see the fan vent holes which according to ununamious consent in this thread are too small and too few. Yes, had I done better venting I'm sure it would be even quieter than using rubber. I just was tired of drilling holes in the bottom plate and wanted to assemble the amp. sorry. There are actually additional holes under the tiny fan but I got tired and did not want to drill them all over the place.... After a year of construction I wanted the amp to be built.
Attachments
Fan Talk
All this fan talk just makes me want to post. I wanted to hold back until finished but I can't hold a secret for more than a day.
I'm going with a fan and a total of six outputs per channel. I love to hate fans so I purchased some new technology liscesned by Sony to Scythe. It is a S-FLEX SFF21F
I'm going to use MICREL MIC502 to try and make it even more quiet and provide emergency protection.
I'm wrestling with aluminum these days!
Cheers,
Shawn.
All this fan talk just makes me want to post. I wanted to hold back until finished but I can't hold a secret for more than a day.
I'm going with a fan
and a total of six outputs per channel. I love to hate fans so I purchased some new technology liscesned by Sony to Scythe. It is a S-FLEX SFF21F I'm going to use MICREL MIC502 to try and make it even more quiet and provide emergency protection.
I'm wrestling with aluminum these days!
Cheers,
Shawn.
Attachments
Hi KmJ,
I don't think your overheating problem is lack of airflow.
I think you still have an amplifier error.
Turn your bias current (Iq) right down to near zero (maximum resistance in the lower leg of the Vbe multiplier).
Insert a light bulb in series with the mains live supply lead.
Turn on and tell us what the light bulb is doing. Flash? dim? bright? off?
I suggest you work with just one channel at a time. Disconnect the channel from the transformer until the other is sorted and insulate the disconnected leads.
I don't think your overheating problem is lack of airflow.
I think you still have an amplifier error.
Turn your bias current (Iq) right down to near zero (maximum resistance in the lower leg of the Vbe multiplier).
Insert a light bulb in series with the mains live supply lead.
Turn on and tell us what the light bulb is doing. Flash? dim? bright? off?
I suggest you work with just one channel at a time. Disconnect the channel from the transformer until the other is sorted and insulate the disconnected leads.
I would guess so. I think that instead of checking all transisitors I'll just order some new, check them and replace all. Not the output ones but the ones on the mainboard, then I'll dissconnect the outputs and check. It will however take a few weeks since I'm of on vacation soon. I'll try to do some of the work this week but no promises
Any fan pulling hot air out over itself will have a drastically shorteded life span. I had an arguement with a guy from Crown at a recent Theater convention in Florida as to weather an amps fan should "suck or blow". Even though he claimed he had all sorts opf dtat to substantiate why Crown did it their way I still won the arguement with him. He was completely frazzled when I got done debating it
. BGW used to do the same thing too but Brian was a friend so I never argued the point with him.
Mark
. BGW used to do the same thing too but Brian was a friend so I never argued the point with him.Mark