I have sufficient heat sinking to run passive and bias the amp reasonably high, but don't have real estate for a large amp. I am thinking of going with half the heat sinking + a decent fan. I am thinking running the fan at low rpm should be tolerable noice wise, I don't think I would need to move too much air.
What do you guys think?
What do you guys think?
I have the antek 18v 300w toroid for this project, and I see it has a shield (purple wire). I'm not clear about what to do with this, I don't see it in the writeup PDF. I think of it as being in this big field, so I hesitate to just attach it to ground. What does the brain trust say?
Thx!
Thx!
Connect the power transformer shield wire to the chassis ground (safety ground).
I did this, but with about 70% of the heatsink of the smallest Nelson-recommended chassis. I posted about it several times in early April of this year in this thread, starting here https://www.diyaudio.com/community/threads/f5m-kit.408290/post-7645211 and dribbling on for a few weeks.
Long story short, using good fan placement and keeping bias near 1.0 amp, my build works well and I don't hear the fans from my listening location. I'm not sure going to 50% of heat sink is a good idea, but if you have enough fan power and provide enough clearance below and above the chassis, I suppose it will be workable. If I was to do build another F5m (always tempted), I'd try harder/wait longer to get a chassis with external fins, either a Modushop one or a repurposed one.
I'd also say that when using a chassis with smaller heatsinks, it might be particularly helpful to use a 18V transformer, as that lower voltage will allow you to achieve higher bias current with less total heat dissipation than a higher-voltage transformer will (at least that is my understanding of the trade offs).
Hello all, (sorry in advance i'm really a dummy in electronic)
i have start welding and...
i have V1R1 power supply wich i have receive with my kit. But i have order exactly the list from Nelson in his file at first post and i see on this board there is 5 place to put thermistor and in the list there is only 3? it miss me some ?
i have start welding and...
i have V1R1 power supply wich i have receive with my kit. But i have order exactly the list from Nelson in his file at first post and i see on this board there is 5 place to put thermistor and in the list there is only 3? it miss me some ?
See this post: https://www.diyaudio.com/community/threads/f5m-kit.408290/post-7663634
Yes, the revised board uses five thermistors.
Yes, the revised board uses five thermistors.
The board you have uses 3 + one on the AC line as seen in the schematic shown on page 5 of the F5m PDF in the first post of this thread.
Last edited:
it have been forget to be replaced in the list of nelson....
there is some other thing that it have been changed?
i have change the trimmer by these one below but i have been forced to bend the paws if i'm right....
there is some other thing that it have been changed?
i have change the trimmer by these one below but i have been forced to bend the paws if i'm right....
in your opinion all is ok?:
hello all,
i have to order missing thermistance wich were not indicated in the first list of Nelson, but i'm in europe and to order back from digikey a small order i have 20 euros for shipping...
i have find this : could it run instead ?
https://www.reichelt.com/fr/fr/ntc-...fvuurxSscltDusDbdB10avuzk_H23xDhoCUeMQAvD_BwE
there is some other parts wich are not on the first list that i have to order back?
i have to order missing thermistance wich were not indicated in the first list of Nelson, but i'm in europe and to order back from digikey a small order i have 20 euros for shipping...
i have find this : could it run instead ?
https://www.reichelt.com/fr/fr/ntc-...fvuurxSscltDusDbdB10avuzk_H23xDhoCUeMQAvD_BwE
there is some other parts wich are not on the first list that i have to order back?
Thanks, I kinda missed this, but yeah, they are cool amps.
One of them is a little tempermental, it likes to take out HT fuses about every 4th or 5th power on, and I can't figure out why. I think one of the tubes has an intermittent cathode-heater short or something...and I kinda wish they had smaller mains caps, the original mains caps (400v 3800uf) were sketchy, so I replaced them with caps that will fit, and they're much too big (4700uf). I had to add soft start circuits into the power cables to keep them from tripping the breaker at power up.
So yeah, they are pretty, but they're a bit of a pain in the ***, hehehe
Last edited:
I'm scrolling through this thread and didn't see the recommended transformer for the power supply. Anyone have that available. I've tried searching too, but came up short. Thanks.
It depends on your build but for the most part, if you get a 300va-400va Antek 18vac or 20vac secondaries, you should be all set. If you are building a pretty small amp, you can get away with a 200va.
https://www.antekinc.com/
https://www.antekinc.com/
Thanks, also found post 1808 with the info. https://www.diyaudio.com/community/threads/f5m-kit.408290/post-7737952
I just had a look at post no.1 of this thread and I agree with member @e_fortier -- recommended transformer(s) can be found there.