Ok, i got brave and put a 5A slowblow in.....
I also plugged the amp into a kill-a-watt device to see how many amps it was pulling in.
Well, the fuse didnt blow for about a minute, thats when i turned off the switch, i was worried because i started to smell something... remember this is my first build and my first class A.
Upon inspection i found several components that were very hot..
The matched IRF9610`s, especially the one close to the speaker output.
Also the big resistors on the boards by the IRF240`s
Also the current inrush limiter was hot hot hot, which i read is normal.
I`m a bit scared and im not sure if this is normal or not.
The amp drew 6.2 amps and slowly climbed to 6.5, does that seem right?
Are there any measurements i can take to verify proper operation?
This is very exciting and scary at the same time, what a thrill!!!
😱 😀. 😕😀. 😀
source rsistors and irfp9610 will need some time to warm up. not in one min.
6L6
I could hardly keep my finger on the 9610, but i could keep my finger on the big resisters by the Irf240`s. The large heatsink didnt seem to get that hot, surprisingly. Should i put a little sink on the 9610`s?
Sakellogg
I agree! If i get this amp actually working it would be a miracle, im inviting the neighbourhood for free beer and music, it will be toasty.
I think the resisters are 5 watters, i mounted them well up from the pcb. They are the largest kind in the build. Where are the source resistors located? What is their value, i can find them that way.
Wow! This is a lot of fun! Im going to plug it back in tomorrow to measure dc offset. My wife is home now and i hate to blow a fuse and have her tell me i should pick a `safer` hobby...
Thanks for all your help!
I could hardly keep my finger on the 9610, but i could keep my finger on the big resisters by the Irf240`s. The large heatsink didnt seem to get that hot, surprisingly. Should i put a little sink on the 9610`s?
Sakellogg
I agree! If i get this amp actually working it would be a miracle, im inviting the neighbourhood for free beer and music, it will be toasty.
I think the resisters are 5 watters, i mounted them well up from the pcb. They are the largest kind in the build. Where are the source resistors located? What is their value, i can find them that way.
Wow! This is a lot of fun! Im going to plug it back in tomorrow to measure dc offset. My wife is home now and i hate to blow a fuse and have her tell me i should pick a `safer` hobby...
Thanks for all your help!
Oh yikes... now you all have me worried... i better go find a variac. Im sure at work they have one...
It truly did draw 6.5 amps...
It truly did draw 6.5 amps...
6.5ampsx115V=750W if there had been 2 channels🙂
are you sure your resistors are correct?
seems like you have a sky high bias.
are you sure your resistors are correct?
seems like you have a sky high bias.
Sky high bias I agree.
5 watt shouldn't get hot that quick! Mine ar 10 watt 1 ohm with almost a half a amp and they don't get warm.... Even playing music.
If I wher in your place I would unsolder one side of my resistors and make sure the values are correct.
Especaly around the mpsa's.
You will get it. don't give up. It will be worth it.
I left my meter in current mode once and mesured voltage drop across the source res in one channel of my aleph 1.2. 12 matched fets new meter later she was singing. Very well too.
5 watt shouldn't get hot that quick! Mine ar 10 watt 1 ohm with almost a half a amp and they don't get warm.... Even playing music.
If I wher in your place I would unsolder one side of my resistors and make sure the values are correct.
Especaly around the mpsa's.
You will get it. don't give up. It will be worth it.
I left my meter in current mode once and mesured voltage drop across the source res in one channel of my aleph 1.2. 12 matched fets new meter later she was singing. Very well too.
I think the resisters are 5 watters, i mounted them well up from the pcb. They are the largest kind in the build. Where are the source resistors located? What is their value, i can find them that way.
Sorry I missed that.
They are the ones that are the largest in size not ohms on the bias/outputs boards.
I forget what the value is in a aleph 2? Maybe 1.5 ohm?
Sorry I missed that.
They are the ones that are the largest in size not ohms on the bias/outputs boards.
I forget what the value is in a aleph 2? Maybe 1.5 ohm?
Yes, don't take what I'm saying as a instead of a variac. You can test these things while useing a variac. Just have to scale down what you expect to get accordingly.
These guys have forgot more stuff than ill know.
Just adding my 2 cents. Only worth 1c.
Could you tell me which resistors control bias? I have 1 ohm resistors that are large and connected to the IRF240 and i think the source resistors are small and red, red, brown, black, brown, i have to look it up but they are 0.6watt and supposed to be 221 ohm. If i use the multi meter in the 2k setting i measure around 219, which should be right....
Is this helpful?
Im going to follow the advice and get a variac first...🙂 😎
Is this helpful?
Im going to follow the advice and get a variac first...🙂 😎
The 1 ohm are the source res.
The 221 are the gate resistors.
119 is fine.
If you have a scematic the bias resistors are around the top mpsa18
There are 2 mpsa18. The one with more resistors around it sets/ajusts the bias.
You check the bias by mesuring the voltage drop across the 1 ohm sourse resistors.
If you read .5 vdc you have .5 amp. E over I/R
But don't fire it up without a virac. You can check the values of the res.
Just remember if you don't undo one side it will mess up your reading.
You could read a close value of 221 because it goes to the gate of the fets
The 221 are the gate resistors.
119 is fine.
If you have a scematic the bias resistors are around the top mpsa18
There are 2 mpsa18. The one with more resistors around it sets/ajusts the bias.
You check the bias by mesuring the voltage drop across the 1 ohm sourse resistors.
If you read .5 vdc you have .5 amp. E over I/R
But don't fire it up without a virac. You can check the values of the res.
Just remember if you don't undo one side it will mess up your reading.
You could read a close value of 221 because it goes to the gate of the fets
Ahhhh that explains a lot! Thank you very much. I will check it in the morning by looking at it.
I know where the mpsa18 are located, i will check the schematic and my board.
I know where the mpsa18 are located, i will check the schematic and my board.
witch chematic do you use? papa's or K-K?
or what?
i have papa's. and have builds k-K's
or what?
i have papa's. and have builds k-K's
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I use Kristians schematic. It calls for -only- 8 times 10,000uF in caps. I think his current schematic may be updated..
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