Hello
My name is Alessio, I write from Italy, I apologize in advance for my basic English but luckily there is google translate 🙂.
I hope someone can help me or give some advice. I'm building an aleph 3 to measure the 5V reference voltage on R120 I had to increase the R113 resistor to 150K
Do you think this is normal? Can I perform some checks before continuing with the construction? do i have to check the hfe of the mpsa18?
My name is Alessio, I write from Italy, I apologize in advance for my basic English but luckily there is google translate 🙂.
I hope someone can help me or give some advice. I'm building an aleph 3 to measure the 5V reference voltage on R120 I had to increase the R113 resistor to 150K
Do you think this is normal? Can I perform some checks before continuing with the construction? do i have to check the hfe of the mpsa18?
You should be measuring about one-half of a volt (0.5 volts) across R120. Did you read the ".5V" on the schematic as "five volts" instead?
yes writing error, I should have 0.5 V instead I measure 0.35 V and to get to 0.5 I had to put 150K on R113. Does 150K seem anomalous to me or can this be correct?
Yes, it should be 0.5VDC. That bias current is way too high. Change R113 back to the proper schematic value.
Also check R120 to make sure it is still 0.47 ohms, and has not been damaged by overheating.
Also check R120 to make sure it is still 0.47 ohms, and has not been damaged by overheating.
if Pass wrote 500mV across 0R47, leave it at it
2A Iq with 23 to 25Vdc rails is adequate for Aleph 3
2A Iq with 23 to 25Vdc rails is adequate for Aleph 3
The problem is that if I remove the resistance from 150K R113 the voltage does not reach 0.5 but 0.35
Are your rail voltages much higher than 25V? Higher rails will give you a lower bias current and voltage across R120.
Also, verify that R111 and R112 are 1.5K and R113 is 47K, like on the schematic.
Also, verify that R111 and R112 are 1.5K and R113 is 47K, like on the schematic.
goal is to have 500mV there
you got it adjusting value of R113
so, all done
there is no reason to worry - if everything else is by the book
R113 is there, exactly serving that function - to get desired Iq
difference to Factory schematic is that you have mosfets and bjts slightly different than ones used in PL, in moment of producing that schematic
so, again, all good
Rayma
Aleph 3 is declared as 30W amp, 25Vdc rails, sucking 150W from wall, most of it being heat at heatsinks
with measly 25W of heat per mosfet, what's problem?
Yes the voltage is higher about 28 volts, so it may be due to the higher voltage that's interesting R111 r111 are correct, I increased r113 to 150K to get 0.5v on r120..
I thought it was anomalous to have such a high value of r113 of 150K, but if you tell me that it can be corrected with a value of this type, I continue my tests with this value of r113