Heatsink question

I still think Malvino is one of the very best book. I since lost my original book, I actually tried to buy another one few years ago and mistakenly bought the lab book. I am still going to buy one one day just for sentimental reason that it's the one that got me into my career. It's about the easiest book to read, I learn transistor with this book. Of cause I since studied a lot more advance books like the Integrated circuit by Grey and Mayer, Microwave Engineering by D Cheng etc. But Malvino still to me is the best and the material can go very far into design transistor circuits. Hell, if you study Malvino, then get the Power amp design book by Bob Cordell, you'll be very good in audio circuits.

I did a search for both books on the web. Electronic Principles 7th and 8th edition by Albert Malvino are available as free PDF's here

Bob Cordell's Designing Audio Power Amplifies must be paid for. If you want it as a paperback you will pay through the nose, $200 at Mcgraw Hill and over 300 on Amazon. I consider that crazy. I did find it as an E book here on Barnes and Noble for a much more reasonable $40.

Just thought I'd add that for anyone looking for them.

Shelly_D
 
Yes so far everything has been pretty close.

I believe we are making great progress. The measurements are now all in range of the good board!

A +1.34V
B +. 745V
C -. 543V
D - 1.147V
E - 1.15V
F +44mv
G 1.342V

R33 +1.6V
R32 - 1.3V

Parts i replaced before test was Q4 and CR24
 
I did a search for both books on the web. Electronic Principles 7th and 8th edition by Albert Malvino are available as free PDF's here

Bob Cordell's Designing Audio Power Amplifies must be paid for. If you want it as a paperback you will pay through the nose, $200 at Mcgraw Hill and over 300 on Amazon. I consider that crazy. I did find it as an E book here on Barnes and Noble for a much more reasonable $40.

Just thought I'd add that for anyone looking for them.

Shelly_D
Cool thanks! One of those downloads was dead but I'll dig around. Nice find!
 
I did a search for both books on the web. Electronic Principles 7th and 8th edition by Albert Malvino are available as free PDF's here

Bob Cordell's Designing Audio Power Amplifies must be paid for. If you want it as a paperback you will pay through the nose, $200 at Mcgraw Hill and over 300 on Amazon. I consider that crazy. I did find it as an E book here on Barnes and Noble for a much more reasonable $40.

Just thought I'd add that for anyone looking for them.

Shelly_D
I don't know why the Cordell book is so expensive. I bought mine used CHEAP!!!! It was cheap only a few months ago.
 
Yes so far everything has been pretty close.

I believe we are making great progress. The measurements are now all in range of the good board!

A +1.34V
B +. 745V
C -. 543V
D - 1.147V
E - 1.15V
F +44mv
G 1.342V

R33 +1.6V
R32 - 1.3V

Parts i replaced before test was Q4 and CR24

Are these reading after you change Q4 on the bad board?

There is some offset as A and D are not balanced.

I want you to measure the voltages on these

Urei troubleshoot 1.JPG
 
Are these reading after you change Q4 on the bad board?

There is some offset as A and D are not balanced.

I want you to measure the voltages on these

View attachment 1006890

Not sure what you mean, what is offset exactly?

Measurements as per your last image. First is bad board, after comma is good board.

F 0mv (both boards)
G - 2mv bad, 0mv good
E 97.6mv bad, 30.4mv good
C +. 971V, +. 9V
B +1.44v
D +.649v,, .+87v
A +. 74 , +. 67

Looks like power trans going in soon right?? :)

Both have vr36 full CCW
 
Look like both boards are ok now!!! I assume point B of both boards are 1.44V. It's low, it should be about 2.4 to 2.7V.

Let me verify, on the bad board, you have everything except Q15 and 16.

Make sure you have the DIME BULB test set up. I think you are ready to put in the big transistors.

Did you buy the 0.39ohm big resistors?
 
Look like both boards are ok now!!! I assume point B of both boards are 1.44V. It's low, it should be about 2.4 to 2.7V.

Let me verify, on the bad board, you have everything except Q15 and 16.

Make sure you have the DIME BULB test set up. I think you are ready to put in the big transistors.

Did you buy the 0.39ohm big resistors?

I have new resistors but I did not buy the correct wattage. I believe it's supposed to be 5 watts and I bought 1 watt metal film
 
No, read back the old posts how I arrived the value, this is a design after I had you test how hot the amp gets with increased bias. Remember I mentioned about the Oliver's condition that you want to have about 22mV to 26mV across the big resistor to get the minimal crossover distortion. The value of this resistor is very important. The original 0.3ohm is a little too low.

Now if you are willing to have a fan blowing on the heatsink all the time, you can use lower value like 0.33ohm and increase the bias current.

You can use the 0.5ohm, then adjust to lower current to achieve Oliver's condition, but that will kind of half way defeating the effort in adding one extra pair of transistors.

this is something you need to know about Oliver's condition if you are getting into power amp circuits.
 
You follow how I calculate out all the voltages? Do one by yourself, this will help you understand the amp a lot more and you might not need my help. It's not that hard, just 10 minutes investment of your time at the beginning. It will save your pcb and time later.
 
0.39 without fan, 0.33 with permanent fan.

Well the ones on there now are original. They took some abuse during the previous smoke. Do you think I should swap them out for the .47 to test or leave them there? My dim bulb is ready

--

I only flowed it slightly, i have to get into it calculating the voltages.. Its been great learning experience! Will spend more time learning it
 
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