A crude drawing of a simple DBT lifted from the thread link shown.
In the UK the Live feed is of course Blue, not Black.
dim bulb tester, "schematic"
In the UK the Live feed is of course Blue, not Black.
dim bulb tester, "schematic"
Attachments
Last edited:
Hi again,
Haven't had time to get working with the amp again until now. I have fitted the replacement transistor to the heatsink and applied new cooling paste + mica pad in between. I will solder it back in a moment, and then test the machine with the DBT.
So the procedure should go something like ;
1. Starting up the NAD with the bias set to maximum resistance through the DBT
2. Adjusting the bias to minimum resistance on respective channel while observing the DBT?
So, I just wonder, am I supposed to turn bias all the way when testing for each channel?
Best,
A
Haven't had time to get working with the amp again until now. I have fitted the replacement transistor to the heatsink and applied new cooling paste + mica pad in between. I will solder it back in a moment, and then test the machine with the DBT.
So the procedure should go something like ;
1. Starting up the NAD with the bias set to maximum resistance through the DBT
2. Adjusting the bias to minimum resistance on respective channel while observing the DBT?
So, I just wonder, am I supposed to turn bias all the way when testing for each channel?
Best,
A
Starting on max resistance looks correct (I'm just looking at an online circuit for the amp).
Have both channels set like that.
As you turn the preset the bias current should increase and the bulb will glow more. If both channels seem OK (bias adjusts and there is no DC offset at the speaker terminals) then you should adjust the bias carefully according to the service manual and then recheck the bias again when on full mains.
Have NO speakers attached while testing.
Have both channels set like that.
As you turn the preset the bias current should increase and the bulb will glow more. If both channels seem OK (bias adjusts and there is no DC offset at the speaker terminals) then you should adjust the bias carefully according to the service manual and then recheck the bias again when on full mains.
Have NO speakers attached while testing.
YES - they are working! I am so relieved right now.
I started them up through DBT and got the first bright light during the initial power surge, quickly followed by a slight glow (just like I had hoped it would look).
Checked and tested the bias presets, got them as good as I could, then tweaked the offsets as close as possible. When I had left it for a good 30 minutes and no problems, I plugged it to full voltage and voila! No blown fuses, and starting up just as normal.
The only thing I noticed is that I can't get neither the bias or the DC offset values to stay perfectly still, they seem to be slowly oscillating up and down with 0.2-0.8 mV. It's the same for both channels and I'm guessing this is normal and would not pose much of a problem.
Now playing sweet music again, I am so happy I got it up and running. Kudos for being patient with my limited knowledge of these things Mooly, and thanks for making me put together the dim bulb tester. It will probably come in handy on more occasions, this habit of buying vintage gear is probably not gonna stop anytime soon
I started them up through DBT and got the first bright light during the initial power surge, quickly followed by a slight glow (just like I had hoped it would look).
Checked and tested the bias presets, got them as good as I could, then tweaked the offsets as close as possible. When I had left it for a good 30 minutes and no problems, I plugged it to full voltage and voila! No blown fuses, and starting up just as normal.
The only thing I noticed is that I can't get neither the bias or the DC offset values to stay perfectly still, they seem to be slowly oscillating up and down with 0.2-0.8 mV. It's the same for both channels and I'm guessing this is normal and would not pose much of a problem.
Now playing sweet music again, I am so happy I got it up and running. Kudos for being patient with my limited knowledge of these things Mooly, and thanks for making me put together the dim bulb tester. It will probably come in handy on more occasions, this habit of buying vintage gear is probably not gonna stop anytime soon
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.