Hi guys, I'm writing to speak about a weird issue I'm experiencing with my last build of B1 Nutube. I noticed that when I put the 50kohms volume pot to max position, the lights of the triode tend to dim and to blink a bit and when I lower the pot they return stable. I have to say that when building I made a mistake: I cut the leads of the small caps too long, so they touched the metal plate underneath (indeed the pre didn't sound at all, even showing correct values at all check points). When I got aware of the mistake, I cut immediately the excess of the caps leads and the board then started to sing. But it now shows this strange behaviour: Could have I damaged it somehow? The caps are Clarity Caps 3.9 uF out, 1 uF middle, 330 nF in.
Thanks in advance.
Gaetano.
Thanks in advance.
Gaetano.
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Perhaps your capacitors are damaged.
Are you still getting correct voltages? Do the voltages at T7, T8, G1, G2 vary when you set the volume pot to maximum and the Nutube dims and blinks? What are these voltages now?
Did you have a source connected to the input when this was happening, or did you short the input, or was there nothing connected to the input?
Are you still getting correct voltages? Do the voltages at T7, T8, G1, G2 vary when you set the volume pot to maximum and the Nutube dims and blinks? What are these voltages now?
Did you have a source connected to the input when this was happening, or did you short the input, or was there nothing connected to the input?
Aree you saying that given that I shorted them, they could have been damaged? Even if they are 630v rated? How can I check if they are really damaged?
Gae
no way that these caps are damaged
in fact, hardly any cap in that circuit can be damaged, except polarized ones being soldered backwards
in fact, hardly any cap in that circuit can be damaged, except polarized ones being soldered backwards
Glad to hear this, but at this point what else could be the reason for the Nutube to dim and blink that way at max volume?
Hello all. I've hit my frustration point with my kit. When I checked my voltages they were all good, except T7. I can get T8 to 9.50 VDC, but the lowest I can get T7 is 17.61 VDC. I've been reading this thread and I have reflowed all of the solder joints, but with no change. I've attached pics of the board. Any advice would be greatly appreciated
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Check the resistor at the 332k location as it does not seem to be the correct value.
I just had another look. Resistors need swapping.
I just had another look. Resistors need swapping.
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I'll be darned. It's amazing how much you try to double-check stuff and still make a mistake. Thanks so much for your eagle eyes! I won't get to it for a couple of days, but I'll let you know how it turns out.
Once again thanks for your help. It's greatly appreciated. 🙂
Thanks for the helpful advice. The funny thing is, I did measure and then put the resistors in the wrong place anyway. 🙄 It's those darn decimal points! To err is human I guess.
Seconded. It's the best advice about building these things I've ever been given. Not only is it a good way to double check things, but it's not impossible to get a part that's really out of spec, or damaged. Checking the basics can save real headaches later.
Hello All. I was able to switch the resistors and after keeping it on for a couple of hours T7 and T8 are stable at 9.50 VDC. Thanks so much, Ben Mah for finding my mistake. Thanks, Mark Johnson, rikiheck, and Mr. Pass for your help and encouragement. I'll be putting it in my system soon. I'll let you know how it sounds. 🙂
I am going to use one of these as a fixed-level buffer in front of an equalization network, and want it to be a fixed 10dB gain. Do we know the exact gain of this thing? Papa says it's a bit more than the 10dB he wanted, but doesn't seem to say what it actually is. So the basic question is: How much fixed attenuation do I need to put where the volume pot would otherwise go to get it down to 10dB?
What prevents you from measuring it yourself?
What prevents you from offering some kind of thank-you reward, to a member who measures it for you?
What prevents you from offering some kind of thank-you reward, to a member who measures it for you?