Mine generates negligible heat with any of the bias settings I tried, even with the silicone glued to the top. I measured with an IR thermo I use to test for transistor temps.
--Tom
I have noticed that distortion increases with usage, having done FFT and THD at various times. I suspect it is due to tube aging. Quite a bit of change if you measure at 1V in and 1V out or 1V in and 0.5V out; but a lot less of a change at lower V levels so it is not easily discernible to the ears.
nash
Guys need your help. This is the first preamp I've ever made I can not get rid of hum, maybe you can help. I use the big board (I bought from the forum member) that has Ubib regulator and I-selector on board. I tried grounding with and without lifting it with resistors/NTC thermistors, no luck. Moved the transformer far away, nothing. I know that user Marra uses same boards and he doesn't have any hum, and of course I tried his grounding configuration. My nutube is super microphonic and I just cant isolate it. I tried eraser, vibro isolation dynamat, neoprene, you name it. I see it was mentioned in #5739 that microphonic can cause humming as well. Maybe that's the problem. Here are some pictures of the board and the tube zoomed in.
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Does the hum go away when you touch the volume pot? It is not included in the picture so its hard to see how it is connected. You definitely need solid continuity between the pot's body and the rest of the circuit so there are no current return loops. You can also try out clipping leads onto different points and probing around and listening. You can also put your DVM into continuity mode and connecting to the input negative point and probing around between the negatives on the board and chassis to ensure there is solid connectivity (do this with the power off). Another thing to look at is your chassis construction. I see you built this in what looks like a modular chassis that has anodize coating. That is not very conductive. What you may want to do is sand off the points where the different panels touch to achieve more solid continuity.
If none of that works, please include some more (clear and well lit photos) and we can look some more.
--Tom
Member who made it (wengtech) says that he has built several and they work.
Here is one example by Marra: B1 with Korg Triode
Only difference I have is I am not populating I-selector part and feed the input directly to what would be the output pins of what supposed to be the alps pot pads. Or grounding those.
Then it could be the NuTube. Mine hummed until I applied that generous amount of silicone to the top. The microphics disappeared (audibly anyways) with 6L6's suggestion that is in the build guide of using an eraser taped to the top, but that did not eliminate the hum, so maybe you need to get more aggressive with the dampening on the tube?
--Tom
Yep, was poking everywhere with a wire creating all possible loops and arrangements just to hear any difference. All voltages are ok. I connected Jfets wring way first, but they measure fine now, so doubt that would be it. For me two big questions are:
1. If my particular tube is so microphonic, can that be some internal hum?
2. I do not have the schematic for the output delay relay, but based on the traces everything looks fine, I mean maybe that small psu for the relay GND should be somehow isolated, but used a couple of similar configurations in the past and did not have any troubles. Most confusing... Maybe most expansive 10uf wax/PIO caps will fix it haha, isn't it the audiophile way of troubleshooting?
The filament current is 17-18mA as Papa suggests. 250 vs 475R are due to lower filament psu 5V.
Got excited with that dirty soldering for a second, no g and that f pad are the same in the schematics and Papa's layout.
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Again G and F look like short..microphonic cure is in on the other side check build guide B1 with Korg Triode
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To my biggest embarrassment I do not have any measurement tools but multimeters . I can only measure the voltage and it is 23.8V stable. The PSU is just a different layout of Salas Ubib, that should be really good PSU. I had some difficulties with making the voltage stable at first, but then with Salas' help I manage to do so.
. I can only measure the voltage and it is 23.8V stable. The PSU is just a different layout of Salas Ubib, that should be really good PSU. I had some difficulties with making the voltage stable at first, but then with Salas' help I manage to do so.