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GB B1 Nutube PCB with integrated PS

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avtech

avtech

Member
Joined 2017
Was this photo taken before the nutube was installed?

Have a look at the nutube footprint - there is nothing connected to the lower track connections.

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avtech

avtech

Member
Joined 2017
That's actually a good thing as we have isolated most of the circuit.

Remove R203 and 207 also if you didn't already and check for the 9v at R4 (+R).

Then if still no stable power supply, remove R4 and look for 23v/22v on R3 (WRT GND).

If it is stable, then the fault is between R4 and the LED.
If not stable, the fault is further back so remove R3 and look for 23.4/22.8v on R2 (WRT GND).

Make sure you have a printed schematic (the V1.3) and mark off what you find as you go.

You'll get there soon!
 
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WKCox

WKCox

Member
Joined 2004
Finally got around to finishing the PC board and had to quickly give it a test run before installing it into a case. Powered right up perfectly. Set bias to 10V and I'm now listening to wonderful music.

Thank you Sylvain for designing this unique board and for the group buy. Thank you JeffreyJuice for the JFETs. And finally, thank you Nelson for sharing your exceptional creations with the DIY Greedy Boyz.
 

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avtech

avtech

Member
Joined 2017
Please confirm your results for the following:

R103 & R107 removed, R203 & R207 connected:

R103 & R107 Connected, R203 & R207 removed:


9.4v is a touch high:

Nelson Pass said:
...Also, the tolerance here on the zener is about 9.0 to 9.2V

If you are not within that, consider adjusting the resistors in series with the Cathodes.
Click to expand...

Best to match the Zeners to 9.1v if possible. I tested a batch of 10 zeners and chose the pair closest matching 9.1v.
 
avtech

avtech

Member
Joined 2017
Marra said:
With R203/R207 I have 8.5V at the diodes all other voltages fluctuate but are 3V down.
Click to expand...

You meant with R203/R207 removed, R103, R107 connected? Sorry, I misread your post.

Marra said:
With things as you suggested the voltage fluctuates but settles at 24.04V and the LED lights up.
Click to expand...

This suggests an issue on the #1 side of the circuit as you get a settled voltage with the left side (R103/7) out of circuit. Mine takes a while to settle also, presumably as the triode warms up.

This time with just R103/107 connected (R203/7 out) and getting the reported 3V drop at the 24V, take R4 out of the circuit and see if the 24V stabilises (R4 will cut the 9V side of the circuit). This should tell you if it is heater side or buffer side.

If no change, put R4 back in, take R103 or R107 out of circuit. This will then hopefully identify if it is the input or output side of the tube that is the problem.

I can't remember if I asked, but where did you source your JFETs from?
 
M

Marra

Member
Joined 2009
Paid Member
Sorry I should have said the readings are without the Nutube in place. I will try what you suggest. Should I solder the tube back in place?
The jfets were sourced from Spencer of Fet Audio some years ago and matched by me. Your advice is much appreciated.
 
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