B1 with Korg Triode

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#8,644
Last night after posting that the new Nutube didn't fix my left channel, I started poking around the circuit board jiggling all the components to make sure that nothing is loose. I did not find anything loose, but when I turn it back on the left channel also lit up. I hooked my amp and CD player and it played fine.
This morning I turned it back on again and it is fine. Both channels are lit up and it is playing normally.

Now, should I just pull out the board and resolder all the joints again?

Thanks again for the help...
 
#8,648
I’ve had a failure in one side of the Nutube 6P1. The B1 w/ Korg has worked fine for years, then nothing on the one channel after startup. I pulled the board, and other than the one filament not glowing everything looks fine. I have the board connected to a lab supply and I have taken voltage measurements at T1-8. I also took resistance measurements at the tube pins. I’ve order a new 6P1 from the store, but need to be sure it’s safe to just solder in place. My brother has been using this preamp for the past couple years and it has NOT been left on 24/7. Measurements are attached as well as a pic of the board. Thanks for your help! Please take note of the voltage at T-6 and T8, and the resistance at pin F3.

Trim pots were set to halfway point for voltage measurements.

IMG_5747.jpegIMG_5748.jpeg
 
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#8,649
The power supply voltages are in the ballpark. 9.5V at T4 is within tolerance but a bit high. That is the filament supply voltage so a bit high does stress the filament a bit. However the left channel filament voltage T5 at 0.68V is within specification (Korg specified Min 0.6V Typ 0.7V Max 0.8V).

The rest of the voltages indicate a filament issue with the right channel of the Nutube. There was no measured current through it. However the filament resistance measured 471 Ohm, not infinite resistance. Does the right channel filament appear broken (discontinuous)? If so then it is no good. Do the solder joints look good? Try redoing the right channel filament solder joints. If that does not have any effect, then the filament is probably toast, and replacement is needed.

So the voltages appear within specification and installation of a new Nutube should be ok. Since you have a lab power supply, use it to bring the voltage up while monitoring the voltage at T5 and T6, which should not go higher than 0.8V (0.6V to 0.7V preferred).

According Korg, the Nutube service life is 30,000 hours.
 
#8,658
that's directly heated tube, where heater is also serving as Cathode

so, if filament is broken, no heated Cathode and no electron emission

if one wants to prolong puny tube life, counting on all Luck in Universe that is enough, go back few pages and find what we concocted to get precise heater voltage/current and to get it soft at startup

and with that implemented, do not forget to keep windows closed and also do not breathe while listening the music

:devilr:
 
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#8,660
Dear All,
I built this preamp some time ago and now the question arises as to whether it could also be used as a balanced pre, i.e. 1 board per channel? Is there anything that speaks against it, is there any experience? Thank you in advance!
 
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