I ran thru some issues with my pre amp and ended up having to send back to the manufacturer for repair. I have only used tested tubes from Tube Depot with the unit. All have been tested for microphonics and matched. The unit is the new pre from Musical Paradise and can run multiple versions of 6 V and 12V tubes. I put up a brief review when I received the unit in this circle.
The result of the diagnosis is “ The grid of that tube is short to either plate, cathode or filament, so a high voltage leaks to the grid causing these damages.”
I have owned tube equipment for 20 years and never run into this. I have purchased high $$ NOS from Upscale all the way to sketchy tubes from Russia / Ukraine from EBay.
I have never run into a faulty tube damaging a piece of gear. Fuses blow, tubes have cracked, gone grey, etc. but never caused the damage above which resulted in a blow resistor as well as requiring the volume pot to be replaced.
Can a bad tube cause these damages and how in the world do I know it’s a bad tube? No overheating, nothing as I described above.
Curious to what people can provide and thanks -
Thanks for inform us on this disaster you have suffered.
Seems they dont fully test the tubes they sell, only microphonics and emission what are need to match tubes are not tremendously useful.
Can a bad tube cause these damages and how in the world do I know it’s a bad tube? No overheating, nothing as I described above.Yes a shorted tube on the fly can take several components to destruction if the short is big or if not brief. The tube broker have to test the tube for shorts with a analog or digital meter or preferably a proper tube tester with the tube hot(in use), DMM tests with the tube cold are not fully realistic.
A microphonics test is a quick procedure and the emission test to match tubes also:
https://www.youtube.com/watch?v=13n1VCR6UXwAlso your ears can evaluate if a tube is microphonic along other empirical tests, so they are doing nothing extraordinary.
https://www.youtube.com/watch?v=XNoJXpzIsFgThis seller was very clear
>>They tested only microphonics and a emission to match, they have not tested your tube for short circuit as you came to know, neither did the heating to activate the getter to clear gases that build up with valve inactivity, activate the getter can take many hours of electricity expenditure and many defective tubes do not withstand many hours of heating to activate the getter to clean the gases and go shorts and destroy themselves so this represents a cash loss and they have to buy a proper heater equipment and a skilled technician on the payroll as Upscale or Andy have, they prefer made the custumer amp test pilot, they even can blame the faulty tube to Fedex.
It is important to note that if a tube has a lot of gas inside, whether it is air or gas from vaporized metallic elements, this cloud inside the valve can create a short circuit when tube is in use, which is why the heating for many hours to activate the getter is so important, after the getter activation the tube still has to be verified in what condition the valve is now in relation to vacuum and shorts.
