no doubt.nightscope wrote:David Bock, who designed the mic, advised me that in his experience about half of this particular type were good enough. The original tube is still going strong but I will get a bunch to avoid disappointment.
buying from a good supplier helps. good companies test the tubes for low noise and microphonics and sort according to gain. they also warrant the product for at least 6 months.
here in this part of America, we use Ruby tubes, but Electro Harmonix and Groove Tubes also screen for bad tubes before screening on their logo. product from these guys is pretty consistent. i'm sure someone does the same in the UK and Europe.
i never deal with electronics store tubes or no name product, so i see fewer unusable tubes. naturally, just because they are so variable, if one has the budget, buying a hundred to choose two has always been good practice.
anyway, if it's 12ax7's, i wouldn't worry about them being available. if you have a good supplier, you won't see many bad ones. soundelux certainly got bulk tubes and tested for themselves. a good supplier would test before shipping.