Several points:
From Jim McShane (an excellent tube dealer) on AA:
"Do yourself a favor - clean the tube pins and sockets every time you change tubes. A bottle of DeOxit D5 and a handful of good old fashioned pipe cleaners works great for octals and other large pin sockets; for the miniatures, D5 and the little tiny dental brushes for cleaning between your teeth (another drug store item) do a solid job. BTW, D5 is good to 400F - so don’t lose sleep over it because of something you read on the "Hi-Fi Hysteria" forum. And it doesn’t gum up either. Spray some in a paper cup and let it evaporate - you’ll be able to see for yourself.
Sometimes you swap a tube and the new tube is okay. so the tube you removed must be bad, right? NO! Sometimes the scraping action of removing and reinstalling a tube in that socket is enough to temporarily restore contact - and fool you into thinking you have a bad tube! KEEP YOUR SOCKETS CLEAN!!"
Alcohol really isn’t enough to clean with. Old tube pins also often really need to be scrapped. A dental brush can work but sometimes I use a small Exacto knife. You’d be surprised what occasionally comes off.
On the other hand, I’ve tried more than half a dozen NOS Mullards (purchased from several sources) in the pre-amp section of my Cronus Magnum (which takes just one pre-amp tube) and all have started to get noisy within a month or so. Various short plates, long plates, 12AU7s, CV4003s, from various factories; it hasn’t mattered.
I also tried NOS Amperex and Radiotechnique (both, like the Mullards, made by Philips). The Amperex also started to get noisy: the RT (platinum grade from Upscale Audio: several over several years) have stayed quiet. Some of the Mullard CV4003s were Platinum Plus ("CJ Test") grade tubes from Upscale. Supposed to stay quiet in hard on tube pre-amps from the likes of CJ, Rogue and Sonic Frontiers. They didn’t. I don’t blame Kevin. I’ve just come to the conclusion that the Cronus and NOS Mullard are incompatible: I don’t know why. They certainly work in other pre-amps owned by many people. (For the record, NOS RCA/Raytheon 12AU7 black-plates and RCA/GE 5814s also stay quiet).
In addition, I’ve purchased tubes from Alfred Kayser and found him knowledgeable and fair. The very short plate CV4003s he sold me also started to get noisy in the Cronus pre-amp slot - but they took longer than even the Upscale Platinum Plus. Luckily the 12AU7 driver section of the Cronus has a significant effect on the sound and all of the Mullards that didn’t make it in the pre-amp slot went to the former section over time and sound(ed) great there. I also bought several NOS Mullard rectifiers from Alfred (back when I had gear that took them; mostly Modwright) and they all performed perfectly.
From Jim McShane (an excellent tube dealer) on AA:
"Do yourself a favor - clean the tube pins and sockets every time you change tubes. A bottle of DeOxit D5 and a handful of good old fashioned pipe cleaners works great for octals and other large pin sockets; for the miniatures, D5 and the little tiny dental brushes for cleaning between your teeth (another drug store item) do a solid job. BTW, D5 is good to 400F - so don’t lose sleep over it because of something you read on the "Hi-Fi Hysteria" forum. And it doesn’t gum up either. Spray some in a paper cup and let it evaporate - you’ll be able to see for yourself.
Sometimes you swap a tube and the new tube is okay. so the tube you removed must be bad, right? NO! Sometimes the scraping action of removing and reinstalling a tube in that socket is enough to temporarily restore contact - and fool you into thinking you have a bad tube! KEEP YOUR SOCKETS CLEAN!!"
Alcohol really isn’t enough to clean with. Old tube pins also often really need to be scrapped. A dental brush can work but sometimes I use a small Exacto knife. You’d be surprised what occasionally comes off.
On the other hand, I’ve tried more than half a dozen NOS Mullards (purchased from several sources) in the pre-amp section of my Cronus Magnum (which takes just one pre-amp tube) and all have started to get noisy within a month or so. Various short plates, long plates, 12AU7s, CV4003s, from various factories; it hasn’t mattered.
I also tried NOS Amperex and Radiotechnique (both, like the Mullards, made by Philips). The Amperex also started to get noisy: the RT (platinum grade from Upscale Audio: several over several years) have stayed quiet. Some of the Mullard CV4003s were Platinum Plus ("CJ Test") grade tubes from Upscale. Supposed to stay quiet in hard on tube pre-amps from the likes of CJ, Rogue and Sonic Frontiers. They didn’t. I don’t blame Kevin. I’ve just come to the conclusion that the Cronus and NOS Mullard are incompatible: I don’t know why. They certainly work in other pre-amps owned by many people. (For the record, NOS RCA/Raytheon 12AU7 black-plates and RCA/GE 5814s also stay quiet).
In addition, I’ve purchased tubes from Alfred Kayser and found him knowledgeable and fair. The very short plate CV4003s he sold me also started to get noisy in the Cronus pre-amp slot - but they took longer than even the Upscale Platinum Plus. Luckily the 12AU7 driver section of the Cronus has a significant effect on the sound and all of the Mullards that didn’t make it in the pre-amp slot went to the former section over time and sound(ed) great there. I also bought several NOS Mullard rectifiers from Alfred (back when I had gear that took them; mostly Modwright) and they all performed perfectly.