Eli Duttman wrote on 01/18/08 at 01:49:45:Steve,
I hate to be a party pooper, but a cautionary note is in order. Russian and Chinese 5U4Gs can be "problem children". Many times, I've helped 'philes with arcing 5U4G rectifiers. The solution has always been to use a US made NOS 5U4GB. Obviously, you have to use tubes that are in current production. New Sensor sells a Saratov, Russia, made 5U4GB, labeled EH. Feedback on the EH 5U4GB is anything but plentiful. It might be a good idea to check the Russian 'GB out for both reliability and sonics.
Eli,
The problem no longer seems to be limited to the 5U4G. In the past year I've had more bad 5Y3GT's (Sovtek) than in the 10 years prior. But, let's put it in perspective... Of the last 500 amplifiers that I've sent out the door with 5U4's I've only had to replace a dozen rectifiers under warranty.
I use the Chinese 5U4's because even though the Russian 5U4's look like a far better built tube, I found the way they made my amps sound to be less than acceptable. I find the Chinese 5U4's to sound the closest to a NOS G.E. which is my reference.
Now, I'm not a big fan of Chinese tubes (or anything Chinese for that matter) but in fairness they have come a long way since I got into this business. I buy all my 5U4's from RUBY. They sell both "no frills" tubes that basically means little if any grading and they sell Select grade tubes that they put their brand on. I pay over 3 times the price to purchase his Select grade tubes vs. bulk tubes from China. I let him weed out the bad ones.
And frankly, that is the game with all tubes, even NOS, in that there are good ones and bad ones in every batch. The guys with good tubes for sale are the ones who have taken the time to weed out the bad ones. 10% of all the tubes I buy - regardless of who their from - end up in the garbage can. I don't even try to send them back - too much trouble. I just look at it as overhead.
One of the biggest causes of tube failure in our case is from the tubes being beat to death during shipping to the customer. When you pack tubes with a 15 ~ 40 pound amplifier, the G-Force the tube experiences is based on the mass and weight of the amplifier. If the tubes were shipped by themselves in a separate box, the G-Force would be perhaps 100 times less. This is of course a double edge sword. But, I look at it as the final test. If the tube still works when it arrives with an amplifier, it definitely had no undiscovered weaknesses. If the shipping aggravated the tubes integrity, it will act up within days of going into service at which point we will replace it. When we send out a replacement tube, it is shipped by itself, without the equivalent of a boat anchor attached to it, so it almost always works.
So as for which tube to use in the new SE84C, I will make the decision based on how I want the amp to sound and how the amp looks with either tube. Of course, it will still be possible (as it has always been with our amps) to get away with using a 5Y3GT, 5AR4 or 5U4 in any of the amps without harming the sound or the amp. [smiley=tunes29.gif]
Steve