Grading & Matching
Small Signal Tubes
In order to sell "selected" tubes, you have to have tubes to select from. If you check most websites, they only have 3-5 pieces of one tube in stock. If you are only picking from five tubes, the chance of you getting super bitchin' ones is not so great.
Most small signal and preamp tubes you buy at Upscale Audio will have individual test results. First, each tube is heated up and cooled down in a specific manner to see if the tube will shift internally and become microphonic. Next, each tube is tested for shorts and grid leakage.
After this test, the tube is listened to with high-quality Sennheiser headphones in a circuit that simulates a phonostage. In other words, real-world voltages and high amounts of gain. This lets us hear any noise that might be present in a tube, as well as grading the level of microphonics present. For a deeper discussion on the ins and outs of microphony click here.
After passing muster for noise and microphony, each tube is tested individually for triode balance. Once this process is complete, tubes are then matched and sorted into three different grades:
Driver / Buffer grade -
Note: There is nothing wrong with these tubes in many applications and they are an opportunity for you to save money!
The tubes that are low in noise, but not lowest in microphony. There are some tubes that will never be low in microphonics... this is by design. Usually these tubes are used in a circuit where they don't need to be low in microphony, such as the driver stage of an amplifier, or an output buffer in a DAC or CD player. In these circuits, purchasing a low microphony tube will not yield any performance benefits, so take advantage of the lower price, and take your sweety out for a nice meal.
Please note that with some tubes types, almost 90% will be this grade. Count on us to walk you through and get you the right stuff.
Gold - This is a tube that is low in microphony and has excellent noise and triode balance measurements. Typically triode balance for Gold Graded tubes will be between 15% and 20%, but may be higher depending on available stock. Perfect for preamps, phono stages, and the input stage of power amplifiers. It can't get much better, unless you go to Platinum Grade or Kevin's Stash.
Platinum - Sometimes you just want the cream of the crop... Whether it's personal preference or a difficult circuit, our customers demand the absolute best. So for this customer, we offer Platinum grade. The difference between Gold Grade and Platinum Grade is a measurable difference in triode balance. Small signal tubes such as 6922, 12AX7, 12AT7, and others are like two tubes in one glass envelope. That is why they are called "Dual Triode." Triode balance in Platinum Graded tubes is typically 10% or tighter, but may be higher depending on available stocks. They will also measure at the tippy top for transconductance.
Kevin's Stash - Better than cream of the crop (Platinum), Kevin's Stash is the ultimate. In preamps and amps, the most important tube is the gain tube, and that’s why we test them not just electrically but BY EAR using headphones. After each testing session, Kevin selects the best of the best for Kevin's Stash. These are the tubes that the Tube Dude himself historically stashed away for his private use. Believe it or not, selling tubes is not a profit center for Upscale Audio. The man-hours invested in testing each individual tube is ridiculous. Nobody else tests like this. Nobody else would. We do it simply because Kevin loves tubes. Kevin's Stash is the ultimate grade for those who understand that tubes are the amplifying device and are the beginning and the end of their audio system. After all, sonic detail is what high-end is about.
Will you hear a difference? Maybe not. But if you have a lot of jack invested in your system it may be worthwhile to you. Plus, there are certain products that demand tight tolerances. Trust Upscale Audio to get you the best stuff to suit your needs.
DC Balancing & Custom Testing - Some products, like Music Reference power amps, and a couple VTL preamps, require that the front end tubes be DC balanced. We can do this for you at a nominal extra charge of $10 per tube. It takes a long time for us to do this and the $10 charge is a gift.