The Electro Harmonix KT90-EH tube is a drop-in for any KT88 or 6550 tube... bias your amp just as you would a KT88 and you're good to go! Sonically they are true to the Electo Harmonix brand; clear top end that is open but not bright or tizzy, tight bottom end, and a clear midrange that is not hard or clinical. They are not a super warm tube.
Pricing above includes matching in any quantity you need at no extra charge.
All power tubes are Platinum Screened & Tested to the highest standards, including a 72-hour burn in process, and testing at real-world voltages.
Every power tube is different. This applies especially to power tubes like EL34, 6550, KT88’s, etc. Two tubes can be brand new in the original box, with one testing at [as an example] 6500 micro ohms, the next one at 8600 micro ohms. Both tubes would be considered "new" by the factory, and not defective. While the weaker tube isn’t "defective," it will certainly have a shorter life. So if you pay 10% less, you might get a tube with a significantly shorter life. The big lie from manufacturers of tube equipment and tube dealers themselves is that they “reject” these tubes. It’s not true. You can imagine the nightmare that would create for the tube factory if people are sending back 50% - 80% of the tubes that get shipped, coming back in all kinds of condition.
As the owner of Upscale Audio, a company that has supplied tubes into over 50,000 components, and someone obsessed with treating your amp like it’s my amp, I can tell you in no uncertain terms the factory doesn’t take them back. The only tubes they will take back are tubes that have shorts, gas, or measure BELOW the minimum number they assign for that tube type (it varies from type to type, so don’t bother trying to figure that out).
I’ve overcome that issue for you. I can say with calm assurance that we pay the factories more for our tubes than any other tube seller, and we ensure that we receive the absolute cream of the crop. This flies against the logic of how to run a business: The way you make money is to pay less for the goods you sell! That’s what most ANY business owner will tell you. We also don’t sell certain brands of tubes because while they might be cheap and sometimes good, they can be more trouble than they're worth. We pass on a lot of money as a result.
Upscale Audio is the only dealer that does what we do on a grand scale, and have a deep understanding of high end tube electronics. We’re the only dealer that manufacturers give a thumbs-up to, and recommend to their customers. And I promise you only the best.
- Kevin Deal