Tube amp question

FWIW I rolled from stock EL34s to KT150s on my PrimaLuna Dialogue Premium HP integrated and it revolutionized the SQ from that integrated. Very happy with the decision to roll to the KT150s. 

Hello Falconquest. Tubes work by making electrons flow from the cathode to the "Plate" (or anode). "Plate voltage" refers to the amount of attraction (positive voltage) we apply to the plate to get the electrons to flow. The higher the voltage, the more eager the electrons are to flow. We control the amount of "normal" flow by establishing the "bias" (the no Music) flow by appropriate circuitry. By applying a signal (the music) to a fine screen (like the one that keeps the flies from coming in your window - the grid)) in between the cathode (a cylinder of metal coated with a substance the produces a cloud of electrons when heated) and the plate. Physical construction of the tube's innards vary, but you get the idea. The normal current flow is changed by the signal on the grid. It's that change that interests us. That changing electron flow goes through a transformer. The transformer has two sets of wires wrapped around it's metallic core. The Primary Winding carries the current going through the tube on its way to the source of positive voltage. The current varies with the music and produces a voltage in the Seconday Winding of the transformer. The transformer's secondary is connected to your speakers and produces the sound in your room. There are ways of eliminating the output transformer, but it's quite a trick. The easiest (and cheapest) way to get more power out of the amp is to raise the Plate Voltage. But that shortens the life of the tube. So, since it's the change in the current flow through the tube that produces the musical output, if we can get the same amount of current change at a lower plate voltage, we get less wasted heat, lower power consumption, less expensive output transformers, and longer tube life. Bob Carver produces certain models of amps with tubes that run so cool that you can put your hand on the tubes while the music plays and not burn your hand. Those tubes last for decades, not years. Happy listening.

@boomerbillone  Thank you for the insightful explanation!

While I agree with you that a tester that cannot properly test a KT150- shows the limits of the tester, ( BTW, yours- nor any Hickok- I am aware of can test these tubes--and your KT88 spec is no good for them) it also points to the fact that they need more voltage than 400 volts to come to spec, IMHO.

I don't think the Hickok subjects tubes to full operating voltages. There is no B+ voltage adjustment for that purpose. It seems that you have to explain why 400V is specified as an operating point for that tube when in class A mode.

I just wanted to close the loop here. I received the KT150’s yesterday and carefully installed them, I turned the amp on and allowed them to warm up and adjusted the bias (which took minimal adjustment) then let it settle in for several minutes, started some music and s-l-o-w-l-y raised the volume. They worked just fine. Not only did they work fine but they sounded great right out of the box. I could tell the music had more authority over the entire audible spectrum. I was very taken by how clean they sounded and the level of detail.

I had some work to finish up so I sat typing on the computer listening to Tubular Bells that randomly came up. Near the end of the piece Oldfield introduces the different instruments. The first time he spoke I nearly jumped out of my skin because his voice sounded so real. There was someone in the room with me! I only have about an hour or so on the tubes but already they are sounding fantastic! I don’t know if I am indeed getting everything out of them, I’ll let that debate rage but I sure do enjoy what I’m hearing!