Power tube operating temperature a good proxy for power output???
OP, I would wonder on that one, myself. I’ve used thermal guns, sense they became available to mechanics. Take your readings at several different spots. The top may get the hottest, but that’s not the actual plates, wires or glass. I suggest you put 6 dots on the valves, with a marker. I would aligned the marker dots with the pins. Upper, mid and lower on the valve in two marked spots per, Upper/Mid/Lower. I suggest a GOOD warm up AND playing at a given volume. I’d do a Low, Mid and High volume, test, too. When you collect your data, average, and see if thing look more in line. I suspect "Idling", is one set of numbers. Different loads, will change the temps, and the numbers will start looking closer.. Remember YOUR hand position too. If it's deck height and 6 " away. do the same for all. It's the most important part if you really want to know. "The reference" points, have to be the SAME. The expensive valves you have, for the sake of keeping them looking good. Be careful removing your marks (if you do) Isopropyl can take off the silkscreen, or information on the glass valve, GEs, RCAs, Tellies, Volvos, Mazdas, (you know the powder wipes right off.) Happy holiday, happy listening Regards |
The output tubes are designed to run hot. In a typical operation, I measured the turkish proxy output of the 7591 and EL84 types running north of 300 degrees Fahrenheit on a glass jacket, even if it seems a bit daunting compared to the world of solid-state components. In AB1 two-cycle mode, even under no-load conditions (no signal), at 34 mA cathode current, your 7591 tube plates dissipate about 13 watts per piece, and some standard Fisher devices have heated lamps much more than that. That's like having a 60-watt bulb under the hood, not even considering the heat from the shields and other tubes and components such as power resistors. |
