How hot KT88 get? Anybody take a reading?

[jhl1963]

Hi guys, has anybody taken an IR reading how how hot these tubes actually get at the glass, 1" above/ 3" above etc or any reading for reference for that matter? We talking 120/150/200 degrees f?

Thanks a bunch!

[speakerfritz]

in actual use it will vary...most kt-88's have a max allowable spot temp of 250 C.

[Bob01605]

Below are the temperature readings (in Fahrenheit) at various points on a VTA ST-120 tube amp that had been on for 5 1/2 hours playing music at normal volume levels. The ambient temperature was 69 degrees F. The tubes used were the Tung-Sol KT120 output tubes rather than KT88's. KT88's would (IMHO) give slightly lower readings. Plate temperatures of the KT120's were over 300 degrees F on the REAR tubes but under 300 degrees on the FRONT tubes which have better access to circulating air. I neglected to take a reading on the Weber WZ68 solid state rectifier used in the test but it was plenty hot also. Note that the left side of the amp is warmer than the right side. This is normal for an ST-70 type amp because the rectifier (tube or solid state) is on the left and passes plenty of current. This adds extra heat to the left side of the amp.

Bob Latino

[jhl1963]

Thanks Bob, this is helpful.