Valve Art KT66 Tubes Heavy Load

Hello all,

I purchased a quad of Valve Art KT66 tubes and installed them into my VTA ST70 today. I have been running Gold Lion KT66 tubes which I like very much. I wanted to compare to the Chinese tubes. I switched off my amp after an hour of playing the stereo and I noticed that the power transformer was HOT. I biased them at .45mA. The Gold Lion tubes never loaded the transformer that much. The transformer was just warm to the touch before with the Gold Lion tubes.

I did notice that when I switched off power that the filaments took 15-20 seconds to loose all of their glow. The manufacturer must have used some heavy tungsten.

Has anyone any experience with these tubes? I am not sure if this is normal for these tubes or if I got a bum set. I do not plan to use them again and risk burning up my power transformer.

Thanks in advance.

Ed Cheek

Bob Latino wrote:The power transformer may run a little warmer but you will not harm the power transformer in the VTA ST-70 amp.

To add to what Bob said - keep in mind too that what is "hot" to you and I is not hot at all to a quality transformer. If you can hold your hand on the trafo for even a few seconds it means the temperature is at or below about 130 degrees F - that's a piece of cake for a good trafo. They can take much more. Even cheapie trafos can usually take 185 degrees F or so, and the trafo Bob's amps use is not a cheapie, it's a good quality piece.

I have a Cit II with the McShane mods and the transformers run quite hot with 6550s. If it is on for a few hours it really gets cooking, can't really hold your hand on them after a few seconds especially power trans. I am not a tech and worried a bit at first but it is OK and those transformers are huge so I guess the designers knew what they were doing.

wildiowa wrote:I have a Cit II with the McShane mods and the transformers run quite hot with 6550s. If it is on for a few hours it really gets cooking, can't really hold your hand on them after a few seconds especially power trans. I am not a tech and worried a bit at first but it is OK and those transformers are huge so I guess the designers knew what they were doing.

Much of the heat is radiated from the power tubes which are very close by, it's not all generated by the trafos themselves.

Also, as you said - you can only hold your hand on the transformer case for a few seconds. That means they are about 130 F, not even warm enough to break a sweat for them! That may be hot to you, but to a quality transformer it's cool as a cucumber!

Thanks to all of you for your helpful answers. I appreciate your time and experience. Hopefully I can return the favor someday. I will continue to use the KT-66 tubes. I wish a good weekend to all.

Why not get yourself a basic IR contactless thermometer. I find it to be a useful tool. Harbor Freight has one that goes on sale for less than $10 every now and again. Look here.

http://www.harborfreight.com/non-contact-pocket-thermometer-93983.html

dang, I paid $25 for this one, but it has a 6:1 ratio on the measuring area, VS 1:1 on the cheap one.
So from 6" I get a 1" read area, rather than a 6" circle area on cheaper one, so worth the extra $$
http://www.harborfreight.com/infrared-thermometer-93984.html
Not a problem if you're measuring a tube from 1" away.
As long as you're there, get a couple of these for measuring tube bias. I've got 4 of them now, real handy!
http://www.harborfreight.com/7-function-multimeter-98025.html