Hot tubes!

[Markpab66]

Hello friends! I'm new to this forum, bought a World Audio Designs Kit 34 integrated tube amp just last Sunday, and it arrived Tuesday. Was ready built, seems to have been really well assembled by whoever made it, and I love the sound - I'll never go back to solid state now.
I was worried that the mains transformer seems to be getting really hot, just idling, so I took the temperature with a thermocouple, was 46°C, seemed a lot hotter than that to the touch. Would you say this seems about right? I'm totally new to tube amps, except for a Chinese tube kit I built in November.
Just for a laugh, I put the thermocouple on the output EL34's and the temp was 92°C, but the winner was the rectifier tubes - 114°C!
I can't get enough of the way this amp sounds, I hear now what all the fuss is about regarding tubes, they are great!

[bob orbell]

Hello Mark, World Audio Design had all there transformers wound with very little over current consumption, they do run almost at their limit, hence, the heat they produce, World Designs on the other hand are wound with a larger over current and run much cooler, plus the fact some mains power supply's are very high 253 volts and some lower 195 volts, the higher the voltage the hotter the transformer. I had a KAT 6550, it is still working today and still gets too hot to touch, enjoy. Bob

[Markpab66]

Thanks for the info, Bob. I'll check to see what my actual mains voltage is later on. If its really high maybe I'll invest in a Variac.

[John Caswell]

Just to add a little further,
According to one manufacturer I deal with, with modern materials, core temperatures of current transformers can reach 180ºC without damage. Also, because of keeping cost down most transformers are wound with single 230v primary, so running them on 250v will tend to make them run hotter.
Quite often I fit 1 or two NTC resistors in the primary circuit to reduce input surge (in the case of toroids) and also to lower the input voltage to the primary, therefore cooler running.

John

[Markpab66]

Thanks for the info, John. I've just checked my mains voltage - 245V. There's a date code on the transformer's, 12/02, so hopefully should be OK with all those years behind it.

[bob orbell]

That will be fine Mark, I live close to a small sub-station and of peak my voltage is 252 and my 6550 did more than 17 years and is still going with a friend. Bob