Do SE transfomers get hot?

[RockysDad]

I was thinking of getting those cheap and ugly SE trannys from Edcor and wanted to stick them in the chassis and out of sight. My question is would these get hot in there if I run them with about max output of 5W or so? They will most likely be not be driven that hard under normal listening conditions but are they going to generated any heat to damage them? Just wondering...

[alexmoose]

Hello!

I have two Hammond 125CSE's mounted on the underside of my 17" by 10" by 3" steel hammond chassis. and they don't get hot. I am running them with an El34 SET amp, and they have no problem at all.

I wouldn't worry about it

-Moose

[ak_47_boy]

It does not matter if they get hot at full power. When they get hot at low power that is bad, leakage.

[tubelab.com]

I have received many questions about output transformers that get warm or even hot. The amount of power dissipated in an output transformer can not possibly make it get hot. In some cases maybe slightly warm, but not hot. Now we have all found amplifiers where the output transformers get HOT, too hot to touch. Why? In every case that I have seen it is caused by radiant heat from nearby output tubes. Especially with flat black painted end bells. So in your case the transformers may actually run cooler under the chassis.

In the case of your Edcors (I am using the XSE15-8-5K's) they are fairly efficient transformers. Lets say you really crank things up and run 10 watts into them (yes, I have tried it). About 9.7 of those watts come out of the transformer, and go to the speaker. 300 milliwatts are lost in the transformer. Now to get 10 watts into the transformer, you are going to need a big tube (Electro Harmonix KT88) and you are going to run it hot, lets say 100 mA (the Edcor works best at 60 to 80 mA, but this is a worst case example). My transformer measures 130 ohms of DC resistance. This will drop 13 volts at 100 mA. That puts 1.3 watts of DC dissipation across the transformer, plus the 0.3 watts of AC loss.

For a class A amplifier the average DC current doesn't change, so the transformer dissipates 1.3 watts at idle and 1.6 watts at full power. This is an extreme case, your less extreme case will probably see under 1 watt. A transformer of this size will have no problem dissipating 1 watt if a 1/2 inch long resistor can do it.

I have used the same pair of transformers for several test cases, including the KT88 amp which can put out 14 watts in UL mode, they don't even get warm. The amp now has Transcendar transformers in it which are much larger. They get warm. Why? KT88's mounted 1 inch away operated just short of meltdown. The black transformer cases absorb much of this heat.

Some SE OPT's have DC resistances over 300 ohms. These may become slightly warm in normal use. A power trasnformer may see 200 watts of continuous input with 10 watts or more of loss. They get warm, and some (Hammonds) get HOT. This is normal.

[RockysDad]

Cool, also this is good news for the trannies. Anyway, I was thinking about building Tubelabs Simple SE amp using the KT88 in triode mode and since the man himself says its okay then I'm not going to worry about it. This way the top of the chassie will look alot cleaner. Thanks for all the responses....