[Amps] Alpha vs Henry

[Roger (sub1)]

On 4/6/2011 4:07 AM, Patrick Barthelow wrote:
> Gentlemen:
> If you are pushing for enhanced reliability in a Ham manufactured amp, 
> run above its ratings,
> say a Heathkit SB 220, and focus on the  heat in the transformer being 
> a power limiting,
> or a long term reliability factor, and since I would guess the the 
> source of the heat, and probably
> the location of the highest  temps is deep in the center of the core 
> laminations,
> could you significantly lower the transformer temp where it counts 
> with external cooling
> fans on the transformer?

Probably not. I think Carl has addressed this specific issue in the not 
too distant past.

> If the external core of the transformer under heavy Amp use, were
> very hot to the touch, sort of "ouch, that's hot!"  with Pain 
> threshold in 1/4 second of fingertip contact,
> how hot might that be,

That's about 50 C or 122F for most folks.

> and say, if it was say, 190 F on the outside of the laminations,

I'm not sure the older transformers would be happy with that much heat 
and I think that might be a tad high even for the new materials.  Again 
I'd have to bow to Carl's knowledge of this subject. I do know the new 
materials available will go much higher than the old materials.  Then 
you have to take into account the effect on other components.  How well 
do the filter caps, meters, and other *stuff* stand up to 190F?  The 
inside of that amp is going to get pretty toasty with the PS running 190.

> how much hotter is it likely to be on the inside center core?

Substantially, but you are going to have to talk to a transformer guy to 
get some specifics.
Transformers are much better at heat retention than radiating it.

I can put my hand on the core of the transformer in my amp after a 
couple hours of ragchewing and it's only luke warm.  OTOH that 
transformer weighs about 60# and is IIRC about 3.5 or 4 KVA.

73 and good luck

Roger (K8RI)