Valve (Toob) o/p Transformer vs speaker Impedence thread

[Swedish Chef]

Sorry to be a bind!
I read a post the other day about the effect (on the o/p stage of a valve power amp) of changing the impedence of the speaker without the turns ratio of the tx. I think PRR wrote it. I am trying to work through how it would effect the o/p tx in particular if, for example, you ran an 8ohm speaker on the 4 or 16ohm taps. I guess if you ran the 8 on the 16ohm tap the o/p stage would be under-loaded (is that a word?) but would the tx suffer? Obviously it is dependant on the spec of the tx...
Anyhow could someone point me to the thread as I don't seem to be able to find it with the 'search' function.
Cheers

chef

 

[PRR]

> would the tx suffer?

So what if it does? There is no ASPCT (ASsociation for Prevention of Cruelty to Transformers).

A too-low load on a power transformer will, of course, make it run hot. Heat is a function of the power lost in the transformer and its surface area. The overall size of large power transformers may be dictated by heat issues. But the size of most audio transformers, at least up to 100+ Watts, is not set by temperature rise. They usually have to be big for low loss and good bass with low distortion. Push-pull audio transformers run stone-cold (if you avoid the heat from nearby tubes or other hot stuff). SE transformers may run warm, but rarely hot, and the extra heat from audio abuse is always a small fraction of the idle heat. And speech/music audio thermal levels are a small fraction of an amplifier's maximum level: you might be able to cook a high-powered amp's transformer with sine-wave test tones, but not with anything you would listen to.

http://www.groupdiy.com/index.php?topic=129023

 

[Swedish Chef]

Thanks PRR!
I thought not, but when you buy these big lumps of iron from across the pond, it pays to measure twice, cut once.
I wanted to check with teacher that my cut line was square and in the right place.
thanks for being so square... :shock:

You know what I mean... :green:

chef