[Boatanchors] OPTxfr loading

[brianclarke01 at optusnet.com.au]

Hi folks,

I should rephrase. I have used 'high' and 'low' load in possibly a confusing way.
So, I have rewritten my earlier response in what I hope is clearer prose:

When a valve amplifier is operating at full volume, the Voltage swing at 
the plates of the output tubes should range from 0 V to twice the supply 
Voltage - when the secondary is loaded. When there is no secondary load, 
the load reflected to the plate[s] is negiligible and the upper excursion will be 
even higher than twice the supply Voltage. The only load is the magnetising 
current [usually less than 1% of normal load current and mostly reactive] and 
the reactance of the primary. Plate Voltage excursions are now likely to 
result in flashover and permanent carbonisation inside the transformer.

When the secondary is shorted, the load reflected to the plate[s] is a very low 
resistance. The Voltage excursion will be much lower and no damage can 
occur - it is almost impossible to draw enough current to fuse the primary 
winding.

73 de Brian, VK2GCE.