quickie headphone conversion ipedance question

[balancedtriode]

i am building a quickie to get a feel for bottlehead kits, what is the minimum impedance of headphones needed to be effectively driven by a quickie amp modified for headphone use with speco T-7010 transformers?

 

[Paul Birkeland]

250+ ohms is a good idea, although I've gotten decent results down around 100.