I want to run my Laney TF700 head as a preamp and use the effect send to a Laney GH50L effect return which then powers the output to a 4x12 cab. Does anyone know if i would need a dummy load on the TF700 to avoid frying the transformer? it only has one preamp valve and no output tubes.

Sounds silly but the amp has a headphone socket on the back which isolates the output from the speaker when used - could i use the effect send and then plug a pair of headphones in to stop load onto the tranformer?

Any help would be much appreciated!
Because I want to use the clean sound of the tf700 to colour my clean sound and then use the drive on the gh50 to boost.