Pre-amplifiers for vintage Grass polygraph. 7DAC uses (2) 12AU6 tubes (not present). 

All knobs missing, parts not missing. Polygraph units totally untested. Lot: 9. Comes with 12VAC cable.

See my other Grass equipment lots. Combined shipping available: fill cart with all items you want from my store, click "purchase," then click "request total from buyer." A revised invoice will be sent to you that reflects the lower price.