Just a note that the units can be modified for 6v heaters, but this requires changing the transformer and low voltage regulator. The HT volts can also be adjusted. These are well-built, professional-standard units. Further deatils from https://www.eskimo.com/~novatech/grandad … onics.html. Cost of my unis was only $50 each, but I understand that a new batch would cost more ($60 to $80 per unit). Compared with some others on the market they are very good value considering the build quality.