Testing Marshall DSL401 OT

[rf7]

I've got a DSL401 that's putting out about 1W total. I've tried new tubes already. The signal looks OK out of the PI, so I tried the geofex OT test. I fed the heater supply voltage of 6.3Vac into the 8 ohm tap of the secondary. It was pulling 45ma, but I was only getting 41Vac out of the primaries. Actually one half of the primary measured 38Vac, the other measured 41Vac. I've never done this before, so I was wondering if those were reasonable results? I thought the primaries should actually have a higher voltage on them.