During my visit at Lundahl in Sweden, we discussed some new products which would be worthwhile to add to the line up. I suggested a 1:1 interstage transformer, capable of enough voltage swing to drive a 845 output tube and for use with powerful driver tubes which draw a lot of current.
Last week I received prototypes of the new LL2753 interstage transformer. It is capable to swing 330V peak to peak at 30Hz. Like most Lundahl products the air gap can be chosen for a wide range of bias currents. My sample pair came gapped for 20mA with a primary inductance of approximately 60Hy.
Initial measurements on the bench look very promising with a nice flat frequency response and a smooth roll off without severe resonance peaks.
The LL2753 comes on a larger core than the widely used LL1660. Here both of them in comparison:
Measurements in an actual tube circuit will be done soon. Stay tuned for more results. Also a SE 845 amp with these might be coming up in the near future.