|Reslo RV ribbon velocity microphone.|
The RV was one of Reslo's earliest ribbon microphones - possibly their first production model, although I am not sure if the UR series came before or after. They share parts so it is hard to pin down which one came first.
|Inside Reslo RV mics|
The two mics shown have the same frame for the ribbon, but the magnets are very different. I believe the mic on the right to be the earliest RV design, or at least the earliest I have come across, and it uses a single cast magnet with quite a complex shape.
|Reslo RV magnets|
The mic on the left uses two simple horseshoe magnets at the top and bottom, attached to a pair of metal pole pieces, and this really sets the style for all subsequent Reslo ribbons - later models have three magnets but use a similar layout.
The UR model has a similar construction but has a rear mounted transformer. This is effectively blocking the pickup from the rear of the mic, giving it a more cardioid pickup pattern. It seems likely that 'UR' stands for Unidirectional Ribbon, although I have not seen any documentation to support this.
|Reslo UR magnets and rear-mounted transformer|
But the story doesn't end there. Many of the RVs that I have worked on have a later, smaller motor which is essentially the same as found in the RB model. Keeping common parts with the later models must have kept costs down.
|Reslo RV mics with different motors.|
Until very recently I had only ever seen 30 ohm versions of the RV and had assumed that they were all low impedance. However, the one on the left, which came in recently, has a high impedance transformer, and measures around 6.5K ohms with the original ribbon.
Reslo mics don't have serial numbers or dates on them, so it is hard to make a definitive time line for the development, and always if you have any further information we would love to hear from you.