LF: Tuning inductance for 137kHz receive.

["Martin Evans" <books@mollies.freeserve.co.uk>]

I use a decade inductance bridge to series tune my  (approximately) 50m 
end-fed  inverted U wire for 137kHz.
It uses 3mH - 2mH is too little, 4mH is too much. Obviously I need to be 
able to vary this inductance rather more finely and I thought of using a 
small variac (don't laugh!) as a variable inductance, connecting one end, 
and the tap, in series with the wire.
Anyone know what the "inductance per turn", or total inductance, of such an 
animal might be?
Any idea if it would work?

Yes, I know I should wind a coil & tap it, but I like to be different!

Martin  GW3UCJ  Swansea, South Wales.