[Elecraft] K3 Main and sub S meter readings different.

[Martin Sole]

This is hardly a significant matter but it's been bugging me. Just gotta 
know!

My K3 is an early radio S/N 298. works great receiver has 13k, 2.8k, 
1.8k and 400Hz filters . About a year ago I added a KRX3A sub receiver 
which has just the 2.7k filter. It works fine but the S meter shows 
significantly different to the main receiver.

I have done the receiver gain calibration using the K3 utility for both 
main and sub receivers and set the main receiver S meter as per the 
manual in the CONFIG menu. No settings for the sub receiver S meter???

As per the manual after adjusting, pre-amp on, S mtr nor, 50uV = S9 on 
the main receiver but sub receiver with the pre-amp on shows S9+20dB.

Varying the bandwidths and signal levels makes little difference and the 
variation between main and sub receiver S meter readings remains quite 
large.

How can I correct this to achieve similar values on both receivers?

Friends K3 with sub both of similar vintage and both with same filters 
doesn't show any variation.

Is this just down to roofing filters?

Martin, HS0ZED