How much cable is between the radio and external tuner? The SWR will be different at each point on the feed line. For the higher bands the difference can be big if the cable length is long compared to the wavelength. Have you checked the SWR with a 50 ohm dummy load? Maybe the SWR bridge in the external tuner needs calibration?
Hope this helps.
Bill: There is a 6' jumper from the 6300 to the SB-200 and another 4' jumper between the SB-200 and the MFJ tuner. I have not tied onto a dummy load (on 'extended' loan well prior to my acquisition of the 6300)
Thank you both for your replies. I look forward to additional input.
The internal tuner on my 6500 tunes my loop quicker than my external auto tuner in some cases, but never tunes it as low as the external tuner.
Attach the antenna to the 6300 and click on ATU to get a low SWR.
Then disconnect the antenna and add the 10 feet of cable onto the feed line.
Reconnect the antenna, now with 10 feet of additional cable and with out clicking on the ATU see if the SWR is the same.
you can't use the internal tuner to tune the amplifier because once you attach an aerial and a 2nd tuner(962) it is going to try and match the combined impedance of the amplifier 2nd tuner and antenna, I am not familiar with the sb-200 but the bandswitch may have some bearing on the impedance at the amplifier input,.
Hope you get it sorted. Just don't try to run with both tuners in circuit at the same time.
If you don't have a dummy load you could be running round in circles for ages..beg borrow or steal one..Hi!