Last week I put up a doublet with 36m top and 18m of 450 ohm ladder line. (13m high) It tuned up on 5 MHz to 28 MHz, but not on 3.5.

EZNEC says the impedance looking into the ladder-line on 3.8 MHz is 821+j1563 ohms. If you doubled the length of the ladder-line to 36m, the impedance looking into the ladder-line would be 53-j98 ohms, much easier to match. If you increased the length of the ladder-line to 38.5m, you would have a nearly perfect match to 50 ohms requiring no tuner at all. Of course, 38.5m (1/2WL) of ladder-line may be hard to manage on 80m but 1/2WL is much more manageable on 40m.

A 1/2WL dipole fed with 1/2WL of ladder-line is a resonant system requiring no tuner. For instance, a 65 foot dipole fed with 61.5 ft. of ladder-line would be a resonant system on 7.2 MHz, requiring no tuner.