In many ways it is similar to the quandary the the developers of Enterprise faced. they couldn't have gear that looked more advanced than the original series and yet cellular phones were quite common and making the previously cool communicators with the flip grill look dated already.
With dieselpunk you need to make something that looks vaguely 1940's vintage but also has futuristic elements to it. I worked up some principles to follow, at least for my stuff.
1) It's clunkier than 'mainstream' SF gear. A communicator that can reach orbit will be the size of an old style phone receiver. But it will have some cool striping to let you know its futuristic and be capable of video calls.
2) Angles. Lots of angles. Streamlined gear is too modern looking. You want a comm that you could beat someone to death with? You came to the right place.
3) Gear is usually single purpose or has a few related purposes. The comm-corder for example is to make and store video and logs. It also has a night vision setting and that's abut it. If you want to transfer recordings to your computer you either remove the internal drive or hook up a cable. Wifi is not dieselpunk. It's a Martian conspiracy!
4) Some of the gear is fragile. Yes you can still kill a person with it but you might break a lens. The comm-corder has a shield that flips over the lens when not in use or keeps buttons from being broken if you drop it when the friendly fauna you're recording goes demogorgon on you.
5) Equipment requires additional time and perhaps some skill to operate. Take the very rare multi-scanner (TM). The toggles on the left are verbs such as measure, map, track, compare. The toggles on the right are quantities the device could measure: ionizing radiation, EM, gravity waves etc. There are switches for modifiers, conditions etc there as well. While in actual play the device could perform most of the functions of a tricorder (real TM) it would require some programming knowledge and perhaps a round or two, not the instantaneous scans of say that ghost detector app for you smartphone.
As a final note most of this stuff is not pocket sized. They can be outfitted with straps or carried in cases when not in use. Small packs may be necessary.