I assume you mean Regency HR-2B. Don't think there was a model HR-28...
If you have a model HR-2B, It was about 10 watts output and required a 4 pin Cinch Jones plug
which connects in the rear and operates the rig on 12 volts DC. Any well regulated power supply
providing 12 VDC at about 10 Amps would work
This rig uses crystals to set the frequencies. One for the receiver, and one for the transmitter.. If
you fill the rig up for a maximum of eight channels, it will require 16 crystals. Not sure what
crystal manufactures still make a crystal that will work for you. Once you determine what frequencies
you need for your area, you might run a wanted add. There were many of these rigs sold a someone
should have some crystals laying around they would be willing to sell..
Another problem, This rig was before wide spread use of tones, and has no encoder, decoder, so
it would require some kind of external tone unit so you can access repeaters that require a tone.
You might want to consider this if you need to buy everything ?
Power supply $ 50
16 Crystals $ 90
Power cord $ 10
Manual (Used) $ 5
Tone encoder/decoder $ 25
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$180
As you can see, it's not a very good investment to get started unless you use the project
to learn how to construct and get things to work. $ 200 will get you a new synthesized rig
that would permit you to avoid all the items above except the power supply, if you would
choose a mobile (12 volt) radio... Good luck