I have restored several of these. The first one was in a right mess but I was amazed at the performance of these receivers. So it was sandpaper, paint, parts and modifications.
Transformed to this...
The front panel was in a terrible state so completely stripped that, sprayed firstly with an etch primer for aluminium and some layers of flat black paint+primer and relabelled using Letraset. Finally a clear coat to preserve
the lettering. I have found the Rust-oleum Painters Touch+ spray can paint to be easy to use, doesn't clog or splatter and covers well. It is also reasonably well priced. Recoat within 30 minutes or after 48 hours - I
got caught on the chassis - even after 48 hours in cold weather the first coat lifted when resprayed so make sure the first coat is thoroughly dry before applying a second. The Letraset I have is a very old set for electronic
equipment - maybe others have some ideas on how to relabel a panel some other way.
With health and safety the way it is I am very nervous about the safety of the mains wiring on these receivers. This receiver didn't even have a mains earth connection. The internal mains wiring seems to me to also leave a lot to be desired so I have removed the mains supply from the receivers I have worked on. There is a socket for a 12v supply on the rear panel so a 12v power adapter can be easily used. Older style adapters that use a transformer may be good but I found a number of adapters gave a lot of noise in the receiver. I found a 12v 1A adapter that is used on Huawei modems very quiet and worked well for this receiver. A good external aerial and earth is needed for these receivers. Lots of capacitors needed to be changed, sockets and corroded parts replaced.
A common modification for these receivers is to change the lock light to show green on locked and red when unlocked which is much more intuitive than the original design. The modification of the lock light described here comes from other places on the net but the layout described here may be of use. Use a tri-colour LED which has a frosted lens. The clear lenses are way too bright and distracting.
A DDS unit was fitted to a Tait T198 and the details may be downloaded here
Download circuit and code as zip folder
Do note that the solution is not perfect. The Arduino does have some spurious signals - 147600 and 146400 are particularly impacted on receive. Not likely to be much bother for most and it is still a heap better to be able to select operation anywhere on the band.