Selmer De Luxe model lap steel guitar, dating from 1939.
 
After much research and little luck, I finally found this very model while browsing the 1939 Selmer catalogue - the De Luxe, pitched as a self-contained lap steel solution including a case-loaded, fully functional valve amp. The 1939 catalogue lists this as the most expensive model available at the time, priced at £27 (about £1500 in today's money, adjusted for inflation).
 
Fully renovated by Coopersonic (Nottingham), who refurbished the amplifier meticulously sourcing correct replacement tubes, a new speaker and components where necessary. It's now a fully-playable, fully-working (albeit a little quiet, though it was built in 1939) amplifier.
 
Specs:
 
Seasoned Paralda wood body
30s Sunburst finish
Original alnico magnet Selmer lap steel pickup
Brown (faded to black) crocodile-grained rexine covered case 
1x volume and 1x tone controls
 
Condition:
 
Excellent condition for a unit nearing its 90th birthday. Lap steel bears numerous marks and signs of playing wear for a near century of play. Case is complete, with all latches and hinges functional, retaining its original lining. 
 
Modifications/repairs:
 
Amp in case fully refurbished by Coopersonic, including new period valves, serviced electronics and new speaker (original was beyond repair). 
 
Accessories:
 
None (1939 Selmer catalogue for reference only - not included!).
 
Notes and repair details from Coopersonic:
 
"So, this turned out to be quite a job. Looks like it had been stored in a shed or cellar as there was a fair amount of rust, mould etc. The controls were all corroded past redemption so have been replaced with suitable vintage parts. Similarly, the speaker had completely seized; new Jensen fitted here.
Valves were something of an issue. Obviously due to its age, it uses what are now some pretty obscure valves. Rectifier (25Z5) is OK, as are the preamp valves (6C5G). It is possible to find these types on Ebay or specialist sites. The output valves are type 18 – these were very hard to find, and some that arrived were faulty. You now have a couple of spares of dubious quality. It’s hard for me to test these properly as they pre-date my 1963 valve tester by a couple of decades.
Once I got it working there was an immense amount of hum/buzz. Whoever had worked on it before seems to have done some sensible things, and some mad/pointless things also.
Originally the valve heaters would have been wired across the mains, like a lot of old radios. This is insanely dangerous and is why someone has fitted an isolating transformer in the metal box.
It’s a fairly simple circuit – two preamp valves feeding a transformer based phase splitter into the two output valves. But the way the preamp is designed is to have max gain all the time with volume controls on the inputs. This produces an awful lot of noise unless everything is brand new and just right.
This thing probably predates the electric guitar so is not really that suitable for it. In order to make it useable I have redesigned the preamp in a more modern fashion, but using all the old components where possible (some old capacitors replaced). So, you now have a single input, and a gain and volume control, rather than two inputs each with a volume control. This allows it to get quite crunchy but not have all the noise and hum.
It’s not terribly loud, but as a practice or recording amp I think it has come out quite well. I doubt there are too many of these surviving in working order.”