This circuit is very similar to all small amps, (no tone control, 5Watts output and 8"speaker of the 40s, 50s and 60's, such as the National 'Studio 10' (1965) and 'Westwood 1201E (1959)'.
This circuit diagram is pasted inside the amp case, and is only a few inches square. I can not 'blow' it up any more from the picture I have, and I can't 'scan' it. Sorry!
We desparately need to find and display more schematics for any early National and Dobro amps, also for the whole range of Valco made amps. Please send in any you have, or find. Thanks!
NB. I often get emails from folk starting "I have a Valco/Supro/National/Dobro amp model 51"..... Although the plate on the back of post-war amps usually said something like 'Valco, Chicago, 51' The Chicago 51 actually refers to the postal address of the company and is not a model number.