The Raytheon Series 4 and Series 5 models were unique in all the Lectron System models ever produced by any Lectron System seller or reseller. Featuring a beautiful hard wood case and the deluxe base plate, these two models were of the highest quality Lectron System products ever made. The Series 4 offered 50 experiments and was priced at $130.00. 

The Series 4 and 5 also shared the same expanded ‘Lectron Laboratory Manual’ showcasing 57 experiments.  The manual is available for downloading on the Raytheon document page.

It is interesting to note that the version 2 of the Series 3A offered 64 experiments and was priced at $50.00, $80.00 less than the Series 4 and offering 14 more experiments.

I have never seen a Series 4 on eBay  since I began the Lectron.Info website in 2012 so this is likely a very rare model to find/acquire.