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.

UPDATE:  2022-JUN-12

I was finally able to acquire a Series 4 model on 2022-JUN-09!  While not in great shape (the red ‘felt’ in particular is decomposing and leaving a fine mist of red on all the blocks) it was gratifying to have this very elusive model added to the Lectron Museum.

I don’t know how many units were made of this particular model.

The seller reported to me that this particular unit had been acquired by a close relative who had been a Raytheon employee back in the day.  This unit had been languishing in the attic for some 50 years or so.