pentron: NL-4; Emperor II
The following is a scan of my personal copy of page 48 from the 1959 Radio Shack Catalog. This page shows a range of Pentron tape recorders, and was apparently the last year that Radio Shack sold Pentron. The 1960 Radio Shack catalog has no Pentron products.
Check www.radioshackcatalogs.com. This is one of best archival web sites on the web.
I inherited the NL-4 at the bottom of the page, and I have done some restoration to it. However, this unit was badly compromised when it was incompetently converted from 117VAC/60Hz operation to 220VAC/50Hz operation. The 6.3V filaments on the second channel amplifier run around 7V, and the main pulled on the motor was turned very poorly and has a severe wobble. I bought an Aristocrat NL-2, which I will use for parts. A long term project. My father bought it slightly used shortly after I was born in 1959.
I don't have a schematic diagram, so I will use the Sams schematic for the NL-3 as a guide. Sams did not make a schematic for this very low volume model.