Silver-Marshall Kit/Bakelite case IFs

Silver Marshal 210 and 211 Kit

     This is a Silver-Marshall superheterodyne kit consisting of an oscillator coupler and three IF transformers. The transformers are the Silver-Marshall 210 and 211 bakelite case design (introduced in 1925 just after the aluminum case IFs). The oscillator coupler was probably manufactured in the 1926-1927 time frame. I purchased all of these parts in the same lot so I assume that they constitute a complete S-M kit. This oscillator coupler fits the oscillator socket of my Scott superhet.
     The boxes of the 210 transformers are each marked with the peak operating frequency of 55 KC. The peak operating frequency of the 211 filter transformer is also marked as 55 KC, with the condition that it is used with the condenser or condensers that were supplied with the transformer. The number 55 is also marked on the bottom of each transformer. Did the Silver-Marshall factory measure the peak frequency of each transformer and match them at the factory? Probably not. I suspect that they may have measured the peak frequency of the 211 filter transformer only (with a capacitor they intended to ship with the transformer), then marked the 210 transformers with the same peak and shipped them as a matched set. Why do I suspect this? Because I measured the peak frequency of the non-tuned 210 transformers and got a frequency of 60 KC! The 211 filter transformer peaks at 55 KC with a .0118 mfd capacitor across the primary winding, which is the value of capacitor that they must have shipped with the transformers. However, the 211 filter transformer peaks at 60 KC with a .0100 mfd capacitor across the primary winding, and that would have made the IF amplifier a little bit more efficient.

Silver Marshal 211 Transformer
Silver Marshal 211 Transformer Bottom View

     Close up view of the SM 211 bakelite case filter transformer.

     The table below is a recording of the bandpass measurements of the bakelite cased transformers. All of the transformers were measured with the secondary winding referenced to A-.

Silver<     HOME     >St. James IF Transformers


     Silver-Marshall advertisement from the fall, 1925, Citizens Radio Call Book.

Silver Marshal ad CRCB Fall 1925


Peak Freq.

Lower 3 dB

Upper 3 dB


Relative gain

Pri. ohms

Sec. ohms

#1, SM 210

60.0 KC

36.6 KC

84.2 KC

47.6 KC




#2, SM 210

60.2 KC

35.6 KC

81.6 KC

46.0 KC




#3, SM 211 .0100 cap

60.1 KC

57.1 KC

62.7 KC

5.6 KC




     Bottom view of the transformer showing the number 55.