ACME 30 K.C. IF Transformers

     The ACME 30 KC IF transformer was first offered in May 1924. This transformer is most often found in the Experimenters Information Services (Leutz) Model C superhets. As a matter of fact, the first Leutz superhet that I ever purchased (in 1985) used this type of transformer for the IF amplifier. I sold the set years ago, but have since acquired four of the ACME 30 KC IF transformers. The ACME IF transformer has a fairly large iron core, and, like a number of other early transformers, it peaks at the very low frequency of 30 KC.
     There appears to be at least two different varieties of this transformer. The first variety has a small coil assembly and the second variety has a large coil assembly. I have three each of the first variety and one each of the second variety. The two different varieties are easily distinguished in the photo below.

     ACME 30 K.C. IF transformers. Variety 1 (NOS) on the left and Variety 2 (used) on the right.

     The table below details the electrical characteristics that I have measured on each transformer. The measurements include the peak frequency, the upper and lower 3 dB roll off points, the frequency bandwidth, the relative gain per stage at the peak frequency, and the DC resistance of the primary and secondary coils. The DC resistance is the easiest thing to measure and it will give a quick check of the functionality of the transformer. However, the only way that you can tell how good a transformer will work in a set in harmony with the other transformers is to chart their individual frequency peaks, bandwidths, and gains. A transformer that meets the DC resistance check alone could still be a long ways off the peak frequency of the other transformers and this could destroy the operation of the set. The methods of measurement and other pertinent information is found in my IF Transformer Database, linked from the home page or here.

     The two NOS transformers were probably manufactured in the same lot. The other two transformers were manufactured in different lots. The particular manufacturing lot does make a difference on peak frequencies. As can be seen in the table, the peak frequency of the second variety (V2) transformer is quite a bit different than the other transformers. It would still work in the circuit because its bandwidth is so wide, but a different transformer would work better in the circuit. Note the lower 3 dB frequency cutoff point. Most of these transformers are down to about 20 KC at the lower point. However, at 10 KC the transformers still exhibit a gain of about 5 (these results are with a secondary coil reference of A-, and the bandwidth gets much wider with more positive bias - see the IF Transformer Database). The very low frequency response is one of the main problems with the 30 KC IF transformers; the transformers amplify audio frequencies! This characteristic makes a relatively noisy receiver.

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