PHILCO PHORUM

The Correct IF Frequencies for Model 90

When it comes time to perform an alignment on a Model 90 receiver, there has been a great deal of confusion over the years concerning the proper intermediate frequency to be used.

Model 90 receivers were made with three different chassis. The first used two Type 45 tubes in push-pull output. The second used a single Type 47 output tube. The third used two Type 47 tubes in push-pull output.

Comparing the circuitry of the first and second versions of Model 90, one quickly notices the similarity between the two. The front end of both receivers are virtually identical, as is the IF circuitry, save for the added automatic volume control (AVC) in the second version and the lack of a "normal-maximum" switch in the second version.

A serious error has been perpetuated throughout the decades in some printed service data regarding the proper intermediate frequency for the second version of Model 90. Now, the error has been corrected once and for all.

It is known that the first version uses an intermediate frequency (IF) of 175 kc. The third version, using much different circuitry, has an IF of 260 kc. The error I referred to earlier was that the second version of Model 90 used an IF of 260 kc. This is INCORRECT. Attempting to align a second version Model 90 chassis with an IF of 260 kc will result in extremely poor performance, or even a "no reception" condition.

REMEMBER: The proper IF for the second version of Model 90 (using a single Type 47 output tube) is 175 kc.

The table below should simplify things for you: