The Model 38, Code 123 employs a type 1A6 detector/oscillator tube. A change was made recently in the circuit of this model to reduce the amount of background noise [or hiss]. The connection from the antenna series condenser to the top of the volume control was removed from this point on the volume control and connected directly to the variable arm of the control. This change in circuit affords better regulation of the input signal strength and also of the sensitivity of the receiver.
In the late factory production the volume control has been changed from Part No. 33-5087 to Part No. 33-5094. The by-pass condenser, Part No. 628K, (.15 mfd.) is connected from the lower end of the new volume control to ground. The overall resistance of the new volume control is exactly the same as the earlier control, but the rate of taper at the low end is greater in order to afford better control of volume on powerful local stations. The addition of the condenser further adds to this control on the strong stations.
From the Philco Serviceman – February, 1935.