- Good Morning All,
I was unable to order additional Fairchild FST3253MX devices last week and had to substitute TI SN74CB3T3253DR parts in a number of kits.
To test operation with the SN74CB3T3253DR substituted for the FST3253, I built two examples of the HF RX Ensemble II receiver this past weekend. Both receives played properly with the chip substitution although a few subtle measurement differences were noted.
I typically check supply current to the receiver board when 17m operation is selected. RX Ensemble receivers built with the FST3253 typically require 28 mA supply current on 17m. With the SN74CB3T3253DR built receivers the supply current was typically 34 mA on 17m.
Another change was the DC offset of each of the op-amp outputs did not shift away from 2.5 volts quite as much with the SN74CB3T3253DR as with the FST3253 on the higher bands.
This morning I was finally able to order a new reel of FST3253MX devices and so kits will again include the FST3253 devices.
One of the HF RX Ensemble II receivers built this last weekend is still available if anyone would like to have it. Please contact me directly.