Drake Mods - SPR-4 Receiver
Authored by VE3EFJ
10.0 SPR-4
This all solid state receiver is a essentially a solid state general coverage R4B. It is extremely sensitive and stable. The frequency is 'programmed' by installing the appropriate crystal - one of up to 23 into the sockets behind the band selector switch. Options for the SPR4 included a noise blanker and various adaptor boards to allow it to transceive with the T4XB. The noise blanker is nearly impossible to find on the used market and it is best to get one with the receiver.
There are few weaknesses or vices in this receiver. The AGC design is weird and in certain points, very high impedance. An 11 meg ohm input meter will drag the AGC down.
The SPR-4 uses the same PTO and dial plates as the R4C. Some models were specially constructed for the FCC when they cared about the mess on CB and had the CB channels marked on the dial plates in red. It is done in an ingenious way and is fascinating to watch in action.
There was an 'early' model SPR-4 and a 'late' model. The exact differences are sketchy at time of writing. One definite difference is in the audio board around the area of the power output transistors. Late model SPR-4 used a pair of EP-487 TO220 transistors. Early model SPR-4 used transistors with unique mounting, similar to the X style UHF transistors such as an MRF901. The audio boards are interchangeable and new ones still available in 1996. If you have an early SPR-4 with audio troubles, replace the board, for the unique audio output transistors on the 'old' are NLA.
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