R-145 Redifon

The Redifon R-145 Receiver was produced by Redifon (U.K.) in 1959 for use by various government departments. It is a massive and monumental piece of engineering excellence. Once you manage to lift it onto the bench you will see that the chassis is cast, very similar to the Murphy B40 series of radio receivers in construction.

The set was designed for high stability operation, with the oscillator having a stability of 250 cycles and the BFO 20 cycles. The set covers 2 - 30 Mc/s in fourteen switched bands of 2 Mc/s each using a Turret tuning mechanism. It is a single conversion Superhet on 2 - 4 Mc/s and double conversion on higher bands. The optional sideband adaptor is fitted to this receiver and adds an extra stage of conversion. This set was dead on that section and there was a quick fix that resolved this by replacing a dead tube and one resistor.

This set is a complex receiver, and very heavy at 36.2 kgs (80lb). Needless to say when you place it on your bench you need to make sure it can handle the weight. I was amazed at how well the set performed for a set of this vintage and it being of this type of construction, it has all of the items and options that you would expect a top end communication receiver to have. The set has a AF filter, and IF selectable bandwidth, BFO with a reduction, tuning with reduction dial, Noise limiter, Crystal marker, and upper and lower Sideband.

I tested the sensitivity as its specification is better than 1uv unmodulated for a 14db signal/noise ratio. This set meet these criteria after an aligenemt and some selective valve repalcements in the RF and IF sections with new tubes. The set contains 24 valves and includes a mains operated power supply.

These receivers were reputedly used by O.T.C. and D.C.A. (Australia) often on RTTY links. Although it appears that these are SSB receivers, they are not by the current meaning of SSB. Rather than single sideband reception, the adaptor has the ability to select either sideband of an AM transmission, which it does to great effect. Not a set I had come across before and Thanks to Ian from the Kurrajong Radio Museum for helping me find this one.

Radio Running Video: https://www.facebook.com/tuberadioaustralia/videos/1862513400653267/

Photos:

Front of the Receiver before work to the Tuning Reduction setup. To repair and remove the reduction dial, firstly remove the fine tuning knob with a Allen key, and then the two screw on the front of the main tuning knob. Once that is removed, proceed to remove The 6 small screws holding the dial cover in place and clean carfully, Remove the two screws holding the red main pointer in place and the reduction mechacnism is now exposed. To the back of the long cylinder there is a locking ring with sloys. Unlock this by turning it Clockwise while looking at the reciever front on. This unlocks the main cylinder that holds the reduction drive, I mas a speciail too with two rods to then unscrw the cylinder as it has two holes in the front of it, you could if carfull use a cloth and pliers to hold the cylinder and unscrew it counter clockwise. Inside there are three components that are the fine tune shaft with three ball bearings, a copper clutch drag disk and a washer. Clean all of these and the bearings on the indide of the shaft that remaines in the reciever when you remove this reduction drive. Grease well and then loosening the locking ring even further return the assembly in reverse. Once you have it in place, tension the unit by screwing it in a ½ tun further after you feel resistance, this places tention on the clutch drag component, try the fine tuning and if it feels right tighten the locing ring.

Two good photos of the front and the Turret. The turret on this set was loose, three resions, 1- The Chain was slack, and there is an adjustment for that , 2- the Shaft was loose on the turret, two scres had come free, and 3- the shaft from the Band change knob to the change mechicanism had the grub screws loose. This meant that the turret was not contacting the upper and lower contacts, Yes that’s right there are two sets of contact, one hidder under the turret the other visible from the left side of the turret. I presumed that the contacts on the under side were for the bands that used the second conversion stage.

The right and left sides, showing the power transformer and the IF and Turret.