Transmitter Type T1154M, a restoration. /cont

Unlike the R1155, the T1154 requires a minimum in terms of component replacement. Similarly, there should be no requirement to replace any of the wiring either. This is very fortunate given the transmitter’s construction which makes getting access to some of the central locations extremely difficult. There are only three capacitors which require instant replacing. One of these, pictured right is situated in the bottom left rear corner of the chassis.This is a compound block capacitor comprising C21 (0.5uF) and C8 (0.25uF). These values are actually stamped into the top of the capacitor. Curiously, this does NOT tie in with the manual, which states that both capacitors should be 0.5uF and gives the Stores Ref. No. As 10C/2053. However, T1154 variants A, B, D, E and J did have C8 as 0.25uF with the identical Stores Ref. No. A second T1154M, this time with Oct. 44 printed on the side of the block also has 0.25 and 0.5 stamped into the top of the can. Unfortunately in this case, the 0.25uF section is ‘leaky’ and the 0.5uF section is a dead short! I probably have to conclude that the documentation is out of date and trust the capacitor with the 1944 date code on it. Fortunately, these block capacitors are of aluminium construction and it is therefore very easy to drill a series of holes, making it possible to remove an unseen section of the can. I then drill into the foil capacitor at various points.

C21 and C8 (re-stuffed)

This is extremely messy and results in mountains of foil and paper. I then gouge out the innards with a wood chisel. Sometimes, the bulk of the capacitor will come away all at once. The walls of the can will likely be lined with sheets of Paxolin. These can also be removed. When the can is more or less empty, it is a good idea to apply some heat from a heat gun and allow any residual wax to melt and run away. In line with the markings stamped into the can, in this case, one section of rolled foil was indeed twice the size of the other which would tend to confirm the values as 0.25uF and 0.5uF. It is then simply a case of soldering the new capacitors into the solder spills before screwing the block back into place. The other capacitor which will require attention is not so easy to access. This

is C26 (2uF), part of the bias circuit associated with the Carbon Microphone option. It is mounted on a sub-chassis along with LFC3 and R27/R28 (a compound wire-wound resistor) on the wall separating the PA compartment from the Modulator and VFO, above V1 and V4. Again there is a discrepancy in the documentation, which in Fig 11, shows LFC3 as being at the back, under S5 (Master Switch). This is actually T1, the input transformer on the modulator. To get this assembly out, it is necessary to remove all four valves. Then using a long screwdriver, remove the two screws retaining the rear top-cap assembly. This is necessary to gain access to the one counter-sunk screw. I also found it necessary to make my own very short screwdriver to remove the sub-chassis since there is no access in through the right side. Once all four screws are removed, the assembly can be carefully pulled forward. Note the corner which has been broken off LFC3. I don’t understand how I missed this at the time, but I was stumped as to why the modulator was not producing AM when the Master Switch was set to R/T. The clue was that there was no bias on the microphone. This particular T1154 had not been well treated. The socket for V4 had been smashed and it is likely that LFC3 had been damaged at the same time. Probably the reason I didn’t pick up on

this fault earlier is the fact that the tag forming the junction between R27 and R28 was missing, as was the wire between that point and LFC3! Maybe if there had been a lose wire I would have spotted it? Fortunately the broken end of LFC3 was accessible and I was able to solder a wire onto it and link it to what was left of the damaged tag on R27/R28, thus restoring bias to the microphone.

Carbon Mic Bias Assembly