T1154M Ser. 86102 Restoration (/cont)

Above, inside rear of Ser. 86102 ... Below, note extra metalwork in Ser. 85660

It could be said that the photograph on the left might be described as iconic. The reason being, that the seven large vitreous enamelled high power resistors are what most people associate with the T1154 (ignoring the brightly coloured knobs!). If you do the maths, there isn’t really a lot of dissipation going on either. Some of them are only dissipating about 3W, while some are as high as 25W. The reason why they are there is because the design of the transmitter is so simple. Or rather, the PSU powering it is so simple ... 1200V and 6V. Thus, the resistors serve as voltage divider networks to provide the lower voltages for the Master Oscillator and Modulator/Side-Tone Oscillator and biasing for the PA valves.

In this case, when carrying out the resistance checks as per A.P.2548A, I found that two of these big resistors (the one on the left and the one on the right) were open-circuit. I am indebted to Michael Milne for his generosity in providing me with replacements. I have to admit to being curious as to how two of these resistors can end up open circuit whilst showing no external signs of stress. I can only surmise that an internal fault occurred. The wire from the end-connection to the resistance wire itself is NOT part of the ‘resistance element’. I also noticed that there is a slight mechanical difference between the two T1154Ms. See the photographs left and below.

I know that at the peak of Bomber Command’s campaign, (November 1943 until early 1945), fuel was often sacrificed in favour of bomb load. However the differences between the two transmitters above are so insignificant, it is more likely that speed of manufacture was more likely to be the reason for the removal of the bracket on the band-change switch and the change of shape for the relay mounting plate. Although not in the photograph, Ser. 85660 does have a capacitor across the Mag Feed meter.

T1154M Ser. 85660

T1154M Ser. 86102