Getting the T1154 on the air after over 70 years

 Strictly speaking, I'm not sure if this example has ever transmitted since it was used during WW2?

After the refurbishment was completed I was keen to get the T1154 on the air...

Connecting up the T1154 using my home-brew power supply proved all was well. I used a 45 watt mains voltage tungsten lamp connected to the aerial socket and managed to get about two thirds brightness on 7MHz CW. The input to the PT15s was about 70mA at 700 volts (=49 watts DC input and 30 watts RF out or 66% efficiency). 800 volts should give me 90mA and 72 watts DC input, and around 48 watts RF out.

Next, I tried the other wavebands but I couldn't find a dip in the PA tuning using the 45 watt bulb. I guess the bulb impedance doesn't match the output circuit? Sometime, if it's feasible, I'll transform the output to 50 ohms and connect a wattmeter. Then I could also use my 80m dipole.

To improve the RF output I modified my power supply unit, moving the transformer tappings to 620VAC and adding an extra 1200uFx450V capacitor, making four in series to deal with the higher voltage, then changing the stabilizing zener chain to give me 7 x 33V plus a 270V zener in series. This gave me a little over 800 volts stabilized output.

Connecting up the T1154 on 7MHz with the extra HT gave me full brightness of the 45W mains lamp on CW with the PSU indicating 200mA output current. As the T1154 was designed to run with 1200 volts HT there's still scope for improving the RF output, but that will have to wait until I've built a power unit specifically for this transmitter.

Next, I'll wire up the carbon microphone and see if AM works... Firstly I'll check that the microphone is OK. Unscrewing the front cover reveals the carbon insert and pulling this out shows wiring to the switch into which is inserted a 560 ohm resistor. As this measured over 800 ohms I removed it and fitted a new one that measured precisely 560 ohms. The T1154 has a pair of sockets on the front into which you can fit standard 4mm banana plugs. I'd already bought a pair of these and fitted them to a quarter inch jack socket, red to the microphone output and black to the ground connection.
 Above RAF microphone type 10A14844, a rebadged Army microphone. Fitted inside under the carbon insert is the replacement resistor.

I tuned an HF receiver to about 8MHz and fired up the T1154 into the 45 watt lamp. Having got a nice glow in the lamp I tuned the receiver and found a good strong signal. For some reason there's a fair bit of hum so I'll have to figure out why this is. There are lots of possible reasons including earth currents, a ripple on the power supply to either the filaments of the valves or on the HT rail. Also, of course, a fault in the T1154 perhaps connected with the modulation. Pressing the microphone switch and speaking into it gave me audio. This produced some small fluctuations in HT current and lamp brightness so it looks like everything's working. Flipping back to CW turned off the modulation and produced an increase in lamp brightness which is what I'd expect.

The next step is to tidy up the wiring and discover the reason for the hum. I've ordered some new Jones sockets. Enough to connect the T1154 to an R1155 as the designers intended. Surprisingly Jones plugs and sockets are still manufactured... see next paragraph below

Usefully, if you don't have a mating connector, standard fastons fit the Jones Plug contacts. Note the incorrect mode switch knob in the picture. It looks OK but protrudes too far. Top left are the new 4mm banana plug microphone connectors which are wired to a quarter inch jack socket to match the microphone plug.

 Connecting up a T1154

I'd now like to review the purpose of the numerous connectors involved in running the T1154. Most of the power connections are carried by Jones Plugs and the remainder by miscellaneous types not generally encountered.

In the various aircraft and rescue boats in which the T1154 was used the transmitter was normally paired with the R1155 receiver and connections between the two are carried by cables terminated with 8-way Jones Plugs. Connections to the power supplies are also made by cables carrying Jones Plugs. In addition the morse key and transmit switch are connected to the T1154 via a 4-way Jones Plug.

Although there are surplus Jones plugs dating from the 1940s and 50s available, these can be very expensive. However you can buy new mating connectors because they are still made. For example Cinch manufacture suitable Jones plugs (series 2400) and these are advertised for sale in the UK and in the US (January 2016). You need 4-way and 8-way sockets and these are coded S-2404H-CCT and S-2408H-CCT respectively. Both Farnell and RS list these in their 2016 catalogues, and in the US Newark advertise them.

A new S-2408H-CCT with cover detached. Note the cable clamp screws. These are long self threading types with really sharp ends and need to be replaced with shorter normal US threaded screws otherwise, sooner than later, you'll cut yourself. 

Farnell have the 8 way which is sold, apparently together with its mating plug as 1332458 although the quoted manufacturer's code is for the socket only. Price is about £16 plus carriage from the US, a further £19 per order, also the 2404 pair (1332457)at £8.80. RS sell the S-2408H-CCT (8859134) for £8.65 but often on back order, as well as the S-2404H-CCT (8859125) which is £8.59.Newark are advertising the S-2408H-CCT coded 12M1381 at a mere $5.58. From these figures you can judge for yourself the expression "Rip-off Britain". The right angle version has the code "CCE" rather than "CCT". Eight-way plugs are coded P-2408-CCT. Astronomically priced at Farnell at £27.73 plus their US delivery charge from Newark where they're nearly $19. RS are much better at £9.85 although this is the "AB" chassis mount version. See the CCT version specs... Plug and Socket.

I ordered 4 of the 8-way and one of the 4 way from RS and after a couple of weeks these arrived so I can now dispense with the rat's nest of wires and fastons, and with the nice shiny black Jones Plug covers it'll be much safer.

Turning now to the T1154 aerials. These are connected, via an aerial switch, to a pair of single brass posts within bakelite mouldings (below). These are located on the right hand side of the chassis looked at from the front.


 Centre right the HF output, bottom right MF output and top left the "ground" connection or more accurately the connection to the airframe.

The T1154 was designed to operate with aerials found in aircraft such as the Lancaster bomber but these are not really practical propositions for the average radio amateur. In any case, to eliminate harmonics, a transmitter like the T1154 should use a 50 ohm resonant aerial and this would involve perhaps making an external Pi-network to match 50 ohm coax to the T1154 aerial connectors (at least to the HF socket). For the MF/LF band and for purists wishing to emulate original operating conditions for the HF band the choice would be a long wire but for this you'll need a method of indicating correct transmitter tuning. See below...

The aerial system in an aircraft was fairly complicated, not least because provision was made for switching between the various aerials available to the operator. Normally the best one for the particular operating frequency was selected, but as this was not always possible, due to damage for example, an alternative could be pressed into service. This explains why there are so many switches on the front panel. In order to handle aerial selection a rotary switch (below) was used which allowed the radio operator to select the best available aerial as well as using a DF system (facilities for which are included within the R1155).


T1154 Aerial Switch otherwise called the "J Switch" (I don't have one of these)

Power output was indicated via either the aerial current meter in the front panel (used only for the MF range) or an external aerial current meter (below right.. I don't have one of these) wired to the aerial selector switch. Presumably it was too awkward to switch the RF meter between the MF and HF bands?


Completing the review of connectors... those for the 1200V HT and 6V LT supplies. These are carried by a single brass post (see below) and a pair of contacts on the right hand Jones plug respectively. Both these are supplied by external power units (either rotary transformers or mains/battery PSUs) and, to save wasting power unecessarily (and for potential safety reasons as well as saving wear in the rotary generator bearings), the T1154 has circuitry for turning the two PSUs on and off. The HT PSU is turned on by giving it a 6 volt DC feed derived from the LT PSU. Of course turning on the LT PSU is slightly different because it would need turning on before the 6V DC is available so a feed from either 12 or 24 volts DC is necessary. To make full use of these two features the HT and LT outputs from a home brew PSU can be driven from a pair of small control relays. The LT switch-on supply can be provided by a small secondary 12 volt supply built into a home brew PSU if necessary. The Jones Plug carrying these control voltages and LT voltage also provides the input from a second HT supply of 220 volts for the R1155, thus using all eight pins of the Jones Plug labelled "D" on the schematic. It has to be noted that the HT start signal is routed through the 4-pin Jones Plug so that this needs to be wired, not only for Transmit/Receive switch (plus morse key), but for the HT control voltage.

A complication is the 220 volt HT supply for the R1155 which does not have its negative feed connected to the receiver chassis, instead passing through a complicated bias circuit arrangement, which over the years may now include degraded components which can dramatically modify original operating voltages.


 Experimenting with the aerial circuit

I was getting odd results when testing. Ideally I should use a T1154 artificial aerial but, although I have one, it's missing it's dummy load resistors and my only HF ammeter is u/s, so I decided to make a signal detector to see the voltage at the aerial lead. Although I have one or two SWR meters, they're designed for 50 ohms and the T1154 isn't. After playing around with various RF transformers I settled on a small toroid, about a centimetre or so in diameter made from a grey material and painted red. This probably is meaningful but not to me so I checked on the Net and it seems "Red" means Grade 2 Powdered Iron and is good for 250KHz to 10MHz, which is pretty much ideal for the T1154. I wound about 20 turns as a secondary and just passed a heavy insulated copper wire through the centre. The rectified voltage using a small germanium diode at the secondary works fine into a 1mA meter but sensitivity drops right off for the yellow band, so I'll either add an alternative primary winding of say three turns for those frequencies, or maybe just increase the number of turns in the secondary.

 Above a junk box meter fitted with a simple RF detector. The white serrated thing is a 5Kohm potentiometer.
Before I settled on the red toroid, I tried other toroids of different sizes and colours but got weird results. Maximum RF into the lamp and maximum volts on the new meter didn't always correspond and one or two toroids got very hot.

I tried various resistors in my incomplete artificial aerial but then reverted to a 45 watt mains lamp. This worked fairly well on the blue and red bands but I got much better results with a 250 watt mains lamp. The 45 watt lamp has a resistance of about 10 ohms at 240 volts whereas the 250 watt lamp is about 250 ohms. I'll try a 150 watt mains lamp next. I guess for optimum testing I'll need two different lamps. When I finished for the day I'd got about 80 watts CW output at 400KHz and around 40 watts CW on the HF bands.

 Opposite is an interesting feature that can easily be overlooked. The pins should be fitted with a connector which is used to alter the output matching impedance on the Red Range so an aerial having a high reactance or resistance be used.
The 3-way connector (non-shorting or shorting) either leaves the transmitter tank coil floating (non-shorting or normal setting), or grounded through a pair of condensers totalling 30pF (shorting for a problem aerial).



No doubt correct connectors are available but, as most T1154 ancillaries come at horrendously high prices, junk box-based alternatives need to be made. The aerials used on the T1154 are not what most amateurs are used to. Both the fixed aerial and the trailing long wire have indeterminate impedances and do not use standard co-ax plugs. The HF and MF outputs each have a single brass pin which is about 4.5mm in diameter (probably 5/32 inch). In my junk box I found a 2 inch piece of duralumin tubing which was a snug fit so I tapped both ends 2BA and cut it in half. After fitting each with a solder tag secured with a short 2BA screw I now have a pair of mating aerial connectors. Adjacent to the pair of aerial connectors is an earth pin having the same diameter. I used a small piece of brass tubing, and enlarged the hole to about 5/32 inch internal diameter, then cut a slot and squeezed this so the tubing was a snug fit. Next, the HT supply. This uses a special connector comprising a single pin similar to the earth pin plus a polarising pin of about 0.13 inch diameter. To make suitable lead for the HT connection I made a connector identical to that of the earth connector. Next I found a quarter inch plastic rod and drilled it with a hole to fit the polarising pin. I then cut the rod to about an inch and a half and tapped the end to 2BA. What about protecting the lethal voltage on the new connector from the transmitter operator? I found an old relay fitted with a removable square cover which I drilled to accommodate the tapped end of the plastic rod. The HT lead was routed out the bottom of the cover after drilling a hole to match the HT cable.


HT Connector: On the left the plastic rod drilled longitudinally with a hole 0.13 inches in diameter and the end threaded 2BA to be fitted with a plastic nut. The brass fitting is drilled 0.16 inches and the end tapped and fitted with a 2BA scew and solder tag. Centre is an old relay cover. the top is drilled for the plastic rod and a hole is drilled for cable entry on the lower side.

Wiring up the new Jones connector was straightforward. I used heavy cables for the LT leads and high voltage cables for the remainder of the leads. I used a tie wrap to secure the wiring then fitted the cover using heatshrink sleeving where the cables came through the cover. Ideally the connector covers should have 90 degree cable exit but I was only able to get types with a straight through cover.

The socket is labelled "D" on the schematic. The pins correspond to the numbers on the moulding and have the following connections:-

1 220V minus; 2 220V plus; 3 Start LT PSU; 4 12V/24V for PSU start relay; 5 LT minus; 6 LT plus; 7 1200V minus; 8 Start HT PSU

I fitted heatshrink sleeving over the solder joints. The inner surface of the cover is well insulated.

I tried the two new connectors and discovered a strange problem. The mode switch knob hit the Jones plug cover (and if it had passed this it would even foul the new HT cover which doesn't protrude anything like as much). What was wrong?

After puzzling over the problem I noticed the original connector securing bar posts matched the new Jones plug cover (the securing bar itself is missing) so it's pretty clear that the problem is not the plugs. In my T1154 example the wavechange knob and the mode switch knob are identical. Both are moulded with a pointer at right angles to the knob body. I decided to look at pictures of the T1154 on the Net and found that the knob fitted to my example was wrong. In fact many sets used black coloured knobs of the same shape as the coloured types used for the coil tapping switches for both the wavechange and the mode switch. Maybe some have the wrong knob fitted to the former? Certainly mine has the wrong type fitted to the mode switch. The solution turned out to be simple. I have two R1155 receivers and both use the same knob that's used on the T1154 mode switch so I swapped the one on the R1155 wavechange switch for the one on my mode switch... easy? Not so because the mode switch itself has no end stops. Instead, the end stops are built into the front panel and I'd inadvertently turned the switch shaft without the knob being fitted. I did this when looking for a replacement knob to see if there was significant turning resistance. The switch has at least 12 positions when the knob isn't fitted... of which only 6 positions are valid. Time to peer at the circuit diagram and figure out exactly what the switch does...

The mode switch is a Yaxley style thing fitted at the rear of the T1154 and connected via a long quarter inch rod which passes through the front panel and drilled for a pin which mates with a slot in the back of the knob. The knob can be fitted in either of two positions one of which is correct and the other wrong, so putting the knob back on with the switch 180 degrees out might blow up the transmitter. I pictured a big flash from the PT15s so it was vital for the correct orientation to be found.

The switch uses three wafers with contacts at the front and back sides of each wafer. The wafer sides are labelled in the schematic as F, G, H, J, L and M which appear to have (at least) the following functions:-

F & G: each has 2 wipers and 2 contacts wired in parallel for switching LT to the PT15 filaments.

H & J: 2 wipers and 2 contacts, Start LT; 1 wiper and 3 contacts for PT15 bias setting and MCW

L & M: 2 wipers and 5 contacts, microphone switching; 1 wiper and 3 contacts, sidetone to R1155 headphones (Pin 6 on plug A)

Using this information I was able to set the switch to OFF position and fit the replacement knob only to discover it didn't work! It seems the T1154 knobs are a different shape to those used in the R1155, and I had to cut off part of the R1155 version so the switch can select all of its six positions instead of just the three centre ones.



 Above shows an R1155 knob above the knob fitted to my mode switch. The lower knob was correctly used on the T1154 wavechange switch but a second identical one was fitted to the mode switch which was fine until correct Jones Plugs were fitted then it was too long and fouled the Jones plug covers. The R1155 knob, of which I had a spare is not right either because as you can see above those on the T1154 do not have a flat underside. To operate correctly due to protruding end stops the underside needs to be cut back like the T1154 wavechange switch above. As the knob is made from solid material I was able to cut it back by about 5mm to match the shape of the proper knob. It then fitted and worked properly.

 The keying circuitry

The method of switching the T1154 to transmit can be puzzling as it's not carried out with a single connection. The wires involved are carried on the 4-way Plug B which is labelled on the schematic as follows:-

13 Key; 14 Keying relay contact; 15 Earth; 16 Phones. The polarising pin is between Pins 13 & 14.

Jones Plugs numbering is very odd. The 8-way is straightforward and logical with pins marked 1 to 8....... but why is the 4-way numbered 13 to 16?

The Transmit/Receive relay is driven to Receive from an indeterminate position when LT is applied and the mode switch is in any position except "OFF". Then, if the Keying relay contact Pin 14 is grounded to Pin 15 you'll hear the Transmit/Receive relay clonk over to the Transmit position. In this situation, with only Pin 14 grounded, the HT current meter will read zero milliamps because the PT15s are heavily negatively biased. Then, if Pin 13 (Key) is grounded to Pin 15, the cut-off bias to the PT15s is removed and you'll register current on the meter. To transmit therefore, you need to switch both Pin 13 and Pin 14 to ground. I propose to do this by connecting these pins to a double pole centre-off changeover toggle switch. The switch will give me Transmit in one setting, Receive in the centre and Transmit with a morse key in the other position. In this setting the morse key will be in the Pin 13 wiring leg.

For a full setup, including the R1155, Pin 16 carries audio from the microphone amplifier (V4). The microphone pressel switch merely turns on the microphone rather than switching the T1154 to transmit.


 Odd Connectors

 In a little box that came with the Gumtree T1154 I found some strange looking connectors which turned out to be for the high voltage lead and the aerial. Pictures below...

 The high voltage female connector that fits the T1154, on the left is coded 10H/425 and the spare male connector is coded 10H/430 as you can see.

 The right hand connector is fitted to the T1154 chassis and carries a smaller pin which is not used to carry current but is merely a locating pin for the detachable connector.

I suppose the high voltage connector metal shell (on the left) should ideally be connected via a grounding lead for reasons of safety in the event of a short between the shell and the centre socket.

 This is the aerial connector coded 10H/319 which plugs into an aerial socket on the side of the T1154 as shown below.

The metal centre socket just floats in the bakelite case and clearly there's no provision for more than a single aerial wire which enters via a small slot (just visible on the left) in the end of the case.


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