INTRODUCTION
The T1154 transmitter and R1155 receiver require power supplies when used in aircraft or sea craft, to convert the input voltage to the required voltages for the installation. They are usually of the rotary transformer type. There are two main types. One power supply (called HV) generated the transmitter plate voltage (1200 volts at 200 mA). The other power supply (called LV) generated the plate voltage (220 volts at 110 mA) and the valve heater voltage (7 volts at 13 A). These two power supplies, were available in 12 volt or 24 volt input voltage versions, to suit the battery accumulator voltage in the appropriate craft. During their life, the power supplies were modified to cater for a navigator operated receiver, and these supplies had the letter “A” added to their type number as a suffix. The power supplies went through several modifications during their life.

	HT	HT	LT	LT	LT
12 v input	type 32	type 32A	type 34	type 34A	type 34X
24 v input	type 33	type 33A	type 35	type 35A	-
Output voltage	1200 v	1200 v	220 v 7 v	220 v 7 v	245 v 8 v

Table 1: Power Supply Types

Picture 1: High Voltage Unit (Type 32A)

Picture 2: Low Voltage Unit (Type 34)

MECHANICAL DESIGN
The power supplies were each in a long steel case, which was identical in size and weight, (16.5 inches long, 7.625 inches wide, 6.375 inches high, 27 to 30 pounds weight). They slid into a cradle and were secured by two screws. All the cables were on the front end, so the supplies were easy to change for servicing. The only visible difference was the number of cables attached, and the nameplate. Each plug has a physical means of holding them in place, a post and clamp for the small ones, and a screw for the large one. Inside the case, is a large heavy rotary transformer. There is a fan on the rear end that draws air through a gauze window. At the front of the case, are the connectors and the start relay. Along the top of the rotary transformer are the large filter chokes, wound on paxolin tubes with heavy gauge cotton covered wire. The oil filled filter capacitors are arranged throughout the case. The actual rotary transformer inside each power supply, had a model number, that is very similar to the power supply type number, and this may cause confusion.

Type	32	33	34	34X	35
Stores Ref.	10K/17	10K/18	10K/19	10K/61	10K/20
Transformer type	28	29	30	30X	31
Stores Ref.	10K/21	10K/22	10K/23	10K/63	10K/24

Table 2: Rotary Transformer Types

There are nipples on each of the rotary transformer bearings, but these are for oil and not grease. Hence there was a leaflet produced that required these to be replaced by felt plugs. They required 5 drops of oil for every 30 hours of flight.

ELECTRICAL DESIGN (HIGH VOLTAGE SUPPLY)
The electrical design is very simple. The power enters through a large main connector, and goes to the start relay. There is a capacitor to chassis on each pin. The connector (Type 171) has 2 pins and a locating post that holds the connector in place, and also ensures the correct polarity connection. The power then leaves the relay and goes through a 3 section RF choke to the rear of the rotary transformer, to the brushes. Each power lead uses large heavy gauge wire, and large chokes. The positive lead uses chokes L1 and L3 (on the same former) horizontally along the length of the case, and choke L5 vertically at the rear of the case. There are capacitors C3, C5 and C7 at the choke junctions. The negative lead is the same design, using chokes L2, L4, L6 and capacitors C4, C6, and C8. Note that neither the positive or negative leads are connected to ground or chassis. They are direct connections as they carry heavy current. However, the capacitors are connected to chassis, and so is the frame of the rotary transformer. The capacitors are 2 uF or 4 uF oil filled type.

AP1186 shows the RF input choke as 3 separate chokes. All power supplies I have seen have been modified to a 2 section choke. The capacitor C5 has been rewired to be in parallel with C3 (effectively 6 uF), and similarly C6 has been rewired to be in parallel with C4. This means that L3 and L5 are in series, and also L4 and L6.

The rotary transformer is an open frame type, wound on a common armature core, with a low resistance shunt field. There is a small series field winding to reduce the input curent surge. The rotary transformer efficiency is 60 percent. The 1200 volt high tension output goes through a filter to the output. It consists of C9, L7, C11, L9, C13, and C15 to a fuse then to the single pin output connector P3. The negative lead from the rotary transformer is similarly filtered by C10, L8, C12, L10, C14 and C16, and connected to pin 7 on the 8 pin connector P2. The 6 pin connector P1, is connected pin for pin to P2, and is a pass through for the low voltage power supply. The “A” models have an extra socket SK2, which provides voltage output when the high voltage start relay is activated. This is for use in installations with an extra receiver.

Figure 1: HT Circuit

ELECTRICAL DESIGN (LOW VOLTAGE SUPPLY)

The electrical design is the same as the high voltage supply, except there are 2 output windings and brush sets on the rotary transformer, one for the receiver HT and one for the valve heaters (LT). The power enters through the large main connector, and goes to the start relay. The power then leaves the relay and goes through a 3 section RF choke to the rear of the rotary transformer, to the brushes. Each power lead uses large heavy gauge wire, and large chokes. The positive lead uses chokes L1, L3 and L5. There are capacitors C1, C3, and C5 at the choke junctions. The negative lead is the same design, using chokes L2, L4, L6 and capacitors C2, C4, and C8. The positive and negative leads are not connected to ground or chassis. They are direct connections as they carry heavy current. The capacitors are connected to chassis, and so is the frame of the rotary transformer. The capacitors are 2 uF or 4 uF oil filled type.

The 220 volt high tension positive output goes through a filter to the output. It consists of C8, L9, C11, L11, C13, C15, L13, and C14, to the pin 8 on connector P1. The capacitors go to chassis, except for C13 and C14, which connect to the negative lead. The negative high tension output lead from the rotary transformer is similarly filtered by C9, L10, C12, L12, C13, C16 and C14, and connected to pin 7 on the 6 pin connector P1. The capacitors are 0.1uF and 2 uF. Choke L9 and L11 are small air cored RF chokes. Choke L13 is iron cored.

The 7 volt low tension positive output goes through a filter to the output. It consists of C7, L7, C10, and L8, to the pin 12 on connector P1. The capacitors go to chassis. The negative low tension output lead from the rotary transformer has no filtering and is connected to the frame of the transformer, and to pin 11on connector P1. The chokes L7 and L8 are wound with heavy gauge wire. The rotary transformer is an open frame type, with 2 sets of brushes on the output end. The efficiency is 50 percent.

The installations using a navigator’s receiver, require a modification (“A” models). The oval gauze window is cut away and a 1pin socket (SK2) and a 4 pin plug (P2) is fitted. Behind this is a resistor and a relay. The 4 pin plug provides power to the navigator’s receiver. A resistor (0.1 ohm) reduces the heater voltage to the correct value. The 1 pin socket is connected to SK2 on the HT supply. The relay turns off the navigators receiver HT, when the transmitter rotary transformer is running.

Figure 2: LT Circuit

INPUT VOLTAGE

The input voltage to the rotary power supplies will vary, depending on the charge state of the accumulator, and if the aircraft engine is running (thus charging the accumulator). When the input voltage changes, so will the output voltage to the transmitter and receiver. The voltage variation to the HV rotary supply, will change the HT voltage to the transmitter, and will change the power transmitted. This is not critical. The voltage variation to the LV rotary supply, will change the HT voltage to the receiver, and change its performance slightly. This is not critical. The voltage variation to the LV rotary supply, will also change the heater voltage. The heater voltage must be maintained between 6 and 7.8 volts, or the valves may be damaged.

There was a resistance unit fitted between the accumulator and LT rotary converter, which is switched in and out, to control the input voltage. Resistance Unit Type 47 was used for 12 volt systems, and Type 52 used for 24 volt systems. When charging the accumulator, the resistance unit is in circuit. When not charging the accumulator, the resistance unit is switched out of circuit. The manual mentions that the resistance units must be well ventilated. The current requirements of the Type 33 and Type 34 power supplies, can be between 10 to 30 Amps. The low voltage cable size and length affect the voltage drop, and the voltage at the rotary transformer input terminals. Therefore the resistance unit must be set for each individual installation. The starting current is in the order of 100 Amps. The adjustment procedure, is to measure the accumulator voltage (on charge), measure the heater voltage at the transmitter, and the resistance is then adjusted to provide 7.5 volts at the transmitter. There is an auxiliary switching relay, which will switch the resistance unit into circuit, when the accumulator is being charged. It is a Type 219 for 12 volt systems and Type 220 for 24 volt systems. The manual mentions that it “should be mounted where it is not likely to experience much vibration as it is not very robust construction”. Note the LONDEX relay in Figure 3 Cabling Diagram. When used in a system with an “electrical cut out” in the charging circuit, the resistance unit is switched in and out automatically. When used in a system with a “self regulating generator”, the resistance unit and relay are not required. The manual warns that this “is liable to shorten the life of the valves”. When used with the older Type 34X rotary supply, “the input was boosted by switching in and out of circuit, a 2-volt 20-AH accumulator“, depending on the voltage due to charging or otherwise. This was a manually switched system. The manual also states that after any flight with an “emergency connexion” then “all the transmitter and receiver valves should be replaced”.

Figure 3: Cabling

Figure 4: Wiring

HIGH VOLATGE UNIT RESTORATION

When received, the HV power unit was complete, but very dirty, and missing the top cover. It was cleaned thoroughly, the bent parts straightened, and the outside repainted. The inside was not repainted. A new cover was made. The wiring was checked off against the circuit, wire by wire. It was complete with no wiring changes. This model has the modification for 2 receivers so it is the Type 32A. Each component was measured and checked for value. All the joints (especially in the high current path) were tested for low resistance. So were the joints to chassis for the RF filters. The bearings were lubricated, and checked for free rotation. The brushes were removed and the commutator cleaned and burnished. It was checked for short circuits.

I had no input plug, so a temporary input cable was attached and routed out the HT connecter hole. Power was applied, and nothing happened (which was good). Next, some jumpers were arranged with a small toggle switch, to connect power to pins 5 and 8 on P2. Power was applied again, the switch thrown, and the start relay clunked in. The 12 volt path was checked, all the way to the brush holders. It was powered down. The low voltage brushes were fitted. It was powered up, the switch thrown, and it started to rotate, quite loudly. The bench power supply groaned quite a bit. After some erratic running, it settled down to a steady spin. Everything was checked for heat. Several starts and stops were performed until I was confident. The high voltage brushes were fitted, and the unit powered up. It produced the 1100 volts DC, but not at the output, as one of the chokes had gone open circuit, since measuring. It was fixed, just a broken wire at the solder joint. All capacitors, chokes and wiring (and the rotary transformer and bearings) were checked for heating. A resistive load was connected, and run for a period, to test for heating under load.

Picture 3: HT Original Condition

Picture 4: HT Inside (after restoration)

LOW VOLTAGE UNIT RESTORATION

The restoration of the low voltage unit was a little more difficult, as I only had the rotary transformer. I had a case made, and located the parts required from the junk box, the oil filled capacitors, the heavy wire, and the connectors. I had to make the 2 large LT chokes, and the 2 small HT chokes. I purchased a 12 volt relay capable of switching 200 Amps.

Picture 5: LT Rotary Converter

Picture 6: Empty Case and Capacitors

I greased the bearings of the rotary transformer, and powered it up. When I was happy with the performance, I bolted it into the case. I added the capacitors and chokes, and wired it up as per the manual. I used a resistive load to test the high voltage and low voltage outputs, under load.

Picture 7: LV Unit Inside (after construction)

CABLING

The cables were made up. The junk box provided the Jones plugs. The Jones plugs are fairly easy to find, perhaps the transmitter high voltage plug being a little more difficult. The HT unit requires three
6 pin female (HV to LV)
8 pin female (HV to T1154)
1 pin female (HV to T1154)

The LT unit requires one
6 pin female (LV to HV)

The wiring and plugs for a second receiver, were not required.The main input plug for the voltage in is a Type 171 connector (10H431), is rather rarer and much harder to locate. It is a large 2 pin female plug, with a third hole to allow it to be screwed on, and provide the correct polarity.

Picture 8: Dyno Plug (Type 171)

Picture 9: Dyno Plug (Type 171)

The wiring between the units and the T1154 can be made up of multi-core cable. If none is available, you can use the multi-core cable used for wiring up car trailers, available from automotive shops. Use the largest available. The heaviest requirement is for the heater wiring of 13 Amps, so 2 wires can be paralleled if required, for both the heater and earth return. Alternatively, you can use individual wires, and cover them with heat shrink tubing. The HT wiring to the T1154 can be made up of thick coax cable which has a high insulation covering, and only requires 1 wire. The input power should be capable of 30 Amps, so 2 heavy wires should be used. These can be found in an electronics shop, from the wire intended for solar installations, battery chargers, or heavy speaker cable. These cables require heavy lugs on the ends connected to your power source. I found that during testing, my connectors got hot, and the cables became warm and floppy, so I upgraded to heavier cable and connectors. There was also a 1 volt drop between the power source and the input connector, and also between the input connector and the rotary transformer brushes. Evidence of the voltage drops expected was noted from reading the LT rotary transformer nameplate. The HV rotary transformer is less critical.

LT Rotary Transformer Nameplate
Input 9.3V 23A,
Output 7.2V 13A,
Output 225V 0.11A

HT Rotary Transformer Nameplate
Input 12V 32A,
Output 1200V 0.2A
HOOVER LIMITED

PERFORMANCE

The load was varied and the results graphed. The input voltage was measured at the input terminals, and kept constant during measuring. Several load curves were drawn for various input voltages, from 10 to 14 volts. Also, the input current was plotted for the 14 volt input case. The HT no load current was 12 Amps at 14 volts input, rising to 32 Amps, at full output load. Note that the output voltage can sag up to 300 volts.

Figure 5: T1154 HT Performance

The low voltage unit was also tested with a resistive load. The LT load was several 1 ohm 300 watt resistors, which were connected in series/parallel to provide the appropriate current load. The HT load was a large potentiometer in a box, with 2 built in meters. The HT and the LT were plotted separately. The LT conditions of 7 volts at 13 Amps was met, with a 10 volt input at the unit terminals. The HT voltage for that same 10 volt input was 220 volts at 100 mA.

Picture 10: R1155 HT Testing

Figure 6: R1155 HT Performance

Picture 11: Testing LT

Figure 7: LT Performance

CONCLUSION

Both power supplies are featureless heavy black boxes. They contain a rotary transformer and filtering. I have tested the 12 volt versions, and provided performance curves. The 24 volt versions would have the same characteristics, but draw approximately half the current, and be more tolerant of cabling and connectors. The regulation is in the order of 18 to 25 percent. The variations in LT voltage are a problem, as is recognized in the manual text. The control of this LT output voltage by changing the input voltage (at high current) is not very elegant. An inbuilt regulator of some design would be more beneficial, and perhaps increase the life of the valves. It would be wise to have an earth strap between each unit and the transmitter (and connected to earth), not only for the RF present, but as a safety precaution in the possible case of a broken wire or poor connection in the 1200 volt circuit. These power supplies are not very common.

REFERENCES

Air Ministry Publication, AP1186, Vol. 1, Sect. 1, Chap. 7

Copyright
Ray Robinson

INDEX