RECEIVER MARCONI R1155
RESTORATION (Jan – Aug 2006)
(DIARY)
References:
1. A.P.2548A Vol I
2. Miscellaneous articles on restoration
Restored unit R1155 Ref No 10D/98 Serial No 32343modif. to R1155A Ref No 10D/820
Will be restored to its original state
1. Initial condition
2. Objective
3. Restoration
4. Aligning and final check
5. Accessories
1. Initial condition
The receiver was very close to its original state with untouched direction finding circuits (only D/F valves missing).
The following discrepancies were found:
A transistorised output stage was built on a PC card fixed to the oscillator shield. The stage was connected to the output transformer, speaker connector, + HT and ground.
The Jones connectors were covered with a panel with a hole for the power cable, connectors for a speaker and antenna/ground.
The power cable was soldered to the back of the Jones connectors.
The wire from the output transformer to the phones was unsoldered in both ends.
Valves V1, V2 and V9 in the D/F part were missing.
Some ventilation holes were drilled in the case and it was badly repainted on the inside.
The scale around the tuning knob was missing (I later found out that there had never been one, no holes were drilled for it, and according to the article Tuning for Perfection in Radio Bygones nr 45 it was not used on later models with the type 13 tuning device).
The separate power supply following the receiver was a rather dangerous design without full transformer and giving high potential on the chassis. It also gave very high HT until the filaments were warm.
2. Objective
I decided to restore the receiver to the original state in every detail and with working D/F. Power supply, power amplifier and speaker should be external. I also decided to get a D/F indicator and a morse key of the Lancaster type. Finally I decided to make an aerial plug board similar to the one used on early aircraft before the aerial switch was introduced, and also to get a complete set of spare valves.
3. Restoration
The restoration plan comprised the following steps:
Cleaning the panel and screws
Removal of the transistorised AF power amplifier, will be replaced by external computer speakers with built in amplifiers
Procuring the D/F valves, 2xVR99A and 1xVR102.
Removing the external power cable from the back of the Jones socket and the panel in front of the sockets.
Repair of the ventilation holes and repainting of the case.
Rebuilding of the external power supply.
Alignment.
Final check, listening check.
Procuring a D/F indicator and wiring and testing it. Make a suitable loop antenna for MF listening and D/F.
Making an antenna plug panel.
Procuring a "bathtub" morse key.
Procure a complete set of spare valves.
3.1 Basic restoration
The power supply was tested with dummy load on the HT (lamp 220V 15W). The resistance of the power inputs of the receiver was measured between them and to the chassis. The "smoke test" showed that the receiver worked quite well on all bands. The LT was 6.6V, the HT only 140V at 90 mA. The phones output did not work (060113).
The PC board with the power amplifier was removed. The wire for the phones was connected in both ends. The receiver was tested again and now the phones worked and the HT was 235V at 60 mA! (060114).
The panel was washed with soap solution, some screws with rust remover. The tuning knob and the scale panel section were removed and the scale, pencil scale and plexiglass were cleaned with soap, like new! The cork in the fine tuning was also cleaned and glued to its plate and everything was reassembled. The tuning worked very smoothly after this. The case was cleaned with a vacuum cleaner and soap solution (060116).
The power cable was removed from the back of the Jones socket and connected to the front instead. As I had no Jones plugs I used car connectors as an intermediate solution. I bought a pair of computer speakers with internal amplifier and connected them and the phones with car connectors. After connecting an outdoor antenna the receiver worked very well with both phones and speaker. LT was 6.3V, +HT +200V and -HT -40V (060117).
3.2 Rebuilding the power supply
The power supply was very hasardous, HT was taken directly from the mains without a transformer. Until the receiver was warm there was also 350V HT. The power supply was completely redesigned while using as many of the components as possible.
Two new toroidal transformers were used, one 7V for the LT and one 2x120V for the HT. Two lamps 380V 15W were added as dummy load to even out the difference in HT in idle, no D/F and D/F modes. A chain of zener diodes 2x56V was connected over the HT output to limit the HT to 230V. A switch was also added in the HT circuit so I can switch it on after a 15 second warmup time.
The redesigned power supply was first tested with dummy load, then with the receiver. The D/F valves were not used yet, so some of the dummy load had to remain. LT was 6.3V, HT 220V (+185V and -36V). Ripple 4Vptp on the LT, 80 mVptp 100 Hz on HT. In idle the maximum was 245V. The receiver had specified voltages and worked very well (060209).
3.3 Measuring the resistances and voltages in the receiver.
The total resistance from +HT to ground and +HT to -HT showed resonable values. Resistors and decoupling capacitors were measured in their circuits. Because of parallell connections they do not show nominal values but some simple calculations indicated good values. The valve voltages were measured on band 2 and 5 with a coarse check on the other bands. All checks with AVC off and for volume control min and max. All voltages were inside +-10% except a few just outside that tolerance, as compared to the values in manual A. P. 1186. Looked very good (060211).
3.4 Check of the IF curve
The IF curve was measured in the following way: The signal generator with a counter in parallell was fed to the mixer grid, V4 top cap, over a 1/100 damping network and a 1000pF capacitor. Signal generator output 560 kHz with internal modulation 400 Hz 40%, output 0 dB. The main oscillator was stopped with a 20 nF capacitor from C35/F.S.zf to ground. The output was measured with an AVO-meter on the phones output. The receiver master switch was set to OMNI and the volume was set to 8Veff at curve maximum.
The frequency was varied from 552 to 562 kHz in 1 kHz steps and the output was noted. Umax was at 556,6 kHz, that is the IF=556,6 kHz (spec. 560). Bandwidth 5 kHz at -6 dB (spec. 4 – 6 kHz). The curve was even and symmetrical. The sensitivity was measured to 45 mV/1000 (with input damping 1/1000), after correction for the loading of the damping network with factor 0,6 the sensitivity at the mixer input is 27 uV for 15 Veff out, ca 50 mW. The IF stages seem to be in very good trim! (060215).
3.5 Measuring the overall sensitivity
The sensitivity at the antenna input was measured for end and middle points of the scale on all five bands. All bands were better than 10 uV, the lower end of band 1 and 2 showed tendensies of overload, will be checked with looser antenna coupling (060220).
3.6 Direction finding D/F
The D/F valves were inserted and all dummy loads removed. LT was now 6.4V and HT 225V in BAL and VIS (with D/F circuits activated) and 235V in AUR. In OMNI and AVC the HT voltage was 220V as before (060501). The D/F indicator was connected and a D/F antenna was made.
The D/F function was tested and found to work quite well! (060820).
3.7 Painting
The outside of the case was in good condition with deep black wrinkle paint and was left as it was. The case was masked and the inside treated with paint remover. Some dents were flattened. New black paint was sprayed in two coats after priming with a thin layer gray. The outside of the case and the panel were retouched with matte black. I decided to leave the ventilation holes and covered them with small pieces of alu net painted black and glued in place with drops of epoxi. This is of course not as the original but can hardly be noticed and gives a better heat dissipation. After this the receiver looks almost like new!
4. Alignment and final check
After listening tests on all bands I decided the receiver was in very good trim and that furher alignment was not needed.
5. Accessories
5.1 Procurement
The following accessories were procured via eBay:
D/F indicator
"Bathtub" type morse key
WWII phones
Jones connectors (straight type)
Pins and securing bracket for the Jones connectors
Set of spare valves
Connectors and cables for the "aerial plug board" were bought locally.
Computer speakers with built in amplifiers were bought locally.
5.2 Panel for D/F indicator, aerial plug board and speakers.
A simple chassis was made of plywood and painted black. Speakers and D/F indicator were mounted. an antenna panel was built with a sheet of pertinax and TV connectors with a layout resembling the Lancaster aerial plug board (060502).
5.3 Jones connectors
The power cable was connected with an 8-way straight Jones connector, may be changed to a C-type connector later (060501).
The D/F indicator was connected over a similar Jones connector and a microphone plug for simple disconnection (060503).
5.4 D/F antenna
A simple loop antenna was made by two crossed thin teak boards 70x2x0.8 cm. The winding has 9 turns and the coupling coil 1 turn. A 2-gang capacitor variable from 30+30 to 520+520 pF is used. This circuit is resonant at 500 to 1700 kHz, the MF broadcast band. The loop is connected to the receiver D/F input with a 4-pin Jones socket (060820).
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Updated October 14th 2009