RESTORATION (2006 to 2009)
(DIARY)
References:
1. Luft-Boden-Einheitsempfänger E 52 Prüfung, Reparatur, Abgleich
(Conrad H. von Sengbusch & Ulrich Wintzer) Part I and II
2. Der Empfänger E52a Ausbildung am Gerät
See link below.
Restored unit Köln E 52a-1 Ln 21000-4 serial nr 774
(a simplified "a" model, with motor tuning).
To be restored to model E 52b-1 in Luftwaffe colors
(dark greyish black, without motor tuning and some test buttons).
1. Initial condition (summary)
2. Objective
3. Disassembly
4. Inspection (detailed condition)
5. Module restoration
6. Assembly
7. Function test, alignment, final test
1. Initial Condition (summary)
After ”modernizing” in the beginning of the 1960´s:
- Case painted in grey hammer paint, scratched, small dent,handles missing
- Chassis painted the same way, scratched, crystal precipitation
- Panel painted in a greyish plain paint, small scratches, extra holes for
calibrator and S-meter, the plate around the dial in hammer paint,
the same holes, no color on the frequency range plate
- Motor drive for the frequency range and tuning removed
- RF1 rebuilt with 6AK5
- RF2 rebuilt with 6AK5
- IF original
- OSC original, MIX rebuilt with 6X8
- BFO and DET original- AF rebuilt with 6CL6
- Power unit original
- Tuning unit original except for the motor drive
- Crystal calibrator and S-meter added
- Some coils in bad shape, extent unknown
- The tuning capacitor badly aligned since disassembly in the 1960´s
Measured values before disassembly of connection between the three capacitor units:
Max/min capacitance max minC144 ariel circuit 406 23 the dial 4 mm counterclockwise
C145 RF1 in 388 25 -,,-
C146 RF1 out 394 25 -,,- + loose stator
C147 RF2 in 535!! 22
C148 OSC 394 30 the dial 2 mm clockwise resp. exact!
C149 RF2 out MIX in 383 20
Measurements with the oscillator capacitor at 40 pF
C144 25
C145 28
C146 27C147 25
C149 26
Conclusion: Very poor function and alignment.
2. Objective
- Restoration of the dark grey original color on the case, chassis and panel and
handles close to the original. Panel markings close to the original
- Original or original looking knobs
- Restoration of RF1 och RF2 close to the original with RV12P2000
and relay R1 for calibration check
(base and components as close as possible, wiring original)
- Restoration of MIX with RV12P2000 (see above)
- Restoration of AF with RV12P2000 (see above)
- Removal of the crystal calibrator and S-meter (possibly used as free standing units), obs filling of the panel holes
before painting
- Check of the variable BFO and restoration if necessary
- Restoration of all coils and cores to alignable state
- Restoration and basic adjustment of the tuning capacitors
- Alignment to specification
- Final checkout, listening checkout
The motor drive will not be restored. Cover plate for the D/F connector to be manufactured like the original. The receiver will then be like the E 52b-1 internally and functionally.
3. Disassembly
To facilitate repainting all blocks were disassembled according to the description in ref 1 part II. Before the tuning unit and capacitor were disassembled the alignment of the 6 capacitors and and the three capacitor blocks were noted (see par.1):
Wiring of the tuning capacitors to the ceramic plinths:
C144 stator 35 rotor 34
C145 36 38
C146 44 42
C147 45 47
C148 front back
C149 55 57
Photos were taken of the modules and some of the wiring between the modules RF1, RF2, OSC/MIX and AF before restoration.
4. Inspection (detailed condition)
Block Remark
RF1 Marked with red 3237
original W3 W7 C153-56
new W4 2k W5 900 W8 15k C152 50n 250/750Rö2 RV12P2000 Valve socket (Relay R1)
RF2 Marked with red 1846
original (W11) W12 W15 C158-60 (C353) C354
new W13 900
W16 15k W103 100k 0,5W C267 0,1u 250/750
Rö3 RV12P2000 Valve socket
MF Nr 6376 stamped into the chassis and case.
Minor crystal precipitation.
The alignment cores seemed turned! The S-meter connection was desoldered during the inspection.
original everything except the following 2 cap.
new C193 0,1 u 250/750 (original still there) C190b 47p
OSC/MIX Marked with red 2613
OSC The oscillator is all original except W20-21 2k (U9 in place)
MIX original W22 (W23) W24 C165 C166-68 C169 C170 (U10 in place)
new W25 90k
W26 15k
Rö6 RV12P2000
Valve socket
DET/BFO Marked
Seems to be untouched. Minor crystal precipitation.
AF Marked with red 2362
original Socket for Rö12
new W72 100k W73 1M W74 80k W76 250 W82 1k
C245 50p 400V
C246 0,1u 250/750 C247 200p 250 C249 1u 120 C250 10n 110 C251
10n 110
D20 D21 output chokes
Ü1 output transformer Rö12 RV12P2000
Coil unit Marked with paint 2925. L1 core missing. L2, L3 and L5 OK.
RF1 L4 core bad. All cores movable, trimmers seem OK. All cores out of alignment.
Coil L7 missing entirely! Should according to note have 28 turns. The other coils seem OK. All cores out of alignment.
Coil unit Marked with color 2933. L16, L20 and L29/30 missing cores.
RF2 1 small capacitor changed.
Coil unit Marked with paint 2849. Everything clean. All OSC coils seem
OSC/MIX as well as all components seem OK. Probably realigned.
MIX coils seem OK as well as all components. Probably realigned.
Tuning- Corse tuning is hard to move. Needs cleaning and och
unit lubrication.
The oscillator capacitor C148 capacitance 22 – 386 p, perfectly aligned with th corse scale
end points!!! Dial lamps changed to screw socket.
Tuning capa- Almost all adjustment screws and ceramic pins not movable on C144-147 and
citor C149. Seem very badly aligned, C144 and C147 show very high
max capacitance. Hard to turn.
Power- Very good original condition. Some crystal precipitation. Rö 13 base somewhat damaged. Nr 1764
supply stamped on the chassis and case. Red stamp ”Lehrenhaltig".
The case marked with pencil 860.
Chassis Gray hammer paint, loosening, scratched, crystal precipitation. Surfaces that should be in contact
with modules are painted. U16 and U31 test buttons exist, otherwise empty holes. Marking on the
right shelf of the left compartment in white colour, was partially lost when paint was removed
…9398 ??
Panel Gray plain paint, yellowed, some scrathes. Hole for S-meter, switch for crystal calibrator
and phone connector. Red screw markings overpainted. Marked 986 with pencil on the back.
Case Gray hammer paint, scratched and with small dents. Handles missing.
Missing components:
Resistor Dralowid green 0,25 W
250
900 2 each
1k
2k
15k 3 each 1 orig. found
80k
90k orig. found
100k
1M
D:o 0,5 W
100k
Capacitors
50p 400V
200p 250V
10n 110V 2 each
50n 250V
0,1u 250V 2 each
1u 120V
Chokes D20 D21 and output transformer Ü1
1 valve RV12P2000 and 3 sockets (bought 5 + 5)
Original knobs (large knob for fine tuning is orig.)
Handles for case
5. Restoration of modules
5.1 Disassembly
The restoration started with the removal of all non-original parts from RF1, RF2, OSC/MIX and AF (051115).
5.2 First restoration!!The assembly started with fixing the socket for valve Rö12 in the AF module!!! (051122). See photo!
5.3 Tuning capacitors C144 – C147 and C149
The tuning capacitor C144 – C147 (4-gang) was restored and adjusted (051127):
Treated with rust removal and loosened all adjustment screwes and ceramic pins. Exercised and lubricated. Bent the plates somewhat on C144. Loosend 4 screwes and adjusted the stator on C144 and C147 for lower max. capacity.
Adjusted all to 34 pF. C147 master, others measured and adjusted against it.
Result C147 C146 C145 C144
min 19 21 21 18
34 34 34 35 34
50 50 50 51 49
100 100 101 101 100
150 150 150 151 150
200 200 200 202 201
250 250 249 252 252
300 300 299 301 301
350 350 349 348 349
max 386 387 384 385
max deviation +2 +2 +2
-1 -2 -1
delta C 367 366 363 367
The tuning capacitor C149 was restored the same way (051127)
Measured min-max-capacitanse was 18 resp. 383, delta C =365.
Cleaned the chassis contact surface, cleaned, blew and packed in plastic bags. Top condition!!
The oscillator C148 was perfect at inspection, 22 – 386 p, perfect alignment with
the end points of the coarse dial.
5.4 Power module
Was cleaned with petrol. Inspected in accordance with ref. 1 part 1 page 12, C? burned out and removed, in function
only with 12V power, to be fixed later. Otherwise OK. The insulation was strenghtened in some places with
some critically sharp corners. The power switch was set at 220V, was changed after the first voltage measurements
to 230V to get a correct filament voltage.
The power unit was first run without the valves just to measure the filament voltage. Result:
Ufil 14.0 V without load
Ufil 13.8 V loaded with 5 W
Ufil 13.4 V loaded with 10 W (+ 6 %) 12.8 V @ power switch at 230V
The valves were inserted in the power supply and all voltages were measured. Result:
Ua 190 V loaded with ca 10 W 184 V @ power switch at 230V
Unoise 1,5 Vpp
Ustab 146 V without load
Ugrid -3,2 V without load
Input current to the power supply was 0,25 A, which means that the input power with cosinus fi 0,9 is 52 W.
The power supply worked perfectly!! (051204).
5.5 RF module 1
Some new resistors were added, a suitable relay was fixed as R1.
All wires were connected, wires to the valve socket were prepared (socket missing). Contacts
treated with Oscillin. (051216).
The valve socket (from NRHF) was fixed in place and the wires connected. Rö 2 was inserted.
The connections were checked. (060311).
5.6 RF module 2
Some new resistors were added. All wires were connected, wires to the valve socket were prepared (socket missing). (051217).
The valve socket (from NRHF) was fixed in place and the wires connected. Rö 3 was inserted.
The connections were checked. (060311).
5.7 Mixer
Missing components were added. All wires were connected, wires to the valve socket were prepared (socket missing).
(051219).
The valve socket (from NRHF) was fixed in place and the wires connected. Spare valve R2 was inserted, OSC/MIX restored! Photos taken of restored modules (060126).
5.8 AF module
The module frame was cleaned. The three connection boards were chosen as close to the original as possible. The output transformer (a replacement without feedback) was fixed to a board.
Replacement components were assembled and all wires connected and fixed. All connections were
treated with Oscillin. The wiring and components were checked.
The boards were documented and photos taken of the restored module 060108).
The cathode resistor was increased to 680 ohm to lower the temperature of the output valve.
A cathode follower output for low impedance Hi-Fi phones was connected via 100 uF över the cathode resistor (060709).
The connector was mounted in the empty hole for the "Kraschtöter"
5.9 Coil modules
The coil units were tested for resonance with a 2x500 pF capacitor, trimmed down to 2x390 pF. Alignment cores were moved to get the ranges 2 – 4 complete, all circuits were resonant.
The cores and trimmers were lubricated with Oscillin. Some trimmers were fixed with epoxy glue (060628).
5.10 Valve testing
A simple valve tester was built and all valves were tested. Rö 6 had no heater current, Rö11
too high anode current, no output signal. The top connector was found to be left in the socket! (060125).
The spare valves, R1 – R7, 4 from NRHF and 3 boxed bought from Germany, were tested (060619).
5.11 Painting
Chassis, panels and dial unit were treated as follows:
All the old paint was removed with paint removal and easy rubbing. The extra holes in the panel were mended with thin metal plates and epoxy glue and rubbed even. The parts were masked and treated with base paint. Final paint was applied in two coates with diluted Servalac Aqua mixed to colour RAL7021. A small part of the original paint was left on the chassis behind the mirror (060624).
The engravings were filled with white paint (texts) and red paint (screw markings). The signs for frequency and raster ranges were created in PowerPoint and copied on high quality photo paper.
6. Assembly
The tuning capacitors were fixed to the back of the painted chassis.
The backplane was treated with Oscillin and fixed to the chassis (060624).
The tuning module was fixed with the tuning capacitors preloaded and aligned for max capacity. The capacitanses were carefully checked for conformity after the assembly (060703).
The coil modules were fixed in place as were the cables from RF1 to RF2 and RF2 to the mixer. The mechanism for the range switch was fixed and adjusted.
The dial window unit was fixed in position and the focus of the photo dial was adjusted (060706).
The RF and OSC/MIX modules were put in place as well as the IF, BFO and AF modules. The power unit was inserted. A first "smoke test" was run. Everything seemed normal and some stations were heard!! (060707).
7. Function tests, alignment, final tests
7.1 Coarse check, coarse alignment
The IF module was checked for correct IF of 1 MHz. The band width regulation seemed to work well. See below for further checks.
The oscillator circuits were coarsely aligned together with the mixer and RF stages for ranges 2 – 4. Range 1 and 5 will have to be postponed until I can find coil components. The alignment was done with signal at the aerial input to include the entire signal chain and the dial in the tests. The frequency was checked with a counter. After this a whole bunch of stations could be heard on all three bands!! (060708).
The BFO did not work. After some experimenting with a suspect capacitor it started oscillating. The signal was a little weak, 15pF was added in parallell with C232. A shaft for manual BFO control was already there, but U19 was not wired. After wiring it according to the schematic a control arm to the switch U19 was added. The manual BFO now worked but was too strong, ca 80Vptp. The wire to the screen grid was moved to the lowest tap on the coil (white point). The oscillator is now working with the same output in manual and crystal controlled, ca 10Vptp. The coil core was aligned for zero beat with the knob in the middle position (060715).
The AVC was checked in A1/A3 regulated. It varied from 0V without signal to -2.2V with a very strong station. The screen voltage was fixed in this case, ca 110V. The check was made on RF stages 1 and 2, seemed OK. A1/A3 unregulated worked like regulated. The fault was traced to missing rectifiers, they had been removed with the motor circuits. Two diodes 1N5408 were instead wired in the power unit to feed the relay voltage. This was 25V unloaded, around 14V with load. Both relay R1 for the calibration check and relay R3 for regulated/unregulated was now working. The volume control now gave a screen voltage from 0 to 80V when in unregulated position. The signal passed from about 10V and reached full volume in a narrow range, perhaps a little too sensitive but fully working volume control. The voltage on the grids was now fixed at
-0.5V (060717).
The sound quality was not very good from the output transformer with old 4000 ohm phones. A connector for modern low impedance Hi-Fi phones was added as a cathode follower output from the output valve over a capacitor of 100uF. This gives a very good sound quality. The connector was fixed in the hole for the ”kraschtöter” under the lid over the AF stage.
The IF module was now thoroughly checked by measuring the IF curve and amplification. Conditions: The oscillator valve was removed and the mixer was disconnected by isolating pin 54 (C165). The signal generator was connected over 27 pF to the grid of the mixer Rö6. Measurements were made with an oscilloscope connected to the cathode follower output on Rö12, probe 10x, no phones connected. A3 unregulated broad with max volume. Uin 100 uVeff (signal generator Trio 540 at full volume in high, external voltage divider 1/1000. Uout max was ca 4.0 Vptp (1.4 Veff) over 680 ohm. Curve:
f kHz Uout V
992.7 0.2 barely visible signal at 990 resp 1010!
993,7 0.5
994.7 1.0
995.7 2.0
996.7 3.2
997.7 4.2 top
998.7 4.0
999.7 3.7 in narrow top 2.5 Vptp (0.9 Veff) at 999.5
1000.7 3.6 0.5 Vptp at 999.06 resp 1000.055, very sharp!
1001.7 3.5 1/5 at +- 400 Hz
1002.7 3.3
1003.7 3.0
1004.7 2.0
1005.7 1.0
1006.7 0.4
1007.7 0.1
Fine alignment can wait as the IF curve looks rather good.
Amplification mixer + IF + AF ca 14000 (100 uVeff in gives 1.4 Veff out to phones).
Loading the cathode follower output with low ohm phones halves the output voltage (060725).
The receiver was now fully working in all modes on band 2 - 4 and ready for final alignment!! (060725).
7.2 Fine alignment of the oscillator frequency
The oscillator circuits were now aligned to very high frequency accuracy on band 2 - 4 in the same way as described above. Only a few minor adjustments of the inductance and capacitance values were needed, it could all be done with the ordinary alignment facilities. The accuracy was better than 5 kHz all over band 2 – 4!! (060710 – 25).
7.3 Fine alignment of the IF module and BFO
An alignment rig was built according to description in ref 1 (it is not possible to align the IF and BFO in the receiver). The alignment rig was working just fine! (061027).
The alignment was done according to ref 1 with topping of the input and output filters in the mixer and BFO. The 6 circuit filter could with a little experimenting be aligned to a good bandwidth and rather smooth curve using only a signal generator/counter and oscilloscope without a sweep generator. The crystal filters were in good trim and were not touched. A check of the IF curve was done in the receiver using the method described in 7.1. See the picture here. The IF curve
Bandwidth:
Wide +- 8 kHz +- 1 kHz at – 3 dB (specification +- 5 kHz)
Medium +- 5.8 kHz +- 0,8 kHz at – 3 dB
Narrow +- 500 Hz +- 100 Hz at – 3 dB (specification +- 200 Hz)
The curve is slanting a little to the minus side but the top is exactly at 1000 kHz and evenly high for all bandwidths. As the difference in height at the shoulders is less than 20% for all bandwidths it is acceptable. The curve is a little wider than specified, can be varied from 8 kHz down to 500 Hz, very good for DX-ing in AM, SSB and CW (061102).
The BFO frequency was aligned to zero beat in the manual control middle position , the frequency range was +-5 kHz. The crystal controlled tone is 1040 Hz. The manual control and around 3 kHz bandwitdth give a fair SSB reception (061103).
7.4 Fine alignment of the RF stages
I decided to postpone this until band 1 and 5 are restored.
7.5 Final test
The receiver was finally tested by listening on bands 2 - 4 with very good result! (061103-04).
I will now try to find missing components or substitutes and then restore band 1 and 5. I will also fine align the RF stages for all bands and make a final test of the sensitivity (preliminary checks have shown AM sensitivity of better than 5 uV). Until then the receiver will be used for extensive DX listening on band 2 - 4 which is 3 to 17,6 MHz.
The photo below shows the receiver at this time.
8. Restoration of band 1 and 5, completion of case and final test
Just before Christmas 2008 I was lucky to get all necessary coils for band 1 an 5 from a contact in Norway. After soldering them in place (not without some difficulty!), I could check and align all stages succesfully. I also made a screening plate over the oscillator/mixer module.
The case was now rubbed, cleaned and painted silver inside and with RAL7021 outside. A cover plate was made for the D/F connector. Two handles were bought, a bit sturdier than the original ones. They will be used to lift close to 45 kg! Signs with text for valve positions, antenna and phones input/output were computer generated and glued in place.
Now the receiver was connected to a signal generator, frequency counter, damping circuit, valve voltmeter and oscilloscope and a thorough final alignment and check of all stages was performed. First the oscillator was aligned for best possible accuracy at the scale end and middle points. After that the RF 1, RF 2 and mixer coils and trimmers were aligned at the end points of each band. As far as I could judge with my equipment the reciever now met the specifications. I now decided that the restoration had finally come to a happy end!
Because of the difficulties finding the missing coils the restoration had been delayd with two years until the summer 2009! Photos of the final restoration can be found in the photo gallery.
Links
Helge Fykse radio collecion with E52 Köln
Peter Gierlach DF3KT handbooks for restoration
Norsk Radiohistorisk Förening NRHF, spare valves
More on WWII receivers
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Updated October 27th 2009