DG’s Practical Notes, Geloso G110, 1952-1956

Aug 8, 2021 09:10 · 1642 words · 8 minute read

Vintage radios and alike have lethal voltage, so only personnel with the proper training should make or attempt such repairs.

00:12 - If you elect to follow any of the practices and procedures described here, you are doing so at your own risk and under your full responsibility.

00:21 - If you do not know what you are doing, do not attempt any of the following practices and procedures.

00:43 - The front knobs are removed. The screws are covered by an insulating plaster, because, when turned on, the radio chassis is connected to the main power grid, and touching it by chance could be lethal, even through the hidden screws in the knobs.

01:01 - Therefore, in this case, removing the knobs requires some effort.

01:15 - Once the front knobs are successfully removed, the rear cover is opened.

01:27 - The white screws are not the original ones: they have been replaced with nylon screws, to avoid getting in contact with the internal chassis, while operating the radio.

01:40 - On the rear radio cover there is an extra knob and a small switch: they are not part of the original device and they will be removed during the restoration.

01:50 - The original radio configuration allowed to select the grid voltage, but in this case it was modified to a fixed 220 Volts, to avoid dangerous mistakes; therefore the selection jumper is also missing.

02:04 - During the restoration this safety measure will be kept.

02:11 - Before extracting the chassis, there is still a knob to remove, the one on the side, used to select the wave band.

02:23 - An additional circuit was added to this radio, a B. F. O. (or Beat Frequency Oscillator), with the purpose of listening to S. S. B. (Single Sideband) communications.

02:36 - All the extra components are removed, starting from the additional potentiometer and switch.

02:45 - The main B. F. O. circuit was shielded inside a small tin box and powered by the line used for the light of the dial.

02:52 - Therefore, the corresponding light bulb socket is missing.

03:01 - The chassis is finally extracted. Before proceeding any further, the vacuum tubes should be removed and put in a safe place.

03:47 - Each one is packed separately and the name is written outside.

04:29 - The case is separated completely and then dismantled.

05:08 - It will be cleaned and recomposed later. Before removing the connection with the B. F. O. circuit, it might be useful to understand how it was actually connected.

05:37 - The sealed tin-case must be opened. The circuit appears to be a variant of a project published on an old Italian Electronic magazine, with the addition of a voltage regulator and of a double varicap diode to tune to the IF frequency.

07:40 - To apply the B. F. O. signal, the radio was modified, as highlighted in red in the schematic.

10:49 - The B. F. O. is finally removed and the original radio circuitry is restored, although only temporarily in this phase of the restoration.

11:05 - The orange electric wire that was connected to the B. F. O. circuit, was the source for the 6 Volts A. C. , originally meant for the dial light.

11:18 - That wire, like the others coming from the transformer, was insulated with rubber, which now has become rigid and is broken in many places.

11:33 - Therefore, all the transformer wires should be checked carefully and then replaced or insulated properly.

11:42 - Usually, factory radio schematics are drawn with the purpose of having them compact, often making them difficult to interpret.

11:52 - It is also necessary to consider that the official schematic might be slightly different from the reality of radio under restoration.

12:00 - Before proceeding any further, it would be important to prepare a radio schematic that one could understand easily with confidence, following the personal inclination regarding the way that such schematic should actually be drawn.

12:14 - Numbering the components is also very important.

12:21 - It would be also the case to prepare a practical schematic of what is actually under the chassis, because the actual position of some components could make the difference.

12:34 - This process is an investment for any operation that would follow, especially if it is necessary to dismantle and then remount the radio.

12:47 - The labels appearing in various parts of the radio, including the components, contain important information regarding the story of that particular device and of the components.

12:59 - Before cleaning and before replacing components, it would be appropriate to prepare some replica labels, which at least resemble the originals.

13:09 - Those labels could be used later, and also some new capacitors could gain the original look.

13:16 - Having a copy of those labels and making sure that they will accompany the radio is important, regardless of the policy that will be chosen in current restoration style: some other person, in the future, might decide to give the radio a more historically-consistent look.

13:36 - This radio is very compact and it is very difficult to reach the components that are located in the lower levels.

13:45 - It is taken the decision to dismantle everything, so that also the chassis could be cleaned and properly protected from rust. Only the RF and the IF modules will remain internally untouched.

13:58 - To remove the power transformer and the IF transformers, a more powerful soldering iron is necessary.

14:36 - It is important to remember that generally the IF transformers are different, so, before removing them, it is necessary to do something to distinguish them later.

15:26 - After failing the attempt of cleaning thoroughly the chassis with the tube sockets still on it, they are also removed carefully.

15:50 - Before reinstalling, the components should be checked and prepared.

15:58 - The capacitors that are in good condition, seem to have kept reasonable insulation, so they will be reinstalled.

16:08 - The problem of this compact radio is the insulation between the components: before reinstalling, they will be prepared to avoid unwanted contacts.

16:21 - In particular, the small mica capacitors have lost the external coating and some heat shrink pipe is used to provide better insulation. However, it turned out later that shrink pipes are stronger than the capacitors, which might bend (and break).

17:01 - The power transformer requires particular care, especially considering that it could be hardly replaced.

17:10 - The original transformer’s wires are losing their insulation completely. In fact, around 40 years before, some wires of the transformer were already replaced or better insulated.

17:25 - However, insulating the wires is not sufficient and later also some hot glue is used to make sure that no short circuit would be possible.

17:54 - The tube sockets are installed using regular small screws and nuts, but the screws are inserted inside-out, so that nothing would protrude inside the chassis.

18:16 - Then the chassis ground line should be connected carefully, so that these connections would remain at the lower level, near the internal chassis surface.

18:54 - The next step is the heaters (or filaments), and from now on, everything should be carefully insulated.

19:10 - Even the terminals of the tube sockets should be insulated, because the space separating them from the chassis is extremely small.

20:16 - Then the IF and power transformers are installed and progressively connected, always with care for the insulation.

20:39 - Also a fuse holder is installed in a place that seems to be safe; however, later it will have to be moved from that place.

20:55 - The radio is prepared for a connection that would include the external ground connected to the chassis, for the occasion in which the radio is tested after an insulation transformer.

21:17 - After completing the connection of the power transformer, it is appropriate to verify the voltages provided, before installing more components on top.

21:28 - The values read with the multimeter are higher than specified in the original schematic, but at the moment there is no load at all and a significant drop is expected after the radio is completely rebuilt.

21:45 - To connect the loudspeaker a small tripolar socket and plug is added, for practical reasons.

21:59 - The chassis is slowly repopulated with all its components.

22:14 - The vacuum tubes are mounted too and the voltages provided by the power transformer are tested again: now they conform to the expected values.

22:28 - Luckily, no mistake has been made in remounting the chassis: it is already working, although it requires some tuning.

23:29 - The next step is the dial and its tuning cord.

23:35 - It is important to verify that the movement of the dial index is conforming to what is printed on the dial.

23:47 - The power transformer is supposed to provide an output of 6 Volts for the dial light, but the real voltage oscillates between 8 and 12 Volts.

23:58 - Instead of a regular filament light bulb, a 12 Volts LED light bulb is added, after verifying that it works correctly with that voltage fluctuation.

24:12 - Everything is now prepared for mounting the chassis inside the radio case.

24:22 - In particular, the external ground is no longer connected to the chassis ground.

24:35 - In the radio case, the loudspeaker is separated by a thin iron net, which already has some rust stains.

24:44 - A piece of clothes is added for aesthetic reasons.

24:52 - Finally the chassis is mounted in the radio case, but it is necessary to add extra insulation, to avoid the possibility of touching the chassis inadvertently, while operating the radio. .