Repair of speaker 75GDN-1-4. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Speakers
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The head of the loudspeaker of an electrodynamic type, low-frequency, round with an unshielded magnetic circuit 75GDN-1-4 (old name 30GD-2) is one of the most common and affordable for radio amateurs. It is intended for use in closed remote phase inverter systems of household radio equipment of the highest complexity group as a low-frequency link in enclosed spaces [1]. Recently, the demand for it does not fall due to the increased popularity of low-frequency speaker systems - subwoofers.
The 75GDN-1-4 head, like any other, has its drawbacks. It is known that in its design the weakest point is the contact lobe. Its base is made of cardboard, which is not able to provide sufficient rigidity. When installing the lead wires, it often bends and breaks - fig. 1. Because of what, the flexible wires going from the voice coil to the petal sag or, even worse, stretch. As a result, the probability of their breakage, skew of the mobile system increases. Which, in turn, entails touching the voice coil on the core and damaging it. And this probability increases with increasing amplitude of the diffuser oscillation.
a)
b)
Rice. 1. Dynamic heads 75GDN-1L-4 (a) and 75GDN-5-4 (b) with deformed contact petals.
It is quite obvious that a more rigid material should be chosen for the base of the contact petal, for example, fiberglass or getinax, as in some heads (not all) 8GD-1 (Fig. 2). Most hams cut the lobe out of a stiffer material. However, it is not so easy to transfer contacts riveted to a cardboard board. There is nowhere to find new ones. One solution is to reinforce the native board with a rigid plate.
Rice. 2. Contact lobe made of getinax head dynamic 8GD-1
The work is carried out as follows. Unsolder the lead wires of the voice coil from the contact lobe. The petal itself is unscrewed from the diffuser holder - fig. 3.
Rice. 3. Contact lobe of dynamic head 75GDN-1-4
From a fiberglass blank with a thickness of 1 mm and dimensions of 30 x 16 mm according to the drawing shown in fig. 4, a reinforcing plate is made. At the same time, the coincidence of the holes with the petal is controlled.
Rice. 4. Reinforcing plate
The plate is fixed with screws with a diameter of 2 mm from the lower side of the contact tab (Fig. 5, a.), threading the screws through the holes in the contacts with their heads facing them (Fig. 5, b).
a)
b)
Rice. 5. Contact petal reinforced with a fiberglass plate: a - lower part; b - upper part
If necessary, the plate is adjusted with a needle file, focusing on the contours of the cardboard petal. After that, the petal is installed on the diffuser holder and the lead-in leads are soldered. Threaded connections are coated with zapon varnish or nitro paint to prevent spontaneous unscrewing.
Such a refinement will allow you to safely mount wires of a larger cross section without fear of failure of the dynamic head.
The described technique is acceptable for repairing other heads of a similar design: 8GD-1, 30GD-1, 50GDN-3-4, 75GDN-1-8, 75GDN-3-4 (30GD-11), 75GDN-5, 75ZT-1- 4 (modern analogue of 75GDN-1-4).
The technical characteristics of the speakers, recommendations for use, repair, winding data of voice coils, etc. are indicated in the source [1]. Detailed tips for repairing loudspeakers are described in the source [2].
Literature
- Burko V. Household acoustic systems. Operation and repair - Minsk: "Belarus", 1996.
- Bolotnikov M. Loudspeakers - M: "Art", 1971.
Author: Vladimir Marchenko
See other articles Section Speakers.
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