Advantages of tube radios_Tube radios modified into tube amplifiers

Advantages of tube radios

Compared with semiconductor radios, the biggest advantage of tube radios is that the sound quality is obviously better than that of semiconductor radios! The second is that they are stable and generous, and at the same time have the temperament of classical beauty! In addition, the history of tube radios is much longer than that of semiconductor radios, so they have certain advantages over semiconductor radios in terms of collection!

Tube radio modified tube amplifier

I bought two old tube radios of the same model from the second-hand electronics market at a very low price (15 yuan each). After inspection, one power transformer and two output transformers are good, and the two 6P1 tubes can also work normally. The power transformer is a 50WP product with the model number DB-50-300 from the 27th factory of Shangwu. The quality of the transformers of Shangwu factory is unquestionable, and the technical indicators leave room for improvement. If appropriate measures are taken in the circuit, a power transformer can be used for long-term dual-channel operation without damage.

The output transformer is the CB-2-75 model of the factory. The output power is 2W. Although the output transformer does not adopt the modern layered and segmented special winding process, it still sounds good.

Because the sound quality of the original voltage amplifier tube 6N2 is not satisfactory, the author uses Beijing brand 16N3J electron tube for voltage amplification. This tube has good high and low frequency sound and the sound is charming. In order to further improve the sound quality, the power amplifier tube 6P1 adopts triode connection method, and the grid negative voltage can be appropriately increased, that is, the cathode resistance value is increased from the original 300Ω3W to 400Ω4W (using 2 220Ω2W resistors in series). This not only improves the power tube drive voltage amplitude and efficiency, but also reduces the power tube working current. A 50W power transformer and a 624 rectifier tube can be used for long-term dual-channel work without being too worried, killing two birds with one stone.

This machine has only 2 coupling capacitors for dual channels. Different brands will have different sound performance. High-quality products should be used as much as possible. The filter capacitor uses the domestic capacitor of Qiji "Tianhe" brand, and the pre-stage filter coupling uses CBB film capacitors. The sound is beautiful. The cathode bypass capacitor uses the Japanese ELNA Jinzi audio special electrolytic capacitor.

The choke can be replaced by a 220V 10W high-quality tortoise-source transformer. Note that the iron core should be changed to a one-way plug-in method.

Since the output power of this amplifier is relatively small, a paper cone full-range speaker unit with a sensitivity of 4Ω is selected for playback, which has a good sense of hearing and musical expression.

Lifespan of a tube radio

The design life of electron tubes is generally around 2000 hours (special tubes have 5000 to 10000 hours), but in reality many electron tubes are no longer broken after 2000 hours (generally speaking broken means: no sound is produced), it just means that its performance does not meet the design standards. By the time the tube actually stops producing sound, it may have reached 3000 hours or more; the actual service life of the pre-stage amplifier tube is even longer.

If you use it for 5 hours a day, you can change the tube once a year; but this is only the tube you can change to achieve practical design performance, and the replaced tube can still be used for a long time. To give the simplest example: an old cathode ray tube (cathode ray tube is also a kind of electron tube) TV, the actual service life is more than 10 years!