fernandortp

30

hace 6 años

The second transistor is TS 2 and the previous one is TS 1 (converter). Between base and emitter of TS 2 it gives me on the mV scale, 0 mV (strictly 0.1 mV, but in the end it is at 0 mV).

Nico4706

3.081

hace 6 años

The resistors that polarize the base and the emitter of transistor TS2 must be checked. The collector has voltage, so that by applying a signal from that electrode, the signal is normal. The problem is when a signal is applied to the base or the emitter, the signal is weak or does not come out, because the transistor does not amplify, due to a lack of voltage between the base and the emitter. The voltage difference between base and emitter in a germanium transistor is of the order of approximately 0.2 V. Check the emitter resistance, R5, the base resistance R4, the secondary winding of the second FI, S20 and S21, measure bobi

Nico4706

3.081

hace 6 años

measure winding separately with respect to the midpoint, and winding from end to end. And for doubts the resistance R11. By the measurements it is deduced that neither collector current circulates, because it is practically the same as that of the funte.

fernandortp

30

hace 6 años

Measurements:
R4 = 151k ohms
R5 = 545 ohms
S20 with respect to midpoint = 6.5 ohms
S21 with respect to midpoint = 0.6 ohms
End to end winding = 7.1 ohms
R11 is part of a more complex component called a diode filter (DF), which includes 2 capacitors and 1 more resistor, so I will have to completely desolder it so that it can be medically separated.
I took advantage of measuring the C16

fernandortp

30

hace 6 años

which marks 16 microfarads, 10 volts and threw me 24.3 microfarads, so I replaced it with one of 15 microfarads but the problem persisted. I also checked that there is no continuity between the shield leg and the emitter or the base. I checked the voltages on the other transistors and their values are within what is stipulated in the scheme, as well as the voltage difference between the bases and their respective emitters. It will be relevant to check if it is the transistor, make a replacement and thus take advantage of measuring it?

Nico4706

3.081

hace 6 años

To measure the transistor you have to disconnect at least 2 legs. Some of the joints must be open. If the multimeter has a transistor meter it is much simpler.

Nico4706

3.081

hace 6 años

Capacitor C16 is to stabilize the base voltage of TS2. Many times it marks too much because precision is not taken into account, but you have to be careful, because when you mark more, it can be leaking. Therefore, the ESR or series resistance must also be measured in the electrolytic capacitor.

Nico4706

3.081

hace 6 años

The fourth leg of the trnasistor is connected to the shield and does not have to have connection with the other 3 legs, base, emitter or collector. It is connected to the positive

fernandortp

30

hace 6 años

Measurements in transistor TS2:
In the diode mode:
Between base and collector = 235 mV, negatively polarizing the base.
Between base and emitter = total continuity, negatively polarizing the base.
In hFE mode:
B = 0
Then I will try to get a replacement. Must it necessarily be the same code or can it be replaced by a different one?

Nico4706

3.081

hace 6 años

In the free market of Argentina it is achieved, but they do not ship abroad. If you know someone who travels to Argentina you can tell him to bring you. The one who has it is VUDUSA.

Nico4706

3.081

hace 6 años

https://articulo.mercadolibre.com.ar/MLA-659495141-transistor-germanio-af117-nuevos-_JM

Nico4706

3.081

hace 6 años

I had answered you, but without realizing it, I deleted the answer. The transistor to be replaced must be Germanium, PNP type, for RF radio frequency. For AF audio frequency does not work. It can be replaced by a silicon one, also for RF, but you have to change the polarization resistors, since the voltage between base and emitter is 0.6 V. You can search in a Philips or other brand radios circuit, which has transistors silicon, which works with 9 V. If it is 6 V, it will be more complicated, because you have to calculate the value of the resistances for that voltage.

fernandortp

30

hace 6 años

I really appreciate all your suggestions, Nico. I will go around to see if I find something similar, so I will consider this post solved once I install it and so I can attach a photo of this radio that represented a time in literacy by the Capuchin priests of the Mapuche-Huilliches Indians of the Osorno coast.

fernandortp

30

hace 6 años

A big hug

fernandortp

30

hace 6 años

I got an AF117 from a Tonomac radio. Measured in diode mode:
Base-Collector = 232 mV
Base- Emitter = 313 mV
B = 92
I don't know if that profit is good or if something is already exhausted.
I have put it on the radio and I had no major problems, it is heard quite well for the 2 local stations of my city, although for the Argentine stations that I usually listen to during the night, it is not very good, everything compared to another radio of the same model . The voltage between base and transmitter with the radio on is 289 mV. Attached some photos of this radio. How these radios brought

fernandortp

30

hace 6 años

I have removed the fixed variable capacitor on the board and moved it so that I can manipulate it from the outside, as seen in the photos. It takes some sockets for ground and antenna (it doesn't have a ferrite antenna), so if you don't connect a good cable as an antenna, it really doesn't get much. Something curious that happens to you, and that does not happen with the other similar radio, is that when you connect the ground, the volume drops.

Nico4706

3.081

hace 6 años

According to the datasheet, the DC gain (hfe) is 50, but that depends on the base current. For each base current there is a different hfe. Are the emitter, base and collector voltages indicated in the circuit?
In a town in Colombia, these types of radios were also used, and it was necessary to install an antenna that already came with the radio, to be able to capture the distant stations.

fernandortp

30

hace 6 años

Voltages measured with the radio without tuning:
Base = 0.78 V
Emitter = 0.49 V
Collector = 8.0 V
+ = 8.01 V
As I indicated, although the 2 stations of my city are well listened to, it lost selectivity to capture stations from outside. I have a good outdoor antenna and with that I can listen without problems on a similar radio to those other stations. In fact, before failing, he also had that ability and from one moment to another he lost power (and obviously selectivity). I've always wondered what this is about (selectivity). Of a good alignment ?, although at all I have manipulated it in

fernandortp

30

hace 6 años

that sense, not even in the intermediate frequency. I think these radios were first designed for Colombia, since they have that band selector that incorporated 3 more stations but in shortwave. Here in Chile for this region, the radio school program was broadcast only through the La Voz de la Costa station (900 kHz AM), so both the band selector and the tuner were blocked. Over time, the coastal people found a way to hack it and be able to tune in to other stations, but only AM, since for shortwave they lacked the corresponding crystals.

Nico4706

3.081

hace 6 años

When changing the IF transistor, a new adjustment must be made, or at least touch up the IF coil where the transistor is connected, since changing a transistor changes the setting. It is assumed that if no one touched the coils, what needs to be done is to retouch the coil where the transistor is connected, at maximum output, preferably tuning in to a station with little signal, to be able to make the adjustment with greater precision. In these radios, the frequencies are different from that of a common radio. The FI for example is 490 KHZ, against 468 KHZ of the common Philips radios.

fernandortp

30

hace 6 años

Adjusting the IF of the transistor in question there was no change, in fact the ferrite core remained in practically the same place for maximum output. I measured the voltages again, with the radio with and without tuning and with + = 7.93 V:
Radio without tuning:
Base = 0.69 V
Emitter = 0.42 V
Collector = 7.93 V
Tuned Radio:
Base = 0.79 V
Transmitter = 0.5 V
Collector = 7.93 V

fernandortp

30

hace 6 años

I did the same thing but with another radio of the same model that captures all the stations. Tensions with respect to + = 7.81 V.
Radio without tuning:
Base = 0.89 V
Emitter = 0.62V
Collector = 6.93 V
Tuned Radio:
Base = 0.51 V
Emitter = 0.25 V
Collector = 7.5 V

fernandortp

30

hace 6 años

So in a radio that works "well", apparently the tension in the collector never reaches that of +, whether tuned or not tuned.

fernandortp

30

hace 6 años

There would therefore be something that makes the tension in the collector the same as that of the source. You had previously mentioned that this fact would mean that no collector current would be circulating. Why does that happen?

Nico4706

3.081

hace 6 años

Did you measure the collector resistance R6, how much does it measure? because in the circuit it is not possible to see the value. Do the two radios have the same model? Are the resistance values the same? If there is 0 V there is no collector current, and therefore the hfe gain would be 0. The emitter voltages are more or less equal in the two radii, so the transistor is bad? and how does a hfe of 90? Look closely, some resistance must be altered. The collector current when circulating through the resistor R6 must produce a voltage drop over R6, and this voltage must be subtracted from the voltage d

Nico4706

3.081

hace 6 años

of the source, therefore, the collector voltage has to be less than that of the source. The voltages in the IF transistors are measured without a signal, because otherwise, the automatic sensitivity control CAS circuit acts on the basis of the transistor, reducing the gain. There are stations that have more power and others less power. What the CAS circuit does is level the amplitude of the stations, because a very strong signal can saturate the IF channel, causing distortion in the sound. In the case of PNP transistors, the CAS sends a + or - positive voltage according to the

Nico4706

3.081

hace 6 años

station power, and this modifies the gain of the transistor. In this radio the CAS is applied to the base of transistor TS2 through resistance R11 of 15 K. For a more accurate reading, you can measure the voltage directly on resistance R6, using an mV scale to know how much mark, some value different from 0. has to show

fernandortp

30

hace 6 años

I measured the resistance of collector R6 and it gave me amazingly 7.0 ohms, since according to the colors (gray-red-brown) they should be 820 ohms (something like that can also be read in the diagram), which I confirmed in the good radio , which measured 767 ohms (with the same colors). Tomorrow (today) I will completely desolder this resistance and verify this value again, and obviously to replace it, but that strange collector tension is already making more sense. I never thought that a resistance would lower its value, what I always heard is that at most they were cut (as infinite resistance).

fernandortp

30

hace 6 años

Regarding the spokes, the 2 are model B1X18T, the only thing that changes is the color, gray one (the first ones that were distributed), light blue the other, and the aggregate in the 3-coil rotor and their respective connections for the crystals. Of the latter I will also upload some photos.

fernandortp

30

hace 6 años

The soldered R6 of the plate measured about 760 ohms, so I had to track those 7.0 ohms that were still registered between their desoldered contacts. It turned out that the collector of the TS2 was short with the shield marking a resistance of 5.4 omhs, the difference with the total 7.0 ohms corresponds to the coils S23 and S22. Then I just proceeded to cut the armor leg. Now the radio is heard powerful from the beginning and with an excellent ability to tune.

fernandortp

30

hace 6 años

These are the voltages with the radio without tuning and without connecting the antenna (source voltage = 8.12 V):
Base = 0.75 V
Emitter = 0.45V
Collector = 7.3V
The model of this radio is B1X18T / 98. I leave some photos of another version that in the only thing that changes is in the color (light blue, green is really its degradation through the times) and in the addition of some coils for short wave, the crystals are not there and only their connectors I sincerely appreciate all the support Nico4706 offered me in this electronic adventure. Thank you.

fernandortp

30

hace 6 años

Too bad, I could not find the option to upload the photos. If anyone knows.

Nico4706

3.081

hace 6 años

It seems to me that in the comments you cannot upload images, only in the solution part, but only once, then only the comments part remains. It was better before, in which you could upload images in any response. But at least the problem was solved, although 2 TS2 transistors failed consecutively.

fernandortp

30

hace 6 años

Just to complement and delve a little into the failure of this type of transistors, I leave 2 sites that explain it:
https://www.vintage-radio.com/repair-restore-information/transistor_transistor-faults.html
https://www.radiomuseum.org/forum/af117_and_tin_whiskers.html#1,
where they point out that the AF117 are the least reliable transistors, since after about 25-30 years they begin to show signs of this failure (short internal circuit between their electrodes due to the growth of conductive hairs from the inner wall).