BOSCH 360 (Late), Help me
BOSCH 360 (Late), Help me
Who can help me?
I have one radio Bosch 360W with the problem doesn't oscillate in any wave. He had several problems, among the ones which, without audio already resolved. Now I need to solve this, or be. The circuit oscillation doesn't work. This radio have the resistance (R15), tension division, one of the which, I designated it the 2.ª ( see fig.1), it is interrupted.
Please, anybody know how to inform which the value of the resistance? It is that in it part catalogue, only have the reference and in the designation "multiple resistance”. The resistance that is interrupted it the one that will give tensions to the grill of the 1.ª and 2.ª tube’s. Already changed the same ones, 56 and 58. I already tried to put several resistances, of values between 200k ohms and 750k ohms, but without result.
(Fig.1)
.jpg)
See schematic complet
(Fig.2)
forumdata/users/3656/BOSCH_360W_usa.jpg
Thank's for your's help's
Best Regard's
Júlio Branco
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- BOSCH_360W_cut_usa. (44 KB)
- BOSCH_360W_cut_usa. (44 KB)
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Dear Julio: the key here is R1. Through R1 you have the following: the plate current of the first two 58 + the plate current of the 56 + the screen grid for the three 58s. That's got to be no more than 30 mA and no less than 20mA. So knowing how much R1 is in value, you can calculate the voltage drop, which will give you the working point of the first two 58s. So the schematic says 240V on plate of the 2A5 but only 220 on the 58s, which means you are dropping 20 Volts. So R1 must be between 700 and 1000 omhs. Please measure R1 and, if found between those values, then we know I am correct.
Now AFTER R1 you are left with a small current, perhaps 10mA, to feed the rest of the circuit, which is the two 58 screens. Now these are operated at a much lower voltage, 100V, and then we are are left with only the screen of the first 58 which is about 50V. So a 100V drop with a 10mA current is 100.000 ohms...
Try resistors between 82K and 100k (2W) and see if it works. You can even go as low as 47K. Can't hurt. Hope it helps
Mario
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BOSCH 360 (Late), Help me
Caro amigo Mario,
Gracias pela tuya pronta respuesta.
En primero quiero té decir la R1 tiene 1000 ohms la R3 = 8kohms e la R4= 7kohms.
Yo estoy hacendó las experiencias que usted hay me propuesto.
La primera experiencia que hay hecho con una resistencia de R2= 47 k ohms. Se verificó que la tensión tiene 40 voltios para la segunda “58” (grid) con una entrada de 200 voltios. La R3 para la primera “58” (grid), tiene 20 voltios. Se verificó que lo radio hacia uno ruido muy alto que más parecía radio frecuencias misturadas con audio frecuencias. E este ruido solamente hacia entre la gama de frecuencias de 800 kHz hasta 1600 Khz, sintonizando lo radio
De seguida voy hacer las experiencias siguientes, en breve te digo.
Espero que entiendas este mío español, pero que yo no escribo muy bien. Mas entiendo perfectamente lo idioma español.
Hasta la próxima, muy brevemente.
Julio Branco
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Hola Julio: el ruido es porque la radio no esta oscilando, entonces lo que escuchas es la RF amplificada pero no hay mezcla. Las tensiones que da la tabla son estas:
válvula etapa plate screen grid
58 1st. detectora 220 40
58 1ra IF 220 95
58 2da IF 240 95
56 oscilador 75 -
Yo creo que algo esta mal ahi con estos voltajes. Para la placa de la osciladora la tensión sale despues de R1 pero hay otra resistencia (R16) que deberia ser de 25k, mira si esa resistencia esta buena y luego mide la tensión de placa de la válvula 56, a ver que pasa. Saludos cordiales
Mario
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Languages
Dear Julio and Mario
Well done, you have posted correctly from the model and later somebody with the same model will immediately see that. You started in English to get a bigger community here and selected also the flag for English (language choice within the editor). Well done too, but then you changed into Spanish for your answer.
Please only change into an other language if it can not be avoided.
If you feel that you get good answers in Spanish right away then use Spanish (with the flag for Spanish) - if you don't get your answers you might open up the same in an other language with that selection.
Here t might be good to translate this to Spanish and to begin again (same way) - preferably you change your statements here to English too. Sorry to bother you.
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Hello Julio: The noise you hear mixed with audiofrequency is probably due to the fact that the set is not oscilating. So what you hear is amplified RF but there is no mix wth a local signal and therefore, no IF produced. As per the table, the voltages should be as follows:
Tube stage plate screen grid
58 1st. detectora 220 40
58 1ra IF 220 95
58 2da IF 240 95
56 oscilador 75 -
Something is wrong with the voltages you have in your set. The oscilator plate gets connected right after R1 but then you have another resistor in series (R16) which should be 25k, check if that resistor is good and then measure the plate voltage in the 56 tube and see what you find
Kind regards
Mario
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In English
Ok Dear Ernst, here it goes told in English my first experience that Mario proposed me, I'm sorry.
Dear Mario,
Thank you peel yours prompt answer.
Beford more, i want to find out that the resistor R1 there is 1000 ohms the R3 = 8kohms and the R4 = 7kohms.
I am have one experiences that you me proposed.
The first experience that there i fact with to resistance of R2 = 47 k ohms. It was verified that the tension has 40 volts for second o'clock" 58" (grid) with an entrance of 200 volts. The R3 for the first one" 58" (grid), it has 20 volts. It was verified that I radio it toward one very high noise that seemed it lives I radiofrequencies it mixes with audio frequencies. And this noise only toward among the range of frequencies of 800 kHz up to 1600 KHz, syntonizing the I radio you
Of followed I go to make the following experiences, shortly I tell you.
Until the next one, very shortly.
Best Regard's
Júlio Branco
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BOSCH 360 (Late), Help me
Dear Mario
I’m sorry for only now giving the results to you of this repairing of the Bosch, therefore, as it is habit to say itself "gave water for the beard". It was a very difficult repairing, the radio very was moved, in my opinion, for curious, inclusively I arrived at the conclusion that the transforming one of entrance, (high tension), already was not of original, therefore he was me to debit it raised tensions, the IF completely were misadjusted and reel oscillator's, etc., etc. Then we go to the results that I got later conclusions that I arrived and as your aid. Before still to continue I want to inform you that the Bosch already is to work perfectly, are these challenges that more enthusiasm, makes to remember me constant challenges that had when worked in Informatics during 30 years, and when it is obtained to reach the objectives the one that in we consider them, happyer we are. However well, as the transforming one was not original and was to debit a raised tension, almost 350 volts, placed a reeled resistance of 1,1 k ohms/10W in series with reels of magnetic field of the speaker, then I started to have the 220 volts in the plate of 1.ª detector (58) and the same tension for the first IF. And, to obtain the correct tensions in screens grid and plate of the oscillator (56) The our "R1" had that to be of 16Kohms to obtain the tensions with correct values in screens grid in 1.ª detector, 1.ª IF and 2.ªIF 40 and 95 respectively; and to obtain to have in plate of the (56) 75 volts I had that to modify the R16 of 25Kohms for 20Kohms. It was then with the correct tensions, but the radio did not catch nothing in no band. I stopped the repairing I made a pause of one or two days, and came back "to the load", started for measuring you reel them of RF entrance and to follow this circuit all if it existed incorrect linking’s, as well as all you reel them of the oscillator, everything was well until for curiosity I measured the C40 condenser, of 0.06mF apparently was good, (it did not have ticket), however substitutes it for another of one approximate value, because in Portugal if it does not obtain to acquire with this value, sadly, I placed the one with approach value of 47nF. Turn on the radio, it is not that it starts to oscillate and to catch emitting national everything it are of frequency and with many interferences.... Now only it remained to adjust me IF 456KC to adjust to all the condensers, of them you reel oscillators and trimmer’s in accord with the dial, and the radio was operational, with a good profit quality of sound after substituting some condensers that were "dry", others with escape, and already I gave for finished the repairing, places it together with the others.
Thank you, one more time for your contribution
cordial:
Júlio Branco
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Congrats again
Mario
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BOSCH 360 (Late),
Profound compliments to both Gentlements
Senor Julio Branco you are displayin persistence with patience
Best regards
Jose Duarte
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