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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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27th May 2011, 5:40 pm | #1 |
Pentode
Join Date: Mar 2007
Location: Kayseri, Turkey.
Posts: 124
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rectifier and transformator replacement
dear Friends,I have a germany radio, telefunken gavotte9.there is no power transformator inside,and there is a rectifier( AEG B250 C75 N2) but the rectifier is faulty.I have some questions;
-I have a another transformator,the transformator have two 380VAC secondery.can I replacement this transformator? -I have a another rectifier,SEMİKRON C1500 L 5 B. can I replacement this rectifier? -last ,there is a 0.15 mikro farad capacitor.for you,must I replacement with 0.1 mikrofarad or 0.22mikrofarad cap? |
27th May 2011, 8:12 pm | #2 |
Pentode
Join Date: Mar 2007
Location: Kayseri, Turkey.
Posts: 124
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Re: rectifier and transformator replacement
sorry,transformer secondery is two 350VAC.and rectifier picture.
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27th May 2011, 9:02 pm | #3 |
Rest in Peace
Join Date: Mar 2006
Location: N.W. Oxfordshire(Chipping Norton)
Posts: 7,306
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Re: rectifier and transformator replacement
The Transformer with two 350VAC secondaries is too high in voltage for the Gavotte.
You need one with secondary 250VAC at most, plus a low voltage secondary of 6.3VAC at about 2.5 to 3 Amps for the valve heaters and dial lamp(s). If possible, get a circuit diagram of the radio first. This should list the voltages and currents needed. That rectifier may be suitable, but, what I have done in similar cases is to use four 1N4007 diodes, putting a 100 to 150 ohm resistor in series, to replace a faulty selenium rectifier such as the B250C75N2. As to the 0.15uf capacitor, I would use an 0.22uf. The voltage rating should be equal to, or greater than, that of the original. If this is wired across the mains, then a class 'X' capacitor should be used in it's place |
28th May 2011, 4:00 pm | #4 |
Pentode
Join Date: Mar 2007
Location: Kayseri, Turkey.
Posts: 124
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Re: rectifier and transformator replacement
I didn't understand that; where will I put a resistor, to after bridge rectifier.between bridge rectifier and smoothing capacitor? and I found a new rectifier but there is no information on that.only there is 7C5 mark, that picture is now.for me 250VAC and 75miliamper,is it O.K.
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28th May 2011, 6:52 pm | #5 |
Rest in Peace
Join Date: Mar 2006
Location: N.W. Oxfordshire(Chipping Norton)
Posts: 7,306
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Re: rectifier and transformator replacement
I definitely WOULD NOT use that rectifier in your post#4-it is another selenium type, which
may be unused, but is probably 40 or more years old, and could fail soon after fitting. The 100 to 150 ohm resistor in series with modern silicon rectifiers, such as the 1N4007, can be wired between the transformer secondary and the rectifier, or between the D.C. output of the new rectifier and the rest of the circuit. I fit this resistor on the input(AC)side of the rectifier |
28th May 2011, 7:15 pm | #6 |
Pentode
Join Date: Mar 2007
Location: Kayseri, Turkey.
Posts: 124
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Re: rectifier and transformator replacement
it is O.K.sorry but I am a amateur.
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28th May 2011, 7:41 pm | #7 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,536
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Re: rectifier and transformator replacement
The sketch is correct for the resistor between the transformer and the rectifier.
The other position suggested would place the resistor between the +ve output from the rectifier and the +ve terminal of the capacitor. Either position is OK. The resistor simply modifies the forward resistance of the silicon rectifier so that it is similar to the forward resistance of the original selenium unit. This keeps the HT voltage closer to its design value than the higher voltage you would get with just a simple replacement of selenium by silicon.
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