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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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8th Feb 2018, 12:54 am | #1 |
Pentode
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Grundig 97A problem FM
Hello everyone,
I am working on this set (grundig 97A). The set performs well on AM, but no signal on FM. No voltage on ECC85 anodes. Please see attached image to understand my explanation. When the set come to my hands, point A was connected to point C (is this open circuit from A to B, A conneted to C). R27 mesured: 1.1kohm I rewired according to the diagram and voltage mesurements across R27 as printed in the image. One side of R27 starts with 90V and keeps incresing and the resistor warm a lot and starts smoking. Still no voltage present on the anodes of ECC85. Suggestion/comments will be helpful and welcome. If anyone can in addition explain me the meaning of C43 symbol I would appreciate. (I just print part of the diagram not to violate the forum rules). Thanks in advance, Diniz from PORTUGAL |
8th Feb 2018, 2:24 am | #2 |
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Re: Grundig 97A problem FM
You have a short that is pulling the voltage off R27. I cannot find C43 on the diagram.
I suspect that A and B should not be connected to the chassis ground, C is ground. Why did you change the wiring from what the set had been working on? |
8th Feb 2018, 9:44 am | #3 |
Rest in Peace
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Re: Grundig 97A problem FM
The circuit should be wired exactly as shown in the diagram. Points A, B. & C are the HT supply to the ECC85. No part of this line shouild be earthed (grounded) At first I suspected that C42 was leaky or even short-circuit. I cannot find C43 on that diagram, either.
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8th Feb 2018, 10:26 am | #4 |
Pentode
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Re: Grundig 97A problem FM
Thank you BoaterSam and Livewire for your comments.
Boater Sam, I changed the wiring because it was not working on FM, and R27 was smoking. So I rewired as presented in the diagram. When the set came to my hands, the "ground" end of C42 was connected to R27 and not to ground. R27 was not connected to point B either. Livewire, I'll make some measurements and let you know the performance of C42. Thanks in advance. |
8th Feb 2018, 10:29 am | #5 |
Pentode
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Re: Grundig 97A problem FM
C43, see attached.
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8th Feb 2018, 10:36 am | #6 |
Dekatron
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Re: Grundig 97A problem FM
The two capacitors highlighted in the photo are feed through types, the wire going into the body is the same as the wire that comes out of the body, eg: it's a straight through connection that internally connects to one plate of the capacitor, the outer of the capacitors body that's soldered to the chassis is "ground" and it's connected to the other plate of the capacitor, C43 on the receivers schematic decouples the heater supply to the ECC85.
EDIT: Post crossed. Lawrence. Last edited by ms660; 8th Feb 2018 at 10:46 am. |
8th Feb 2018, 10:45 am | #7 | |
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Re: Grundig 97A problem FM
Quote:
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8th Feb 2018, 10:55 am | #8 |
Dekatron
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Re: Grundig 97A problem FM
I've since edited my last post which might explain things a bit better but if not have a look at this:
http://navyaviation.tpub.com/14030/c...ilters-222.htm The left hand diagram is the feedthrough type and the shaded horizontal bit is the feed through wire. Lawrence. |
8th Feb 2018, 1:06 pm | #9 | |
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Re: Grundig 97A problem FM
Thanks for the link
Quote:
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8th Feb 2018, 1:15 pm | #10 | |
Pentode
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Re: Grundig 97A problem FM
Quote:
C42, was indeed shor-circuited!! Replaced by a normal capacitor (two end capacitor) and FM is back!!!! Since C42 is a feed through type, as Lawrence mentioned, is this replacement ok? I just connect one end to R27 and the other end to the ground/chassis... Thanks so much. (image of C42 attached) Diniz |
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8th Feb 2018, 1:39 pm | #11 |
Octode
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Re: Grundig 97A problem FM
I had to replace one of these with a standard capacitor on my Grundig 97A, it must be a common fault.
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Stephen _________"It`s only an old telly" ___ |
8th Feb 2018, 2:12 pm | #12 |
Pentode
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Re: Grundig 97A problem FM
I'll follow your experience and keep my replacement.
Thanks. |
21st Feb 2018, 4:07 pm | #13 |
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Re: Grundig 97A problem FM
Hi,
I invite you to see the final result of the restoration. https://www.youtube.com/watch?v=Yt4A...ature=youtu.be Cheers and thanks for your help. Diniz, PORTUGAL |
13th Mar 2018, 6:08 pm | #14 |
Pentode
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Re: Grundig 97A problem FM
Hello again,
Something went wrong with the set. I believe that my father didnt assemble the set properly. Since the loudspeaker is not the original one, I believe that a short circuit was made (somehow) between the loudspeaker chassis and the base of EM84. That resulted on a mains transformer damage Anyone can tell me the outputs of the mains transformer? Iis it PRI:220 -->SEC:180 + 6.3? Thanks in advance, (poor grundig 97a ) |
13th Mar 2018, 9:16 pm | #15 | |
Dekatron
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Re: Grundig 97A problem FM
Quote:
I would say the secondary HT winding should be higher than 180 volts, I would guess around 205/210 volts based on the HT voltages given in the schematic and the fact that the receiver is fitted with a selenium bridge rectifier, the current rating would be at least 75mA. 6.3 volts is correct for the heater winding, the current rating would be at least 2.7 amps. Lawrence. Last edited by ms660; 13th Mar 2018 at 9:30 pm. Reason: change voltage |
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