10th Apr 2019, 1:21 am | #1 |
Pentode
Join Date: Nov 2016
Location: Lisbon, Portugal
Posts: 187
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Metz 200k
Hello everyone.
It just came to my hands this set: Metz 200k, which I have never heard about. I search on the internet and I found no info about this set, nor the schematics It came with a non familiar (to me) valve set up: ech81, ebf89, ef86, el84 Since I have no schematics I check mains transformer (ok), rectifier bridge (ok), replaced electrolotics (50uf +50uf) and another electrolytic (4uf) that I believe is the cathode capacitor of the power valve el84. Also replaced all paper capacitors, and check majority or resistor when possible to assess the rated value. Problem: no sound in any bands, nor in p.u. Not even a spike of sound when touching el84 pins nor ef86 pins, nor output transformer inputs. High voltage present in two wires entering the output transformer. I am wondering if it could be a problem in the output transformer, but I don’t know how to test it. The loudspeaker is tested, and also the valves. Any help would be much appreciated. Thanks in advance. If anyone know a model set with similar schematics, please let me know. Cheers, Diniz, from Portugal |
10th Apr 2019, 8:48 am | #2 |
Pentode
Join Date: Oct 2011
Location: Oldham, Greater Manchester, UK.
Posts: 167
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Re: Metz 200k
Hi Diniz,
What is the voltage on EL84 anode(pin7)? if no voltage then check op transformer primary connections. If a voltage is present touching a capacitor say 0.01MF between anode and ground should produce noise spike in speaker. Frank C. |
10th Apr 2019, 9:25 am | #3 |
Nonode
Join Date: Oct 2017
Location: Bristol, UK.
Posts: 2,388
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Re: Metz 200k
Hello Diniz, how many wires are connected to the output transformer? There should be 2 to the loudspeaker (if you disconnect them and measure the winding resistance with a multimeter on the Ohms range it should read between 0.5 and 3 Ohms). As you say there are 2 wires with high voltage on them; if one is connected to the EL84 anode that tends to indicate the high voltage winding is OK, but to be sure disconnect the wires and measure the resistance of the winding, should be somewhere between 300 Ohms and 2000 Ohms. Sometimes there is a third winding in series with the primary high voltage winding as shown in the attached sketch. This winding is used as a choke for HT smoothing to reduce ripple and hum. If any of the windings is open circuit the radio will not work. If you are getting an HT supply to all of the valves then the output transformer will be OK. The other thing you can try is to trace the loudspeaker wiring because sometimes there is an extension speaker socket with switched contacts on the socket pins. These contacts sometimes stay open or get dirty which can open circuit the speaker connection. Good luck, Jerry
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10th Apr 2019, 9:39 am | #4 |
Banned
Join Date: Dec 2013
Location: Middlewich, Cheshire, UK. & Winter in the Philippines.
Posts: 3,897
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Re: Metz 200k
West German, valve line up is very common on UK and continental sets.
Metal rectifier? Try a 1.5v battery across the disconnected speaker in case it is seized. Then try it across the output transformer primary. |
10th Apr 2019, 9:53 am | #5 |
Rest in Peace
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
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Re: Metz 200k
Check any external/internal speaker switches if there is any.
Mike |
10th Apr 2019, 10:16 am | #6 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,536
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Re: Metz 200k
Might be an AM only version of this:
https://www.radiomuseum.org/r/metz_3093d.html Possibly an export model- data on those is notoriously thin on the ground. Cabinet looks like this: https://www.radiomuseum.org/r/metz_1211u.html Presumably this: https://en.todocoleccion.net/valve-r...joya~x28705905 is it? The valves are common in German sets, but usually as part of one of the multivalve "monsters" rather than a simple 4+R set.
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15th Apr 2019, 12:36 pm | #7 |
Pentode
Join Date: Nov 2016
Location: Lisbon, Portugal
Posts: 187
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Re: Metz 200k
I must apologize for the late reply.
I thank all comments and contributions. Frank C.: voltage on anode EL84 approximately 270 Vdc. No noise produced touching EL84 pins (we will see why later). Jerry: Thanks for the attached figure. The winding resistance of the loudspeaker was measured 6.8 Ohm. The resistance of the op transformer winding was measured 320 ohms. Boater Sam: yes, metal rectifier. Now the interesting part (shame on me ) When rechecking the voltages on EL84 pins I realized that no voltage was present in the cathode pin. The original burned EL 84 had been replaced for onother one of my collection... a tested valve (or so I assumed). It happened that, just to confirm, i replaced the valve for a second one from my collection... and the result was the set playing amanzingly!! A graet lesson for me.... I realy need to meke sure that i am using REALLY functioning valves. Although, i keep learning with you guys! Thanks once more, and apologies for the "newbiness" Cheers, Diniz from portugal! |
15th Apr 2019, 1:17 pm | #8 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,536
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Re: Metz 200k
It's a result, no worries. Do check the output valve grid coupling capacitor for leakiness unless it's obviously a plastic film or ceramic type.
(Measure output valve grid volts with high resistance DVM- should be within a few millivolts of the 0V line.)
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