siemens: Identification of capacitors used in this radio

ID: 489475
? siemens: Identification of capacitors used in this radio 
06.Oct.18 19:21
34

Georges Van Campenhout † 28.4.22 (B)
Articles: 206
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der Forum members

Can anyone help me in the identification of this 2 capacitors? I found them in this radio.

What about their long term quality?

Best regards

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siemens: Identification of capacitors used in this radio 
07.Oct.18 01:03
34 from 974

Bernhard Nagel (D)
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Bernhard Nagel

These pictured capacitors are paper types with usually bad long term Stability. Small leakage currents in critical circuitry as the audio amplifier, especially when used as coupling capacitor to the power amplifier tube, will affect the correct grid bias voltage. There, they shall be replaced by plastic foil (Polypropylene) capacitos.

When used as a safety capacitor in the power transformer area, please replace only with certified types (275 VAC, UL/VDE/S/N etc. approved).

In the RF and IF part of the radio, I would not recommend to replace these paper capacitors as long as they have no defects like shorts.

And: please add the tube listing and pictures of back and inside views to the model page, thanks.

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siemens: Identification of capacitors used in this radio 
07.Oct.18 16:11
95 from 974

Georges Van Campenhout † 28.4.22 (B)
Articles: 206
Count of Thanks: 3

Thank you Bernhard for this info.

But my main question was to identify the maker of these resistors. The white one has in its logo  a double letter K, and the brown one an Omega, and the letters M anf f.

What does the letter b mean, on both models?

As requested I will upload pictures, as soon as the set is restored.

 

mfG

 

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Identification of capacitors KK and (b) 
08.Oct.18 00:10
137 from 974

Bernhard Nagel (D)
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Bernhard Nagel

After searching the RMorg forum the manufacturer for the KK branded capacitors can be identified as Kunkler Kondensator. They also have been produced in blue color to be seen e.g. in Grundig radios.

The Mf (?) logo in a circle or Omega sign is currently unknown for me.

The "b" printed in a circle or brackets denotes in my opinion a safety capacitor for permanent AC voltage load. I often found them in circuitry parts where the AC line voltage is RF blocked to the chassis, or AC/DC sets has these in series with antenna or earth connections. The "b" marked capacitors can be seen as the predecessor of the "Y" capacitors used these days.

In tube rectifier circuits these types were used from the plates to ground avoiding hum modulation on certain AM or short wave reception situations.

If these are old paper types, the important isolation properties are no longer present after decades ... For replacement in critical areas use only certified modern PP or ceramic capacitors for "Y" or "X" applications as noted in my first post.

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