Bodensee 3DS

      Hello Achim,

      Thank you for the quick replay. Yes all the paper caps were replaced as the power elko also. All the tubes were checked/replaced with my funke19.
      The sound is not a hum, it is a mechanical sound originated on the vibrating axis motor when it remain in stand by position. The motor was polished and oiled however it remain noisy. I have others Freiburg from 6 to 15M without that ugly sound.
      Thank you again, Bruno.

      Hello Bruno,

      did you also replace the two 50µF electrolytics for the negartive voltages in the power supply section?

      The motor, as you probably know, is kept vibrating by design to reduce it´s friction. So it can start rotating gently when the automatic finetuning comes into play (because the oscillator is drifting for example).

      This vibration can be felt when you touch the tuning dial but it shoudn´t be heard distinctly of course.

      Here´s how the 50 Hz "vibrating voltage" is fed into the motor control circuit:



      The 15V~ voltage from the power transformer´s (b)-terminal gets to the gate of the ECL80´s triode.
      To check if this 50 Hz signal is causing the vibrations you could disconnect the 50nF capacitor (or the 2M resistor) and observe if the vibration is still too strong.

      Sidenote: You can see in the diagram how vibration is reduced when you switch to shortwave by adding the 6 MOhms resistor when K3 is open. Normal vibrating would rhythmically detune shortwave stations.
      Achim

      Hello Achim,
      Yes, the two small 50 uf Elko were replaced for security. All the resistors involved in the negative voltage supply has normal values. The actual negative voltages were reported on the post 059 and ALL they are three time over the values according the schematics. I don´t know if I should change the 2K resistor or if those voltages can be tolerated.
      Thank you for your interesting technical details. I will report your suggestions after work.
      Bruno.

      Hello Achim,
      I have checked all your red path in my set. The 2M & 6M resistor are ok, the 50nf paper cap was replaced and the voltages on ECL80 pin2 are - 8.8 with K3 on and - 7.7 v with K3 open.
      After the 2M resistor was disconnected there was NO change at all in the motor axis vibrations.
      Now the motor noise is puzzling me !!

      Gruß, Bruno.

      Hello Bruno,

      first there´s no automatic stop at the ends of the scale in the 3DS models. (This feature was introduced in later models.)

      As for the noisy motor - what happens when you disconnect the control circuit and leave only the AC supply voltage connected?



      Since you said you already replaced all the paper capacitors I assume you also replaced the two motor-capacitors (0,5µF and 0,3µF).
      Achim

      Hello Achim,

      Thank you so much for your information and invested time. Unfortunately after the two motor wires were unconnected the motor shows not function at all. If only the ECL80 anode wire is disconnected the motor does not work also.

      All the paper caps and elko around the motor tuning unit (EABC80 & ECL80) have been replaced and all the resistor remain inside normal tolerance values. Both tubes are TFK NOS.

      The only detected abnormality is the higher negative voltajes reported on post 059.

      I don't know if the EABC80 variable cathode resistors can have some importance....

      Thanks again for your help,
      Bruno.

      Hello Bruno,

      the motor will not work without the control voltage and only 300V~ power connected - this is o.k..
      I assume ist was silent in this state?

      If so, we should focus on the ECL 80 tube "Rö 10". Maybe the bias is wrong and the 50Hz vibration-signal is amplified more than it should be.
      Can you measure the plate current of the pentode system?
      It must be 18 mA when the automatic is inactive.
      And you should also measure the current at the screen grid. It must be 2.5mA.
      Achim

      Hello Achim,
      I apologize for not replay yesterday.
      When I have disconnected the two motor wires (control voltage), the motor remain dead and NOT as in standby function. The 270 AC voltage from c & d points have no effect over the motor with the control voltage disconnected. The motor remain silent for sure.

      Today I have measured the ECL80 current plate: it was 23 mA with inactive automatic.
      Unfortunately the pin 6 remain in a extremely tight space and the screen grid was impossible to access.

      have a nice day, Bruno.