telefunken: 7 Licensed by Armstrong; Opus :

Dear Members,

I have been working on the restoration of a Telefunken Opus 7.

Per schematics, screen voltage of EF89 in the last IF stage (tube4) should be 25V but I read 40V. All the components around EF89 are OK (C48,C47,W20,W21,C38 and grid resistor).

Anode voltage is around 220V which should be OK as well.

I swapped the EF89 with the one in previous IF stage (which shows the correct voltage values so I assume it is a good tube), still I read 40V. I have tried 3 different EF89s from other radios I have, the result is same.

Any thoughts about this issue?

Thanks in advance,

Cuneyt

 

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In the '50ies when the Telefunken Opus was produced, voltmeters usually had an internal resistance of 333Ω/V, and some had 1kΩ/V.  Today digital voltmeters read 10MΩ.

The voltages given in the schematic were measured with voltmeters of that time.

However, the internal resistance of a voltmeter loads the measured object. Therefore former low impedance voltmeters read lower values than modern digital voltmeters do.

Regards,

Dietmar

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