Question about Siemens H-42

[John-Jarratt]

I want to adjust the I.F. transformers on this Siemans H-42. Do I need a special tool to adjust the cores? They seem to be glued with a black substance and do not appear to have a groove in them to rotate. Any advice would be appreciated. Thanks

[holger66]

Hi John,

these horizontal cores are suitable for AM, they normally need no realignment. (The vertical cores are for FM.) If it is nevertheless necessary, you will have a major problem. The cores have no screw threads, they are fixed in straws with the glue, that you see. To loose it, you have to heat it up carefully, the core will get moveble then. The procedure is described in the Siemens alignment instructions for these radios sets.

I never did this in reality and would not risk it. Sorry....

Holger

[John-Jarratt]

Thanks Holger: It's good to know what lies ahead if I decide to adjust cores. I find this radio insensitive to distant AM radio stations even with a good external antenna. But it receives local broadcasts well. FM is very good. Here in Canada almost all AM stations are DX. We have only one local station where I live. This is the first example of this model I have seen so I am not sure if I am expecting too much for AM performance.

[holger66]

John, due to the fact, that this set has no AM pre-stage, AM performance is on an average level only.

Following my own experiences the sets made by Loewe-Opta in Düsseldorf (model names starting with "Rhein-": Rheingold, Rheinperle...) have the best AM performance of all german sets made in the 50´s, when it comes to sensitivity.

Best wishes
Holger

[John-Jarratt]

Yes, I have to agree that Loewe Opta made very good radios. I have a small Bella Luxus and a Meteor model. They sound very good on FM. Saba and Telefunken probably had the most consistantly good radios throughout their product lines. Generally speaking, German radios made in the 1950's were among the best of that era. My issue with this H-42 though, is that it is only receiving my one local AM station and cannot hear anything else ,even at night. I used my signal generator to confirm that it does process the signal throughout the AM band. The external antenna does not improve anything but does make the local station stronger.

[holger66]

I am sure, you have renewed or at least checked the ECH81. Is the voltage at the anode of its triode ok ?

H.

[John-Jarratt]

Yes, I have checked the voltages at the ECH81 and they are within normal range. I have tried another tube. All resistors are OK. I have been checking the components along the path of the antenna signal from the antenna to the first grid of the ECH81. There is continuity but I can't seem to find one adjustable coil. It is the one that the arrow points to in the attached photo. This coil is a common path for the AM bands. Do you know where it might be? I realize there were different production runs of this radio and perhaps my radio does not have it. If you look at the Richtantenne in the schematic you can see a coil which connects directly to the ECH81. My radio does not have it because it was made at a point in the production run where this coil had not appeared or was removed for technical reasons.

[Radiowerkstatt]

Hello John., Holger 66

You have a late<r> Model.
They have a positive Feedback from Grid2 ECH to Ferit-Antenna, to improve the Sensitivity on Ferrit-Antenna see 2pictures "Coil" and "Circuit".

Johann

Pic. coil from RMorg.

[glaubnix]

Hello John,
the marked from you resonant circuit is the intermediate frequency rejection circuit. It should also be present in your device.
It is within the key set and is denoted by "16". In the following picture it is marked.

H42-Sperrkreis.JPG

It does not affect the reception sensitivity.

[John-Jarratt]

Thank you Radiowerkstatt and Glaubnix. You information is all I need to look at this circuit more intensively.