[R-390] OT: Need advice regarding Blaupunkt tube radio

[george stringe]

Barry, this has the sound of a broken wire in the antenna input 
circuit.  I don't have schematic avail but the symptoms are that the 
antenna signal is feeding in via a small capacitance (not capacitor) 
hence the lower frequency am and sw are weak and the higher frequency fm 
signal will feed in better via random capacitance in the antenna input 
circuit.

george
WGØS


On 1/2/2011 3:26 PM, Barry wrote:
> Hi Ross,
>
> I did remove the cover from the first IF transformer, mainly because the lower ferrite core was difficult to turn.  Thinking it was made more like some of the transformers I've worked on (e.g. R39i0A), I thought I might be just twisting the insides; however, once I removed the can, it was apparent that wasn't the case.  These are made quire well and I wasn't twisting the windings after all.
>
> If I'm not mistaken, the caps are not the "sandwich" type like I've seen before, but they are very small diameter, quite long tubular caps that run vertically inside two of the corners.  I don't know if these are as prone to the silver disease as the sandwich styles.
>
> The B+ is indeed off and I assume I do need to replace the main filter caps.  There's slight hum on the output, but I don't hear it at low levels so the AC on the B+ isn't very bad.
>
> Hmmm, still not sure where to go from here.  There are some other electrolytics that I figure should be replaced; however, other than that, shotgunning the caps doesn't seem to be a need here.  This model used very high quality components, at least for the day.
>
> Thanks again,
>
> Barry - N4BUQ
>
>
>   On Sun 02/01/11  3:26 PM , bavarianradio at comcast.net sent:
>> Hi Barry, I have restored many Blaupunkt tube sets. The most common failure
>> in these is the 460 kHz transformers. I have rebuilt many of them. Try
>> tapping one while feeding your 460 kHz generator into the ECH81 grid and
>> see if they act intermittently. Even though you seem to be getting a peak,
>> there could still be a problem. Rebuilding the transformers requires
>> removal from the chassis or circuit board, removing the aluminium can,
>> removing the "sandwich" type mica capacitors and installing new silver
>> micas on the bottom, 150pf for the input and 250pf for the output.
>> Otherwise, have you recapped the entire radio yet?? also check for proper
>> B+ voltage as well.  Good Luck, Ross
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