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

[Barry]

Hi Ross,

I'll give that a try.  I disconnected the filter caps and jumpered in some good ones and I think the voltage did rise just a tad, but not much.  I don't remember exactly what I was getting before, but I'm now running about 25V low (214 instead of 240).  I checked the transformer output and it's good so it must be the selenium rectifier.  I know they're bad about burning out in a smelly way, but I did not realize they get "resistive" over time.

Apparently the small rise in voltage really helped the FM.  It is a lotclearer than it was last night.  It really sounds good now.  I need to align it, but in the meantime, at least it is working nicely.

Yes, it is the 460kc transformer I disassembled.  See it at:

http://n4buq.shutterfly.com/pictures

As a side note, there are two small spring clips that hold the internal assembly together.  Last night, I was reassembling the first clip and it went "p-ting!" as it flew across the table, ricocheted off the face of the signal generator, and then flew across the shop.  I looked for it for about 1/2 hour last night and gave up.  Today, I pulled almost everything off the floor on the side of the shop where I last heard a "tink" and finally found it.  At least the shop got a good cleaning...

Thanks again,
Barry - N4BUQ



 On Sun 02/01/11  8:24 PM , bavarianradio at comcast.net sent:
> Hi Barry, The reason the B+ is low is not because of the filter caps,
> although you should replace them, You need to replace the selenium bridge
> rectifier with a silicon bridge and a 100 ohm 10 watt resistor(in series
> with the+ lead)  Be sure that you disassembled one of the 460 cans and not
> one of the 10.7 mHz cans.  You really should replace ALL of the paper caps
> as well. Although Blaupunkt used better papers than Grundig and Telefunken,
> they do still fail unexpectedly. Also, replace the small electrolytics  as
> well, pay particular attention to polarity as one of the electrolytics has
> + connected to ground. (agc stabilizer) Keep us posted!! Ross----- "Barry" n4buq at knolo
> gy.net> wrote:
> Hi Ross,
> I did remove the cover from the first IF transformer, mainly because
> thelower 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
> seenbefore, 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
> 
> 
>