nordmende: Globetrotter Amateur troubleshooting

Hello all!  I have a Globetrotter Amateur with a problem I can't track down. 

Radio works on all bands.  It is not working well on LW, but does seem to work. Alignment may improve that. 

On MW, it works just fine above about 780khz; below that it goes dead.  It is the Local Oscillator that quits.  

I touched a soldering iron to TR8, and it came to life, until the transistor cooled down.  I thought it was bad, but changing it did nothing.  I then found that I could do the same to TR9 and it would work.  I have also found that some resistance added to the base of either transistor makes it work okay, but has consequences on FM.

 

I have checked resistors and bridged capacitors in the oscillator section, checked for cold solder joints, etc, but haven't solved this.  

Anyone have an experience like this?

Thanks,

 

john 

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Hallo John,

 

long time ago I had a problem like this.

If I remember correct, please check up D249 (St-2,1-07/10S)

 

Greetings

Erwin

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Hello, Erwin.  Thank you for the reply; I think you may be correct!

 

I removed the diode and checked it; it does seem that one of the diodes is not conducting.  Trying the radio with the component removed, the oscillator does work all the way to 520khz, but there is much squealing like the BFO is turned on.  

What can I replace this with?  I have tried a couple of silicon diodes, also a couple of germanium diodes, but trying either kills the oscillator altogether.  I feel like I might need some series resistance with the diodes, but thought I'd ask you first. 

The part number (St-2,1-07/10S) doesn't show up for me in a Google search. 

regards,

John 

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Hello John,

 

I even don’t know how to get the St-2,1-07/10S and replace it.

But any replacement must produce exactly voltage, 2 Volts at all and 1.5 Volts at the upper diode.

The voltage at the St-2,1-07/10S does not allow tolerance.

I think, you can try a little LED may be red or yellow for the upper diode and a Si-diode 40xx or a Ge-Diode or a Schottky-diode for the lower diode.

 

Best wishes

 

Erwin

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Hi, Erwin.  Thanks for the info.  Unfortunately, I think I'll have to look elsewhere for the problem. I have been working with this all day and couldn't come up with a combination of diodes and resistors that would work. 

I pulled out an old Globetraveller III I have that works, and did some measuring.  D249 measured the same as the one in my Amateur. I put my old one back in and it is keeping the voltage at 1.5v and 2v respectively, as it should. 

With every step, I think I'm getting closer to the truth about this radio, but it is certainly a vexing problem!  Usually, the Globetravellers I have worked on were a simple fix, showing how well made they were.  

I'll keep looking.  Thanks for your help!

 

John 

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