Pig in a poke

ID: 183054
Pig in a poke 
06.Feb.09 18:30
0

Lars-G. Lundelin (FIN)
Articles: 143
Count of Thanks: 3

Hi radio friends
Whenever you buy an old radio on an Internet auction, you'll buy a pig in a poke. If you are lucky enough the radio will be untouched, doesn't matter whether working or not.
If the set is not working, you can go on without a schemtics, but if it's been tampered with and the guy before you hasn't been skilful enough, it can be a real challenge to get it work without instructions.
This article is not meant as educational stuff but only as a warning and of course not related to any specific brand or make but my latest refurbished object, the CENTRUM HW5, may now stay as a typical example.
After the compulsory preliminary visual inspection of the circuitry, I noticed bad soldered tags and tubes that had been mixed up (in this model, there is only ONE possibility to put in the tubes in a wrong way. Talk about Murphy's....).
The electro-magnetic loudspeaker connections were so messed up that I supposed it was already gone but fortunately not.
The real problem with set was the heavy sharp humming, sounded like my old chainsaw. After replacing most of the capacitors (the set is from 1933), I connected the mains and heard even a more sharper "chainsaw" sound.
With my old Oscilloscope (a TRIO CS-1577) I watched a heavy rippled waving voltage from the B-terminal. Checked the groundings of the scope probe but the picture still waving. WHAT on the Earth could it be......I thought I'd checked all the lines and points...but then, when I measured the mid-tapping of the secondary of the transformer to ground, I got a reading of 68 ohms. I followed the lead from the mid-tapping down in under the chassis to the end of a heavy duty wire wounded resistor which was grounded. Yes... this lead was connected to the wrong end of the resistor. I think the resistor has something to do with the biasing..
The set is now working perfectly with a lovely clear sound. 
This was the third time now I was confronted with these kind of problems and the future seems not to be better when I'm glancing at the Saba 446WLK, presently upside down on my workbench.
 Anyway, this is the challenge which is making this hobby so interesting. I know people sitting for hours and doing crossword puzzle.
 

With regards

Lars-G.


 

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 2
Auction Sites 
09.Feb.09 01:17

Mark Andrews (GB)
Articles: 88
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Mark Andrews

I agree with Lars on this. When buying of auction sites, you never know what you might end up with. I think it pays to study any photos and descriptions carefully and ask for more photos if not too sure. I narrowly avoiding buying a fake Emerson once. It was when I studied extra photos it became apparent that something was not correct.  Another 'mistake' I made was on a small 1930's radio. There was no model or description and the photos looked like it had been tampered with but when it arrived, the only thing that was untouched was the case! The chassis had been cut in half and other bits added. I took the approach that the set would never be hugely valuable and there was not enough of it left to restore so decided to 'manufacture' a new/old set in the original case and chassis. It worked out OK but it could never be listed here due to the lack of information. Having said that it was a challenge as Lars would agree and this is why this is a long standing hobby of mine.

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 3
Caveat emptor!... 
09.Feb.09 02:10

Todd Stackhouse (USA)
Articles: 151
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...the Latin phrase 'caveat emptor' ('Let the buyer beware') has never been more appropriate than now thanks to the popularity of buying and selling things online.  I guess I can consider myself fairly lucky that I haven't had any real bad experiences so far with on-line buying...most of the sellers are reasonably honest and up-front, but there will always be those few who don't really know what they are talking about at best, and are outright dishonest at worst...

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 4
More caveats 
09.Feb.09 07:00

Michele Denber (USA)
Articles: 129
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Michele Denber

That's certainly good advice.  I would add that it is good practice to remind the seller to pack the item very carefully.  I have had two radios arrive with cracks in the case, damaged in transit.  Another one arrived with a tube rattling around loose inside.  I always insist on insurance too.

Some radios require special precautrions, like the German DKE-38, where it is very easy to accidentally snap off the power switch that sticks out through the back of the case.

 

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 5
still more caveats 
09.Feb.09 11:42

Konrad Birkner † 12.08.2014 (D)
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Konrad Birkner † 12.08.2014

It is a good plan to remove the speaker from a Bakelite case for transport. Screw it to a board and the cone it safe. And if the packet is dropped, the shock willnot break the speaker loose from the cabinet.

I also recommend to remove a glass scale from the set, wrap it in thin paper and stick it to a wooden board with adhesive tape.

Bubble wrap (large bubbles, ca 20 mm) 2 layers, made by using 3 stripes, one each around every plane.

Double boxing is good, and reinforced walls using 4-6 mm plywood or hard paper can avoid damage from outside. All that will add volume and weight, but it is worthwhile. I never had any complaint.  Such is my experience from more than 100 radios I had mailed across the pond.
In contrary there had been some insufficient packed radios I received damaged up to basked cases.

 

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 6
And let's not forget protecting the tubes!... 
10.Feb.09 07:10

Todd Stackhouse (USA)
Articles: 151
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...also, the tubes/valves should be removed and individually packed separately when packing up a radio for shipment, especially if they are rare or otherwise difficult-to-replace types...having a tube rattling around loose inside a radio when it arrives is certainly disconcerting, but that rattling could well have also damaged the tube...

 

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