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My Beolab 5000

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Craig
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Craig posted on Thu, Oct 4 2018 8:37 PM

So beguiled by Peters Beolab that when I spotted this on ebay I had to enter into a two day long haggle with the vendor.....he was a hard man but we reached an accord and the deal was struck (not as good a deal as I was hoping, but a fair price judging by the quality of Peters machine).


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Craig
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I have identified a missing Bias on the first stage of the stereo decoder as shown below.....this will be my next task, I'm taking advice from solderon regarding this as I'm in the dark with tuners....I will continue to chronicle the exercise as iI go on....


Craig
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Made some measurements as attached...something is amiss around the muting, stereo level circuit,  Also when taking these measurements I had the set tuned to a station in the lower MHz area (around 93)....cant pick up much of anything higher up, the reception was still poor but  stable, as I connected the multimeter probe to the collector of BC113 (1) position 3 the hissing disappeared! checked around a few more places on the 20v rail and got the same result.....suspecting a grounding issue I realised I was still powering the set via my variac, disconnected it and powered direct from the mains and the hiss is now gone....a small step but still an improvement. Also when I depress the muting button on the front of the set I loose all output to the amp?


Beo_Jean
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Craig,

If I where you, I would replace those BC113 with BC550B.

Craig
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Craig replied on Thu, Apr 4 2019 8:13 AM

Charles

Would BC549BTA be an acceptable replacement.....it looks quite close to me?

Craig

Craig
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Following receipt of the AC187 and the replacement of the 1.6uf cap (111) and the reflowing of all the solder joints I've made, not too many actually, I now have a very respectable reception....due in part I'm thinking to fiddling around with the dipole antenna, so convinced am I that the antenna is the villain I have ordered a "all singing all dancing" FM antenna from amazon.....I'm also dipping in and out of stereo reception. This is to be expected now I have ordered replacement transistors! I'm not convinced I'm completely out of the woods.....Peter is calling round on Saturday to collect his Beolab 5000 and has kindly offered to loan me his Beomaster 5000 to enable me to make some comparison measurements. None the less I'm in a better place....and thanks to Solderon's encouragement I'm feeling good about the exercise once again.....


Beo_Jean
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Craig,

I think this BC549BTA ia a great alternative to the BC113.

Sorry for the late answer btw...

Charles

 

 

Craig:

Charles

Would BC549BTA be an acceptable replacement.....it looks quite close to me?

Craig

 

Craig
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Ok.....moving on, Peter called on Saturday and dropped off his Beomaster 5000 tuner to enable me to make some comparisons around voltage levels, I'm busy doing just that. I have to say Peters tuner is far more sensitive than mine and can pick up more stations. I have tuned both sets to the same channel and taken the measurements at the same time....I have scribbled them down and will tidy them up before posting tomorrow....


Craig
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Voltages measured so far...the voltages measured within Peters machine in parenthesis

 


Dillen
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Check the thin wires to the coils.

Martin

Craig
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Cheers Martin....thought you may be looking in from time to time ;¬)

Checked the thin wires in the front end coils and also checked them against peters unit and all are soundly connected, tuned both receiver's to the same channel again and had a probe around with my new scope.....it's going to take a little getting used too, lots of features that are a bit of a mystery to me right now.....however I connected both up to the scope from the test point at AF121/5 (69) the circuit above and got this trace, peters machine is the top trace...both machines sounded ok during the test.


Craig
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Craig replied on Tue, Apr 9 2019 9:12 PM

I also noticed during the above that my unit would briefly jump up in volume and clarity, the tuning meter cracks hard upscale....and then it all drops back down again?

Craig
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Ok.....following on from advice received from Solderon (Nick), and Martin I focused some more attention on the front end....I have discovered that when I touch one of the transistors inside the can with a screwdriver the tuning meter leaps up to a healthy level and the volume and clarity of the station I'm tuned to increase accordingly, its an appreciable increase in reception. I tried the same with Peters machine and there is no difference in the quality of reception or deflection of the tuning meter.....so I'm reasonably confident i'm onto something, my problem is identifying which of the three transistors it is...…...


Craig
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The red line identifies the tab in the middle of a coil that connects to the offending junction.....the circle in this pic shows the transistor itself, can anyone identify him and suggest an equivalent?…….I can always winkle it out anyway and maybe read any markings, but I would prefer to be sure, also when I touch this tab the low voltages I have been measuring around the muting and stereo pots increase significantly too.


Søren Mexico
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Opened one of mine, dont know if it can help

 


Collecting Vintage B&O is not a hobby, its a lifestyle.

Søren Mexico
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The drawing

 


Collecting Vintage B&O is not a hobby, its a lifestyle.

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