April 23, 2022 at 3:43 pm #4407
Thought I would check the fuses out too before powering up…..this is what I found.April 23, 2022 at 4:11 pm #4409
Removed the link and cleaned up the fuseholder…new fuses installed. Gingerly applied power from the variac up to 220v……and nothing happened, not necessarily a bad thing…there was no smoke or sudden popping of new fuses…..so a little fault finding exercise required….as for now a glass of wine is called forApril 23, 2022 at 4:40 pm #4410mexkingBRONZE Member
- Mexico city
Keep them coming, I like your work, think about chancing the Fairchild (black drop) transistors, Frede, Classic Audio recommend changing them
April 24, 2022 at 8:08 am #4421
- This reply was modified 1 year, 7 months ago by mexking.
This is true Soren….I received this from Frede some time ago:
It is actually a ”short list” 😊
BC 550B for npn
BC560B for pnp
When the Beolab was designed (before 1967) only a few transistors were available is really low noise versions – therefore B&O have chosen a number of different types of coarse also being able to be used and meeting the actual voltage level. But I have for many years used the above type in the pre-amplifiers.
And I am using the transistors type B because higher gain in classic electronics design is not a good idea (this is my opinion 😊)
B U T — for the power amplifier and the power supply – I only use the original RCA types !!!
For the output power transistors and psu transistors — I am only using the original Motorola or RCA (there are to many “fake” 2N3055 out there).
When I am writing the original it is actually the original because I re-use these transistors from Beolab 5000 which is scrapped.April 24, 2022 at 10:25 am #4423
Started by checking the 240v supply to the transformer…..all good, 32v output to the new rectifier and around 40vdc out of the rectifier. Checked the 20vdc supply and found it was around 29vdc…adjusted the new trimmer I installed and brought it back to 20vdc……checked the voltage to the power ON lamp and that was good too…..so replaced the lamp and of course it illuminated ;¬)
Connected a antenna and adjusted the tuning dial, the stereo lamp flickered as it passed through live broadcasts which was very encouraging…..however the tuning meter stayed hard down throughout.
April 24, 2022 at 10:30 am #4425
- This reply was modified 1 year, 7 months ago by hcraig244.
Thinking I may have damaged it during cleaning I took it out, looked ok and when I put my multimeter across it to check the moving coil continuity the needle deflected 3/4 up scale, as you would expect from the current from the meter set to ohms. I got out a meter I recently replaced due to severe clouding of the lens to compare….and found this curious thing……April 24, 2022 at 10:38 am #4426
The polarity of the meters are opposite, someone has erased the + / – markings from the left hand side meter and marked them up opposite to what they where…….the right hand side meter is the one with the milky lens and still has the + / – markings unchanged,
The negative marking can be seen against the right side post, the meters have different shapes too….change in design down the years I expect.April 24, 2022 at 10:47 am #4428
However I extended the + wire and soldered the cloudy meter in place and ran another test, all worked fineApril 24, 2022 at 10:52 am #4429
Deciding the way forward was to replace the cloudy lens with the not so cloudy lens on the one I had just installed I set about dismantling the not so cloudy meter and discovered the internal connection from the + post was loose….tightened it up put it back together and having removed the newly extended + wire I soldered it back in place…..and yes everything worked fine!……spent a couple of hours on thisApril 25, 2022 at 5:25 pm #4447
Completed all the component replacements….including the “fairchild black blobs”, fitted BC550B’s.April 25, 2022 at 5:29 pm #4448
Hooked up to a Beolab 5000 and an antenna, and I have to say that in spite of the occasional unexpected minor issue this tuner sounds tremendous….crystal clear and very stable….all that remains is to put it all back together ;¬)April 26, 2022 at 10:44 am #4462
Made a start on the front panel and curser…..takes quite a bit of fiddling around to get the felt pads back in along with the nylon studs on which the curser rides…..April 27, 2022 at 10:09 am #4503
All complete and fully tested…..does sound very good for an old girl, I think it can now be identified as restored……
- You must be logged in to reply to this topic.