ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Hi friends,
I'm working on an Amplifier 608 (blue faced version) which has so far been a both fun and challenging job. A well-built and heavy device that has obviously been a trailblazer back in june 1962 where this example was made (according to the stamp inside the cabinet - you gotta love those details), and in a nice cosmetic condition as well. Nothing not to like here except...it's not working.
By now the challenges and fun have slowly, but steadily grown into frustrations. I hope some of you may have encountered these problems before and may be able to share some advice as to what to look for?
The trouble is sensitivity. When connecting a source (tape level audio device AKA a smartphone) to tape or radio I will get an almost inaudible signal no matter which input is selected and with volume turned all the way up. When I connect the same source to the microphone input, I get a very loud, but also quite treble-heavy (no bass) sound when the sound level on the source is turned almost entirely down.
Add to that, the balance knob seems to work in reverse, meaning that turning it left mutes the right channel and opposite. And yes, I checked the speaker connections about 30 times over...
One of the ECL85s is crackling when touched, and I've tried switching it with one of the others, but to no avail. I also tried swapping the ECC83 with a new one I have, but no luck.
I should probably mention that I also recapped the whole thing as you can probably see from the picture.
I have downloaded the schematic from the vaults here at Beoworld and was hoping this would help set things right, but I'm a bit out of ideas now. So any help or suggestions would be much appreciated.
Crackling often suggests a bad contact in the valve socket.
Martin
Thanks, Martin. You were right, a cleaning of the contacts and some resoldering of suspiciously looking wires under the valve sockets eliminated the crackle.
Other things have happened since yesterday. For once, I discovered that I missed two small 1,6 uF electrolytics at the input selector module during the initial recapping, one of which was totally dead. Replacing with 2,2 uF (nearest value) made both channels sound alike and at balance (except with microphone input selected...), but it did not fix my overall sensitivity issues. So, I went looking for other suspicious things, and I discovered that somebody in the past had been messing around with wires behind the input DIN sockets. The grey wires on the images below are probably not original. One is connected to a red/white original wire, the other to a purple/white original. The red/white is connected to a pin on the radio input DIN, the other was not connected to anything - just lying around behind other wires. I have no clue what this is supposed to do, perhaps a bypassing of some sort, but I really have no idea.
So my question goes: Are any of you able to help me with an image of the original wiring including the correct wire colors?
Please see the images below.
Just a quick update. Giving attention to the inputs, I found out that the previous owners' messing around with the input wiring is quite extensive. Not possessing the best schematic reading skills in the World, I nonetheless managed to get the microphone input to work through which I can now play music - and that means actual pleasantly sounding music! Tape and radio inputs still don't work though, but I will look into this one input at a time. In the mean time, if someone out there has a detailed photo of the wiring to the DIN input sockets including wire colors, it would be very much appreciated.
One week and quite a bit of progress later, the 608 now works perfectly on phono, microphone and radio (to which most modern devices can be connected). I had to rewire the radio input as it was totally messed up. I've also checked all the inputs as specified in the schematic, and it seems B&O wired the tape input to work as a recording output as well, making it different from the other inputs. Still not sure that the tape input is wired correctly, but I can live with that - at least until I see an example of original wiring to check if I made any mistakes.
A good hint seems to look for solering points that are not looking 'old' or original - if they're too shiny or bubbly or just don't look like most soldering points in your piece, somebody has probably been 'working' on them, and they may very well have been doing something wrong...so start by checking up on the suspiciously looking soldering points!
Also, the pilot lamp wasn't working due to a broken wire inside the bulb itself, but I found a replacement in my boxes of parts soldered out of scrapped electronics.
The cabinet also needed a bit of restoration to the veneer including a few replacement pieces, a thorough cleaning and polishing.
So, for now, I'll enjoy the 608 and the lovely, really pleasant and natural sound from it!