Vintage Products

Re: Beogram 42VF - some questions

Dillen — Sun, 06 Nov 2011 02:29:21 GMT

All original pickup cartridges bear the B&O logo. And that goes for the inner (coil) part as
well as the outer (needle) part.
No B&O logo = not original.
There were countless manufacturers of more or less suitable cartridges and needles,
some could be combined with B&O parts, others not.
Some were surprisingly good, others eh.. not quite so good.

Martin

Re: Beogram 42VF - some questions

ablaumeise — Sat, 05 Nov 2011 18:32:59 GMT

Just curious: What exactly is the difference between these two? The 75µ came with the Beogram, so I suppose this is the orignal. Unfortunately the stylus didn't survive shipping, so now I'm using the 15µ.

Re: Beogram 42VF - some questions

Dillen — Sat, 27 Aug 2011 01:11:31 GMT

Good job !

Repairs to faults that has no "natural" cause are often the worst and most time consuming.
Particularly if you are not aware that somebody has modified something so you are merely
checking what would normally go wrong.

Martin

Re: Beogram 42VF - some questions

Søren Mexico — Fri, 26 Aug 2011 23:43:11 GMT

No need to be ashamed, you fond the failure and thats it, I've done a lot of works where I looked for failures for days, and not finding them, stopped took a long brake, and went back to the basics.

Re: Beogram 42VF - some questions

ablaumeise — Fri, 26 Aug 2011 13:39:44 GMT

You know how sometimes you spend an eternity looking for a problem, and then suddenly you stop and think: "Wait, have I checked...? I mean it's obvious, I'm sure I have...right?". Well, then you know how I feel right now.

I was measuring the supply voltage to the amps. You know, the voltage behind the power supply section. The voltmeter showed -50V. That can't be right. I mean, the minus. So I stopped and considered "in relation to what?". Well, I had it connected to the black cable of the AC supply. Which, according to the diagram, should be connected to common ground. However, there was no voltage at all in relation to the chassis. So I checked the preamp board. No connectivity between the AC input and ground. And that's when it dawned on me. The connection was not on the board, but between the connectors. Remember - those connectors that somebody had messed up to bypass the preamp? Sure enough, there was no connection. That's when I started to feel like an idiot. So I soldered a piece of wire on there, connected the turntable to the amp, set down the needle...music. Not sure if I should feel happy or ashamed.

Re: Beogram 42VF - some questions

ablaumeise — Thu, 25 Aug 2011 10:51:29 GMT

When the base is grounded, it oscillates between 1,7V and no connectivity. Excuse my ignorance, I was born long after the days of germanium semiconductors.

There are 25V after the diode, I haven't measured further down the line yet.

Just bypassed the preamp, and yes, it works fine. Just a bit too quiet, if you know what I mean.

Strange. I checked the connectors, the caps, the transistors, the diodes, visually checked for bad solder joints...and yet this thing is dead as a doornail.

I'll have another look at it tomorrow, I've used up my patience for today.

Re: Beogram 42VF - some questions

hemenex — Thu, 25 Aug 2011 09:58:37 GMT

ablaumeise:
they also measure 1,7V e->c

Did you leave the base floating? 0.1V are easily catched when left open and then they trigger the transistor - even with the voltmeter only.

(Was learning by doing for myself too - my germanium days are way back now... Anyone remembers the black OC something's?)

Ground the base while measuring & check again.

Are the 20 volts ok? I found the diagram for a BG1000 with a little different schematic: From 14VAC they create 33.5V DC after the 2 diodes, 28.5V at the first cap and 16V at the 2nd cap. But there are different transistors, both already silicium. EDIT: oops, I meant silicon

P.S. did it work without the preamp, using the short circuit plate? (yet another EDIT: just read there never was a short circuit plate - should say "did it work while bypassed"...)

Re: Beogram 42VF - some questions

ablaumeise — Thu, 25 Aug 2011 09:38:07 GMT

Thanks for your input!

Replaced the diodes with 1N4001s - still nothing. Checked the capacitors - capacitance and ESR both measure out fine.

Checked the transistors out of circuit - they also measure 1,7V e->c...they shouldn't do that, should they?

Re: Beogram 42VF - some questions

tournedos — Thu, 25 Aug 2011 07:57:58 GMT

The diodes seem just rectifiers for the power supply, I'm sure 1N400x:s or similar silicon diodes will do.

I think it was the AF11x types that are most likely to grow internal whiskers... but all germanium transistors are rather fragile by today's standards. Anyway if they work, I'd leave them alone; the exact measurements can vary a lot.

Re: Beogram 42VF - some questions

hemenex — Thu, 25 Aug 2011 07:57:17 GMT

ablaumeise:
the breakdown voltages measure about 0,15V on both transistors

I have some AC151r's that should be a replacement for both the AC126 and the AC107 (as far as I can read beaker's schematic)

They have 180mV measured on B-C and B-E so the 0.15V aren't too bad.

And looking at the supply it shouldn't be a big deal using 1N400x or even 1N4148's as there are 12.5Volts AC so .4V difference won't lower them too much. And the OA85 had 50mA only... but change both diodes anyway.

As far as I can see this is a voltage doubler circuit - I would expect some 20 Volts supply after the different RC-stages.

Probably the bipolar electrolytics?

hx (still lovin' his BL4500's )

Re: Beogram 42VF - some questions

ablaumeise — Thu, 25 Aug 2011 07:32:52 GMT

Does anyone have a good quality scan of the preamp-schematics? I can't really read most of the things on beaker's scan.

What I've found so far: AC126...wasn't it those that grow crystals or something?...both test ok, but the breakdown voltages measure about 0,15V on both transistors, whereas on the other two (2Nsomethings) it's the usual Germanium 0,3V. Also, one of the two diodes is open circuit. Can I replace this with a standard 1N4001 or is a Ge-Diode required?

Re: Beogram 42VF - some questions

ablaumeise — Thu, 25 Aug 2011 05:26:11 GMT

Thanks to Martin, there finally is some progress:

For future reference: The bearing on the ST/L and the Beogram 1000 tonearm is identical, the arm itselft is not (the ST/L arm is longer due to the different counterweight). So...bearing replaced, adjusted - speed is perfect, tracking weight is perfect, arm perfectly adjusted...put a LP on there, take the cover off of the SP7, lower the cueing lever - I can hear the faint sound of Fehlfarben's "Hier und Jetzt" emitting from the stylus, turn up the receiver...

Guess what...I've found the reason why the preamp was disconnected. It produces nothing but a faint hum. Let's see what we can do about that...

Re: Beogram 42VF - some questions

ablaumeise — Sun, 24 Jul 2011 07:21:00 GMT

Thanks! I now reassembled everything the way it should be.

Well...so close, and yet something rather important is still missing.

Re: Beogram 42VF - some questions

beaker — Sun, 17 Jul 2011 05:05:44 GMT

Here you go. Anything else you need, just let me know.

Re: Beogram 42VF - some questions

ablaumeise — Fri, 15 Jul 2011 10:58:17 GMT

Well…that was a bad idea. Just started working on the BG again, finally got the matching paint and repainted the baseplate. Problem: Turns out if you travel the world for two months and come back you might not remember what goes where. And I didn't take pictures. Ha.

Umm…Beaker? Or somebody else who owns a 42? Could you please take a picture of the innards? Just with the bottom plate off. I have no idea as to how to route the cables or where exactly the voltage selector was located before...