Vintage Products

Re: B&O Amplifier 608

berggren — Mon, 16 Aug 2010 11:56:16 GMT

Now that I have the schematic - thanks Peter ! - I will try to preserve the unit in pristine condition. It´s tempting though to bypass the two switches at the output and wire permanently for 4 ohms (windings in parallel as per Quad). I was wrong about the low voltage. General Electric´s Tube Manual ("Essential Characteristics") indicates 170 Plate/Anode volts at 41 mA (Class A) for the 6GV8/ECL 85. The actual supply is 300 Volts. B & O says each pentode should be set at 20 mA. Measuring the output transformers I get some 170 ohms between pins 1 and 3 and 195-200 ohms between pins 3 and 6. So one should target a drop of around 3,5 V and 4 Volts respectively between these points when setting the bias. Does everyone agree ? Best regards LB

Re: B&O Amplifier 608

Peter — Wed, 11 Aug 2010 10:37:30 GMT

They are sitting on my desktop waiting for you! email me at peter (at) beoworld.org

Re: B&O Amplifier 608

Peter — Wed, 11 Aug 2010 10:34:53 GMT

Thought I had! Did you send me your email?

Re: B&O Amplifier 608

berggren — Wed, 11 Aug 2010 04:51:07 GMT

No, I never received a schematic. There are a lot of aging capacitors, especially in the preamp. One wouldn´t like to work on it without a schematic. Also, the S/N ratio wasn´t to great even when new. Someone on the net successfully revised the ground connections (on another B&O model, but still) which makes it even more difficult if one should try it blindly. For instance, Rogers Cadet is fitted with ECL 86´s and has a fine reputation. Best regards

Re: B&O Amplifier 608

Dillen — Thu, 05 Aug 2010 16:02:21 GMT

Didn't Peter send you the schematics ?
I remember scanning it and he replied to your (first) post.
http://forum.beoworld.org/forums/p/29509/233473.aspx#233473

Parting out a 608 amplifier would be a shame in my opinion and drastically modifying it would reduce
its selling value considerably.
It's a quite well respected amplifier and a collectors piece. Not too plentyful either.
About 500-1000 euros seems to be the going rate, depending on condition. The last one I
noticed brought EUR 1300 on Ebay, but the transformers may of course be worth more to you
or maybe you don't care about the selling value and just want to experiment with the parts.

They are well built amplifiers, what's wrong with yours ?

Martin

B&O Amplifier 608

berggren — Thu, 05 Aug 2010 14:05:24 GMT

Since I haven´t been able to obtain a schematic I´m thinking of dismantling my 608 for parts i.e. the transformers. It´s based on four ECL 85`s probably chosen to allow a lower voltage but they are rare nowadays. I suppose one could rebuild it using EL 86´s and a suitable phase splitter which would make up a small power amp. There is a separate winding to supply the preamp and fixed bias. Perhaps this could be connected in series with the HT supply to increase the voltage and allow for more common ECL 86´s. The fixed bias could easily be drawn from the HT supply. Any thoughts on this ?

Best regards Lars Berggren