I have a request...
Could one of you take a picture of each original external cap so I can print the original label on a sticker I will put on my grey cans.
Thanks in advance
Cedus: do you use 240V AC in your country? If so, you may be able to rewire your power transformer from 120 to 240V. Check your serial number. Units # 6606 and up have split transformer primaries and can be converted to 240V.
The mistake regards this part of the schematic :
And more especially the 1M and the 12K resistor you see in the schematic. How it is wired in all the 8Bs I saw pictures of. Even mine was wired like that :
To summarize on this picture :
Pin A is linked to : Pin 7 of the 6CG7, 12K resistor,
Pin B is linked to : the 0.1uF and 0.33uF cap through the white wire, 12K resistor, 1M resistor
Pin C is linked to : Pin 2 of the 6CG7, 1M resistor
Ok now let's compare this to the upper shematic. Obviously there is a problem.
The 1M resistor should be in fact between the Pin A and Pin C otherwise this is not at all the schematic but something else.
When I found that I went to check in all the photo I had and everywhere (this should more than 6 original 8Bs it was wired like that !!! I scratched my head for tens of minutes trying to find if I missed a wire or something but after checking and rechecking I could not find any solution. And the light came the solution was to find a VAC Marantz 8B reissue to see how it was wired and I had one in stock :
And... what do we see... the 1M is wired correctly between pin A and C.
So what's wrong have the original 8Bs got a wiring mistake nobody never saw except the people in VAC.
I have no explanation for the moment and I would like to have your opinion on the matter... please...
I hope this did not disturb too much your christmas time. I found that today and I do not know what to think !!!
Hey Steve that's one heckuva post! :thmbsp:
I suspected this had to do with the special compensated feedback network used in the 8B.
I believe some manufacturers of the golden years actually introduced small errors in their schematics to disuade others from replicating their circuits. This could well be the case with the Marantz.
I do know they were quite secretive about certain proprietary circuits. The 10B tuner for instance. They didn't publish an schematic until late 1965. No service manual was ever available for it.
I have the original service manual for the 8B, published by Marantz in the late 1960s (Woodside NY address). It has very little information about the feedback network. There are no instructions on how to adjust feedback for best bandwidth and minimal parasitic oscillation, for instance.
This would be mandatory in case an output transformer was replaced.
As for the VAC reissue, I wonder if the sound would improve by replicating the "error" of the original 8B. Food for thought....