Filament CT grounding on MKIV

Dynaco-Doctor Forum

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As I had stated in my previous post, I just got my first MKIV. Trying to familiarize myself with the internal wiring, I noticed that the green/yellow wire (filament center tap) is connected to lug #2 of the five lug terminal strip, which is not grounded. I thought that this might be a mistake, so I read the wiring instruction in the manual. Step number 5 states that this wiring is correct, however when you get to step #15, you are instructed to solder a small wire from lug #2 to lug #3, essentially grounding the filament center tap. However, it goes on to say that if you are going to use the MKIV with a PAM1 preamp (mono), do not make the grounding connection. The reason that I brought this up is because when I first measured the AC output (hum) on the 8 ohm tap, it was close to 2.4 mv.Not exceptionally high and barely noticeable, but should be lower. I then grounded the green/yellow wire (filament center tap) and the AC (hum) went down to .6 mv AC, totally inaudible on my 100 Db 1w/1m speakers. So unless this subject has already been discussed to death (couldn't find it in a search), I hope that it might help someone to really quiet down their amp. Good Luck, wpod

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Topic - Filament CT grounding on MKIV - wpod 06:47:01 12/24/05 (2)

Re: Filament CT grounding on MKIV - zacster 08:38:04 12/24/05 (0)

Normally it's "AC" grounded through a cap(nt) - Russ57 06:57:37 12/24/05 (0)

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