Sovtek Mig 60 artificial center tap?

[evil79]

I was wondering if adding an artificial center tap on the heaters would be a good idea on this amp. I can post a schematic if need be. Thoughts?

[Enzo]

Is there already a REAL center tap?

[nickb]

Given that the heaters are elevated to the same voltage as the plates of the output tubes it not only not possible (without some other mods) but probably pointless as the hum will be reduced by the elevation anyway.

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[evil79]

No, no real center tap. I'm getting some hum when i crank it lately. I have missed this thing to hell and back and it sounds great now. But since I put in a new OT and did a PPIMV, I've noticed it's a little testy. There are dc heaters on V1 and V2. I also didn't use shielded cable on my dual pot MV, so maybe that's a contributing factor. I also just dropped the filament voltage because i was getting like 7.5V and over. Just trying to make this thing behave.

[evil79]

*modded, not missed. Stupid auto correct

[evil79]

Well, those are the DC heaters for V1 and V2. V3-V5 are AC. Those are the ones I'm talking about. Does that matter? This power transformer has always kinda confused me.

[dstrat]

well I would not call those DC heaters really more like extreme elevated AC heaters. and not real sure to the reasoning here.. not a good design IMO. but it is what it is.
A resistor added in series at the junction of R31 and C21 to lower that High HT from being on the heaters.
there is not much benefit of over >70VDC for elevation on preamps.

are you wanting to do something with heaters feeding power tubes? would not likely do what you want.

[nickb]

No, no real center tap. I'm getting some hum when i crank it lately. I have missed this thing to hell and back and it sounds great now. But since I put in a new OT and did a PPIMV, I've noticed it's a little testy. There are dc heaters on V1 and V2. I also didn't use shielded cable on my dual pot MV, so maybe that's a contributing factor. I also just dropped the filament voltage because i was getting like 7.5V and over. Just trying to make this thing behave.

OK. So your problem is hum and likely related to the change in wiring after the power transformer swap. That is the area you need to focus on for a first guess. What does it sound like? AC Heater noise is a soft hum at 60Hz. Rectifier noise is buzzy at 120Hz and all the harmonics. This design is complicated by having rectifiers in the heater path too.

I suggest you look at your new wiring critically. If you don't spot anything I think I try running the tube off an external DC supply as a diagnostic test. It's is going to be tricky with this design and will require some thought.

[dstrat]

yeah I was looking at an obvious wrong schematic I saw MIG50 so I looked up the whole schematic. sorry if my comments are off.