Quick question as virtual center taps are new to me…
I would like to provide a CT for the 6.3V heater for the driver tubes on my amp. The easiest place to add these is at the power transformer. My question is, can I ground the two 6.3V CT resistors directly to the center tap lug of the high voltage secondary on the PT?
It seems like this would be fine as the HV CT goes directly to ground; however, this is new to me and would love to hear your thoughts!
I would like to provide a CT for the 6.3V heater for the driver tubes on my amp. The easiest place to add these is at the power transformer. My question is, can I ground the two 6.3V CT resistors directly to the center tap lug of the high voltage secondary on the PT?
It seems like this would be fine as the HV CT goes directly to ground; however, this is new to me and would love to hear your thoughts!
Between the secondary HV center tap and first PSU smoothing capacitor negative point -relatively- large charging current spikes flowing.
NEVER tie here ANYTHING (including grounding!).
Usually the PSU grounding point is the second PSU smoothing capacitor negative point. This point connected to "main" grounding point/lug via short wire.
This point connected to chassis metal part via hum block.
If you have CT heater (PSU coil or virtual CT point), can be tied its to "main" grounding point.... if the tube's cathode static voltage not too high.
If it high -depends of the tube's datasheet- (for example cathode follower, cascode "upper" tube etc.) the heater CT MUST to tie to cathode!
BTW sometimes the filament elevated from ground (about 1/4 .. 1/3 of B+), the filament CT point connected to voltage divider of PSU.
NEVER tie here ANYTHING (including grounding!).
Usually the PSU grounding point is the second PSU smoothing capacitor negative point. This point connected to "main" grounding point/lug via short wire.
This point connected to chassis metal part via hum block.
If you have CT heater (PSU coil or virtual CT point), can be tied its to "main" grounding point.... if the tube's cathode static voltage not too high.
If it high -depends of the tube's datasheet- (for example cathode follower, cascode "upper" tube etc.) the heater CT MUST to tie to cathode!
BTW sometimes the filament elevated from ground (about 1/4 .. 1/3 of B+), the filament CT point connected to voltage divider of PSU.
You should get away with that, yes. Ideally we don't connect anything to the HV CT other than the rectifier, as euro21 said, but since it is only the heater supply it is not such a sin. Alternatively, ground the resistors directly to chassis.
But:
If this this a functioning amp, why do you think the heater supply needs altering?
Thanks @euro21 and @Merlinb!
The amp is fully functional and it's my first build from scratch. The schematic is below, I've annotated my changes in Blue, please disregard the voltages in Red.
In the schematic, it shows one leg of the 6.3V filament winding going to ground. I imagine this is connected to the same point as the HV CT. Currently I do not have the leg of the 6.3V filament going to ground. To that point, does it matter which one?
That said, I was just curious about lowering the residual hum and remember reading about virtual center taps and elevating heaters as a way to do this. The layout is tight and was hoping to keep things tidy so I'm considering my options to get the CT to ground. Since the HV CT is going directly to ground, I was thinking I could run the resistors from the lugs of the 6.3V filaments directly across the transformer to the HV CT. It would save some wiring...
The amp is fully functional and it's my first build from scratch. The schematic is below, I've annotated my changes in Blue, please disregard the voltages in Red.
In the schematic, it shows one leg of the 6.3V filament winding going to ground. I imagine this is connected to the same point as the HV CT. Currently I do not have the leg of the 6.3V filament going to ground. To that point, does it matter which one?
That said, I was just curious about lowering the residual hum and remember reading about virtual center taps and elevating heaters as a way to do this. The layout is tight and was hoping to keep things tidy so I'm considering my options to get the CT to ground. Since the HV CT is going directly to ground, I was thinking I could run the resistors from the lugs of the 6.3V filaments directly across the transformer to the HV CT. It would save some wiring...