New 5F1 build: some voltages

[Chuck H]

A filament CT is a bonus and should be used! That is, unless you're going to make a humdinger circuit; but that's really for the builder who wants to exorcise the last fraction of a decibel (centibel? millibel?) of heater hum.

I'm told one or the other works fine (CT or the resistors), no need to use both. Certainly not recommended would be to reference one of them to ground and the other to some different potential, like the output tube's cathode.

Merlin's preamp book gives some theoretical and practical insight to heater referencing (and he seems to be a proponent of the humdinger). Raising the heater reference to the cathode, about 20 - 23vdc (?) in a 5F1, may make a difference. I haven't tried it yet. Will do when I get around to that last centibel of hum, though!

I once used a SF Vibro Champ as a platform for a custom build. The finished amp used a twisted pair with the false CT referenced to the top of the 6V6 cathode. Virtually no hum. Very satisfying.

[g1]

If you use both the heater CT and the virtual CT resistors, the resistors don't do anything other than putting an extra load on the heater winding. They only help if there is no CT for the heater winding.

[Chuck H]

If you use both the heater CT and the virtual CT resistors, the resistors don't do anything other than putting an extra load on the heater winding. They only help if there is no CT for the heater winding.

I'm only addressing this because it was posted as a reply (I had to change viewing modes to check ). I don't wish to be misleading. Was I too ambiguous? I know I didn't state directly that I used both the winding CT and a false CT. Or am I confused (it happens).

[Jonny toetags]

Correct me if I'm wrong, but I'm guessing from the layout that the heaters have one leg grounded at the PL just like Leo did. It'll give you less 60Hz hum if you take two 100R resistors and make an artificial center tap for the filament supply.

Also, any SE amp will have less ripple rejection than a PP amp, the only fix for that is to add more filtering. Back in the day, can caps were expensive, so Leo (again, as any self-respecting entrepreneur would do) used the least amount of filtering he thought he could get away with. Personally, I'd put the biggest res cap in there that the rectifier tube allows, and move the 16u cap over to the screens. That will reduce any hum that sounds like a 'buzzy' 60Hz.

Those are the two primary sources of 60Hz-and-harmonics noise in that amp. Which one predominates depends on how bad the heater hum really is.

I used this layout exactly, so I'm going to ground with the 2 striped wires.
So you're saying I should remove one and use an artificial center tap?
What would be the proper way to do that?
I understand the idea, but I've never actually done it? Specifics are good

[g1]

I'm only addressing this because it was posted as a reply (I had to change viewing modes to check ). I don't wish to be misleading. Was I too ambiguous? I know I didn't state directly that I used both the winding CT and a false CT. Or am I confused (it happens).

Sorry Chuck, my comments were directed at Dr.Gonz's post #13, I should have used the quote button.

I used this layout exactly, so I'm going to ground with the 2 striped wires.
So you're saying I should remove one and use an artificial center tap?
What would be the proper way to do that?
I understand the idea, but I've never actually done it? Specifics are good

No, eschertron was referring to the original Fender design where the heater winding did not have a center-tap and one side was grounded. You have a center-tap and it is grounded so you do not need the resistors.
However, you could try elevating the heater winding to see if it helps your hum. You would disconnect the grn/yel from ground and connect it to the 6V6 cathode (yellow wire at 470 ohm 5W resistor).

[eschertron]

I used this layout exactly, so I'm going to ground with the 2 striped wires.
So you're saying I should remove one and use an artificial center tap?
What would be the proper way to do that?
I understand the idea, but I've never actually done it? Specifics are good

No, eschertron was referring to the original Fender design where the heater winding did not have a center-tap and one side was grounded. You have a center-tap and it is grounded so you do not need the resistors.

Ah, so now I see the green/yellow wire on the page. I spoke out of turn, and I apologize