HUMMMMMM

[lowell]

So any theories on how this thing is working without a bridge rectifer? Just full-wave, no CT.

[g1]

Can you draw it? Not sure where or how exactly you would have it grounded.

[lowell]

It's this - take away the CT and the choke

http://electriciantraining.tpub.com/...4179_200_2.jpg

[d95err]

The filtering seems a bit low for a preamp. I would do two things:

1. Increase the 100 ohm resistor to 1k or more.

2. Add another filter node to supply the first preamp stage (e.g. 10k and 22uF).

[loudthud]

It's this - take away the CT and the choke

http://electriciantraining.tpub.com/...4179_200_2.jpg

So you grounded the gray wire? That's a half-wave power supply. The diodes connected to the white wire never conduct. Use a full-wave bridge and connect either the yellow and gray or yellow and white wires. The unused wire should be insulated and not connected to anything.

[g1]

So you grounded the gray wire? That's a half-wave power supply.

That should make for some hum. And a confounding type as it would be 60hz rather than 120.

[lowell]

No, the yellow and gray each go to a diode anode. Both diode cathodes connect to the + of the res cap. Which is grounded to "common" at it's - terminal. White secondary is unterminated. I'm also only using one of the primaries at this point.

* NOTE - This transformer has a purple SHEILD lead. I have this grounded at the output jack. Maybe this is somehow allowing the rectifier to function?

[lowell]

Ok here go: Reminder that the 6V6 is in triode mode.

[lowell]

Dang it...forgot I had modded it a bit. Here go:

[Enzo]

How can that work? What B+ voltage do you get at your first cap, the 100uf?

[The Dude]

Agreed. Did you forget to draw a center tap or something?

[lowell]

Welp... I thought maybe one of the secondaries was accidentally shorting to the chassis...sure enough it was, hence the thing was working, but only half wave rectification.

So rewired it all with a full wave bridge, regrounded all signal and supplies together, and ran that common with ONE wire to the chassis. Then running the chassis to the IEC earth pin with ONE wire. Still lots of hum. I can't believe it's still humming, actually it's humming MORE now haha. Only incorrect thing now is that the input jack is grounded to the chassis, on the opposite end of the unit from where everything else grounds to the chassis. I will try isolating it, but I tried this previously and it didn't help at all.

[Enzo]

Grounded all signals and supplies together. A wire from each to ONE point? Or a common wire going to each thing, and ONE wire from T^HAT to ground? If the common wire is the return path for a filter cap AND a preamp stage, then the ripple will travel through that "ground" into preamp.

But I cannot say it enough: there is hum and then there is hum. Is it 60Hz or 120Hz? It is in the preamp or power p? etc.

[Chuck H]

What he said^^^^^^^^^^^^^^^^^^^^^^^

1) Are you using individual ground leads from each circuit that needs to be grounded. No "daisy chains"???

2) Have you identified the hum frequency???

Also, there seems to be some confusion about how the PT is wired. Loud mentioned that you may have the primary wired incorrectly and you've never answered to that or revisited the subject. You had a secondary "accidentally shorting to the chassis". I don't get how you just discovered that with all the testing. Changes to the primary wiring, half wave type, FW w/no CT (?) and bridge rectifiers would ALL change voltages too. Quite drastically in fact between half wave and bridge, but you haven't addressed that either.

Oh, And don't forget to try different tubes. IMHE a disproportionate number of new Rusky preamp tubes hum like they don't know the words. As in, I buy five if I need three because I usually need to cull at least one. And this is from the vendors, not bulk.

[lowell]

Thanks guys. This is surprisingly challenging.

I honestly forgot to follow Loud's suggestion amidst discovering, stupidly, that one of my secondaries was grounded. I have yet to add the other primary in parallel. Does phase matter when doing so? Or should both black primaries and both red primaries be tied together? Also, why is this important to do?

I rewired my grounding per trobbins suggestion -

Many good threads and articles on grounding - chase a few up with google. Chassis to 0V circuit through only one link. Mains AC protective earth to chassis through only one link.

All my filter caps and signal grounds are connected together, then one wire to chassis ground. The bridge rectifier ground is not connected to this circuitry, but instead goes directly to chassis ground thru its own wire where everything else is grounded. The 6V6 circuitry is technically, physically, tied closer to ground than the 12ax7 circuitry. There's less wire to ground from the 6V6 that is.

The HUM is a combo of 60 and 120hz. If I pull the 12ax7 it's mostly 60hz. If the 12ax7 is in there is way more 120hz. So the 120hz is mostly from the very first preamp stage, then the 60hz is from the 6V6 stage.