Two-Rock TS1 / ELI Ground Loop Hum nightmare

[ocianic]

R.G. - Thanks for the PDF links... I'm studying the 1st one this morning and what a great learning and building resource! Much appreciated

[ocianic]

EDITED

[ocianic]

Well I launched into it and built a test rig with the transformer out of the chassis. Unfortunately no change... it's still humming.
I think there must be a bad component somewhere. I noticed the grid joint at the tube is noisy (the one closest to the top of the board) and microphonic when I touch it with a chopstick... and also a couple of other nearby joints. Not sure if this is normal but I reflowed
these anyway... it didn't help.

I might have to pull the whole thing apart and test each component.

Quite frustrating but I will persist trying to solve this situation.

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[Stevem]

Are any of your coupling caps leaking dc onto a grid?

Set your meter for low AC volts and check to see how much ripple voltage you have on pins 1 and 6, the plates .

You also might try doing the pain in the ass thing of getting a 6 bolt Lantern battery and powering the filament from that .

[markusw]

Did you try a different tube?

[ocianic]

Are any of your coupling caps leaking dc onto a grid?

Set your meter for low AC volts and check to see how much ripple voltage you have on pins 1 and 6, the plates .

You also might try doing the pain in the ass thing of getting a 6 bolt Lantern battery and powering the filament from that .

Steve, I did this test and pins 1 & 6 are showing around 40-50 mv...

[ocianic]

Did you try a different tube?

I did yes, and no difference...

[ocianic]

Edited

[Stevem]

I would say that yes, you could pull 6.3 volts for the filament and the needed small amount of HT voltage and ma off of your amp to power this item.

You would need room in your amp for a 4 pin XLR jack which is what I would use .

[ocianic]

Edited

[ocianic]

Edited

[R.G.]

Guys, I'm trying to understand why Dumble with his original lator used the half wave rectifier and not a full wave bridge as this method is quieter?

In this one instance, AI was not hallucinating. The difference between half wave and full wave rectification is that the charging pulse to the filter capacitor come twice as frequently. For math reasons, this means you can get the same ripple voltage for half the capacitance, or half the ripple voltage for the same capacitance. This trade off generally means that designers use full wave except for three reasons:
1. The amount of power used is quite small, and the cost of a bigger filter capacitor is not a limitation.
2. The circuit grounding is critical; full wave bridges necessarily mean that the transformer secondary before the rectifiers cannot be connected to signal ground.
3. Economy (that is, being cheap) in that you can buy three fewer diodes.

I don't know why the designers used half wave. Presumably they thought it was enough.

[martin manning]

Guys, I'm trying to understand why Dumble with his original lator used the half wave rectifier and not a full wave bridge as this method is quieter?

The D'lator uses a full wave doubler. Both halves of the AC wave are used to charge the reservoir caps, and the ripple frequency is 2x line frequency, like a FWB.

[ocianic]

Edited

[ocianic]

Hum eliminated! Next is converting the heaters to DC. Thanks so much to all and especially Steve for suggesting this test with the lantern

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battery.