Using my O-scope on Tube amp

[dhaen]

Paul,

You say that the attenuator in mounted on an unconnected plate?
That plate should go to star ground!

Cheers,

[TubeHound]

Ok, ok ,ok sheesh. I'll solder a wire

Thanks John

[dhaen]

Paul,

A general rule should be:
If it's conductive, and not already connected to anything, earth it!

Cheers,

[fdegrove]

Hi,

Well done John.
Now if that pot is sitting where I think it is, namely the top copper plate, then that would explain a lot.

I assume the grounding has been done on the bottom plate which I assume is a copper plate as well.

If star grounding is to be applied,both should be connected at the same point.

Then we can at long last tackle the 7.2 heater voltage.


Good luck Paul,

[TubeHound]

Hello,

Well I tried everything I could think of or see. I solder wires to ground all chassis plates to star ground. I removed all the ground wires from the shielded wires, ( thought this might be introducing a/c back through ground). Tried the snubbers, no difference. Soldered a wire to connect the two star ground points together, ( but the copper plate makes that a mute point).

I believe my alternative is to make all filaments d/c, but really do not know. I could try this, I believe this is a matter of buying some filament trannys. Would this leave my PWT unloaded to the point that voltage on the B+ would rise because of less current draw?

Any other Ideas and new suggestions?

Should I sell them to Frank or John for $1.50?

[dhaen]

Paul,

Let''s move back 1 step.
You said that when you held the volume pot, the spikes disappeared. Is that better now?
If not. then it cannot be earthed.

John

[Tomatito]

Soldered a wire to connect the two star ground points together, ( but the copper plate makes that a mute point)

If they're both making contact with your copper chassis you could have the makings of a ground loop ?

just my 2c worth.

good luck

Martin

[dhaen]

Martin,

Yes indeed it could be that issue causing the slow (sinewave like) hum. We haven't got that far yet We're still trying to sort out the "spikey" hum

Cheers,

[TubeHound]

Hi,

Sorry I have been gone awhile. Life has a habit of taking up my time and attention.

Now I do not know if I have been missed, but I am sure glad you guys, ( and gals?) are out there.

I have been thinking about the grounding in the JE 300b's and I did use two star grounds. Both are directly coupled to the copper chassi and are not isolated from each other or from the a/c mains safety ground. What if I isolated the two star grounds above the chassi and from each other? Leaving only the a/c mains earth connected to the chassi for safety?