Earthing and lead dress
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- Raja_Kentut
- Posts: 64
- Joined: Fri Aug 11, 2023 9:57 am
- Location: Veitsbronn, Germany
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Re: Earthing and lead dress
I fully agree to the above.
In this case we also have HF oscillating. Now next to the resistance of wires we have to think about their inductance. (and also their capacitances)
The inductances can build a resonance with capacitances in the circuit. The tubes themselves have internal capacitances.
Together with the amplification of the tubes this makes up an oscillator.
There are ways to work against this HF :
Use „gridstoppers“ that are resistors directly soldered at the tube sockets at the grid pins.
Use forward and return path wired close to each other, twist them. The inductance of a conductor is larger, the more area you have enclosed with it.
Use little ceramic capacitors anode to ground at the power tubes, soldered directly at the socket pins
In this case we also have HF oscillating. Now next to the resistance of wires we have to think about their inductance. (and also their capacitances)
The inductances can build a resonance with capacitances in the circuit. The tubes themselves have internal capacitances.
Together with the amplification of the tubes this makes up an oscillator.
There are ways to work against this HF :
Use „gridstoppers“ that are resistors directly soldered at the tube sockets at the grid pins.
Use forward and return path wired close to each other, twist them. The inductance of a conductor is larger, the more area you have enclosed with it.
Use little ceramic capacitors anode to ground at the power tubes, soldered directly at the socket pins
Nothing is better than an unexpected discovery that brings you happiness!
Re: Earthing and lead dress
Using the chassis for gnd, you can just make the worst scenario..
I would remove all the gnd wires, connect them only to electrolytic minus terminals where they belong, and ground the chassis only at the input jack. With the bad or random layout oscillations are just normal, telling you how good you are, or not
Speaker ground is tricky here, need to scratch the head little bit. Guess where it is going. It is easy.
It is going to gnd side of 1k resistor in PI (6SL7) where it belongs (not to the chassis).
I would remove all the gnd wires, connect them only to electrolytic minus terminals where they belong, and ground the chassis only at the input jack. With the bad or random layout oscillations are just normal, telling you how good you are, or not
Speaker ground is tricky here, need to scratch the head little bit. Guess where it is going. It is easy.
It is going to gnd side of 1k resistor in PI (6SL7) where it belongs (not to the chassis).
Re: Earthing and lead dress
I think I’m nearly there. The noise on the output jacks is 10mV.
Thanks for your help, your insight and your patience.
Much appreciated.
Thanks for your help, your insight and your patience.
Much appreciated.
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Yours Sincerely
Mark Abbott
Mark Abbott
Re: Earthing and lead dress
this is good, enjoy
Re: Earthing and lead dress
10mV is well minimized, but what is the source? When that is identified it can be not just reduced, eliminated. Even low level oscillations will heterodyne with signal to make the signal less pristine.
Tube junkie that aspires to become a tri-state bidirectional buss driver.
Re: Earthing and lead dress
The shielded cable was the game changer. It made the most difference.
Yours Sincerely
Mark Abbott
Mark Abbott
- martin manning
- Posts: 13208
- Joined: Sun Jul 06, 2008 12:43 am
- Location: 39°06' N 84°30' W
Re: Earthing and lead dress
The usual culprit, the wire from the wiper of the volume pot. This wire would normally be on my hit list, but I thought the builder was on top of this. Everyone makes mistakes.martin manning wrote: ↑Thu Jan 04, 2024 12:39 amWhich was the offending lead, or did you replace more than one?
Yours Sincerely
Mark Abbott
Mark Abbott
- Raja_Kentut
- Posts: 64
- Joined: Fri Aug 11, 2023 9:57 am
- Location: Veitsbronn, Germany
Re: Earthing and lead dress
great!
now you can eradicate the HF, have you experimented with a gridstopper?
now you can eradicate the HF, have you experimented with a gridstopper?
Nothing is better than an unexpected discovery that brings you happiness!