Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: texwest on August 20, 2021, 12:22:47 pm
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I just built a 5f1 and used shielded cable to put the NFB switch on the front panel near by the pot. It doesn't seem to have created any more noise when in direct comparison with one of my other builds. Now wondering if I even need the shielded cable at all?
I'm wondering if the shielded cable is actually doing anything at all? I know that shielded cable will protect signal wires from picking up extraneous noise. But does it also keep noisy wires from leaking out interference also?
Thanks
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Yes. Your cable TV is in shielded cable so you can't stand near the wire with a portable TV and get useful signal.
Depending on details, your NFB hack may not be leaking enough to matter-- we can't see it from here.
But why ask? 5 minutes with hot iron and scrap wire tells all.
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Haha yeah I know I could just try it.
I was mostly asking to gain knowledge. I know that some people use shielded cable to protect the signal inside that wire before it gets to the first grid.
I was wondering it if also keeps noise inside the wire from escaping and contaminating other sources.
I put the switch kind of between the inputs and pot so I was concerned the NFB signal might add noise to the signal at the inputs or the pot.
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Here's a pic of what I did. It's a on-off-on switch and I'm using the other side of the switch for an extra capacitor to the cathode.
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I put the switch kind of between the inputs and pot so I was concerned the NFB signal might add noise to the signal at the inputs or the pot.
Not noise that would be a problem, but output next to input = oscillation.
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I put the switch kind of between the inputs and pot so I was concerned the NFB signal might add noise to the signal at the inputs or the pot.
Not noise that would be a problem, but output next to input = oscillation.
So bad idea? Based on picture is it far enough away to not be a problem?
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Yes it's a bad idea. Good designers don't put strong output signal next to weak input signal. But if it ain't causing any grief, just let it be.
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Yes it's a bad idea. Good designers don't put strong output signal next to weak input signal. But if it ain't causing any grief, just let it be.
I figured if it causes problem I would just use the hole for a switch for the extra cathode cap.
But what about putting this switch on the other side of the pot, between the pot and the pilot light. Would the pilot light cause any problems? The switch has the output signal for NFB and a cathode cap that goes to V1B.
Thanks for the responses!
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Better
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Better
Thanks. Would the 6.3 VAC from the pilot light be a problem for the V1B cathode cap connected to the switch?
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Bear in mind that there’s a 6.3VAC heater filament inside the cathode :icon_biggrin:
Provided your lead dress is tidy, it should be fine, especially as you’ve probably upgraded to a balanced heater circuit.
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Good point Thanks