Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

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RE: wait a minute

Posted by Tre' (P) on December 30, 2019 at 08:26:30

In Reply to: RE: wait a minute posted by Aristarchus on December 29, 2019 at 19:01:22:

"The proof is in the pudding. Just try different fuses and see if it makes a difference to you."

That is almost impossible to do for many reasons having do to many things including expectation bias. People always say "trust your ears" but that is a mistake. The human ear/brain mechanism is too easily fooled.

Don't burn your house down but try this. If you think the fuse is causing some kind of audible problem then get rid of it (as a test). Connect a short piece of 20ga wire across the fuse holder. Now there is no fuse to mess up the sound. Clearly it would not be safe to leave it that way but at lease now you know what the unit sounds like when there is no fuse to "mess things up" and now you have something to "shoot" for when picking which fuse to use.


"I'm wondering at what point the amount of inductance in a resistor creates an oscillation problem 20nH, 30nh, 25.5nH? Or likely not at all, like some people think? People who do know how electronics work. Like Ralph."

It will be a case by case thing. It will depend on how much stray inductance there is in the wiring before the tube's grid and how much Miller capacitance the tube being used has. There is no single answer to your question.

Ralph is wrong. A grid stop resistor does not stop the oscillations because of the low pass filter created between the total source impedance and the Miller capacitance. A grid stop resistor stops oscillations because it adds resistance to the LC tank circuit.

"The use of a carbon comp resistor that would effect the sound would also be a mistake, so why take the chance if it isn't necessary?"

There is no chance of a CC resistor "effecting the sound" when used in the grid stop position but many times grid stop resistors are not necessary.

What circuit are you using and why are you concerned about grid stop resistors? Why do you think your circuit needs grid stop resistors? Is your circuit misbehaving?

A 2hz f3 is only needed/useful if your system and speakers and room fully support 20Hz. In the low frequencies there is always a lot of phase shift do to speakers, room interaction (and with tube amplifiers) output transformers. Very few systems go down to 20Hz and none of them do so without phase shift.

Tre'


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