Hi all,
I have a HIFi brand KT-88 tube amp. Its kinda unknown and google doesnt get much info when i search for it.
Its point to point wired, pretty nice to. I replaced all the cheap wiring and installed TJ Jensen Foil coupling caps. I also replacedall resistors with NOS Allen Bradley JAN resistors.
I noticed that on the pre amp tubes (6J8P) there is a 390k resistor to ground on the same pin where the audio signal is connected from the volume knob.
I played around a bit with different values and when i went to 600k the sound really opened up. Does anyone know what kinda value is normal in this spot?
I have a HIFi brand KT-88 tube amp. Its kinda unknown and google doesnt get much info when i search for it.
Its point to point wired, pretty nice to. I replaced all the cheap wiring and installed TJ Jensen Foil coupling caps. I also replacedall resistors with NOS Allen Bradley JAN resistors.
I noticed that on the pre amp tubes (6J8P) there is a 390k resistor to ground on the same pin where the audio signal is connected from the volume knob.
I played around a bit with different values and when i went to 600k the sound really opened up. Does anyone know what kinda value is normal in this spot?
Well I'm guessing you mean a resistor from the grid to ground. That is needed to bias the valve but the value isn't critical and works (at AC or signal conditions) to define the low frequency roll off of the stage as it forms a filter with any input coupling caps. So increasing the resistor means that the low frequency cut off point is lowered... all other things being equal.
Is that what you mean ?
Is that what you mean ?
resistors is a very very deep problem .Your experience seems to confirm mines ... did you try an higher wattage : twice the half value serial connected ? (but twin wattage)😉
Thanks for both replies. The pin where the audio signal is wired to also has a resistor soldered on it that goes to ground. I figured it determes how much of the signal is allowed to reach the pre amp tube.
I used two 300k resistors in series and the improvement in sound is enormous, hence the question 🙂
I used two 300k resistors in series and the improvement in sound is enormous, hence the question 🙂
There really is no "normal" value there. It depends on the design goals for input sensitivity and needs of the pre tube.
All you have done is up the resistance in parallel with the Vol. pot which will make it more sensitive. The volume will rise more quickly and come up to your normal listening level on a lower number. But you will also reach the clipping point at a lower volume number, too.
An audio taper pot gets higher resistance more quickly as you turn it so you will also be compressing that value into a narrower band on the volume control.
I'd undo it.
HTH
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I know , thats the problem : if you TWICE the wattage, it'll be TWICE enormous, any explanation from DF96 won't explain anything 😛 (i've been trying 5 watts, and even 10watts : endless limit ... 😱 )
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If this gives the user the psychological impression that the sound has "opened up" and that the "improvement" is "enormous," then it's a cheap and easy one compared to the usual audiophile snake oil.
I'm sure someone has and reported the fantastic (literally) results to all of his friends. His wife in the next room may have even commented on the startling improvement.
We're trying to help you understand what's most likely going on. You may not like the answer, but it is nonetheless the answer.
Chill out. Go with the flow. Nebulous superlatives combined with adjectives greater that 3 (make that 2) syllables should be controlled at all costs.
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Oh... Thats helping.....
If you put a audio line signal on a pre amp tube pin, and also connect a resistor to ground on that same pin, you are leaking that line signal to ground.... The value of the resistor used defines how much signal is leaking to ground. Thats all i'm saying.
So i soldered a 300k resistor to that pin and exprimented by adding different values. When i used 600k it sounded better, it had alot more detail in highs.
My question seems logical
If you put a audio line signal on a pre amp tube pin, and also connect a resistor to ground on that same pin, you are leaking that line signal to ground.... The value of the resistor used defines how much signal is leaking to ground. Thats all i'm saying.
So i soldered a 300k resistor to that pin and exprimented by adding different values. When i used 600k it sounded better, it had alot more detail in highs.
My question seems logical
Dephazer, take a read through this short thread. Maybe it will help.
http://www.diyaudio.com/forums/tube...id-leak-resistor-value-partly-subjective.html
http://www.diyaudio.com/forums/tube...id-leak-resistor-value-partly-subjective.html
Its getting there 😉
Not exactly... there's more to it than that. The resistor forms an attenuator in conjunction with whatever source impedance is feeding your resistor. It doesn't leak signal away... at least we would never describe it that way. If your source were a solid state stage (CD player say) then 300k, 3meg or 3k, all would have no effect on the signal.
Not so much, no. You have to understand how the tube operates. The grid draws little to no current. All that resistor does is makes sure that the grid is held at zero potential at DC. It has a side effect of altering the volume control tracking, and that's potentially significant- not for actual sound, but for how you're perceiving it.
A similar effect is often reported if a volume control tracking requires it to be turned past (say) 2 o'clock to get reasonable volume- users will complain about "squashed dynamics" even though there is in reality not a smidge of difference in the sound compared to a different control tracking that gives the same volume at (say) 10 o'clock.
If there's a capacitor coupling, changing the grid leak can also change the low frequency rolloff, which is generally subsonic.
Well, your question was "Does anybody know what's "normal."
Look at it this way. If you turn the volume control down all the way you have "0" ohms at the grid to ground. It doesn't matter what the value of the other resistor is. You don't even "need" the other resistor. You will have a range of reststance from 0 to the max of the volume control. You can then choose to swap out the volume conrol and substitute a fixed resistor at the volume level you prefer. Now, if you found that you liked a new listening level above the old maxed out level, because you have added more resistance that only comes into play now above the old max level, then you have indeed found a wonderous new quality of sound for your amp. But you have only increased the maximum grid leak resistance available, not the quality of the signal at the old listening level's resistance value. Just turning up the volume a little more would achieve the same result. Did you listen all the time with your volume control maxxed out?
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