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Can i sub a 50K for a 100K volume control?

DAK808

Member
2012-05-27 7:34 pm
I have a 2 x 6sn7 preamp that has a bad VC. The original is a Noble brand, that has worked well and I found another Noble that is the same size except it is 50K. Would there be much of a change for the different value VC? I don't want to go through all the trouble of installation as it is a tight fit. Thank you for your suggestions. cheers, 808
 

DAK808

Member
2012-05-27 7:34 pm
Yeah, tubes. It is a 2 x 6sn7 preamp. If the difference is only diminished volume, I could live with that since the original preamp would not even crack 11 oclock in my setup. But , if there will be a problem with stability or frequency response then I guess I need to find a good 100k pot.
 
I guess I'm still not clear if the volume control is driven by the tubes in the preamp or if it is at the input (and thus driven by something outside the preamp).

If it is driven by tubes, you should show a schematic of what is driving it. Without that, it is impossible to know. The possibilities range from, "Oh it'll be fine" to "There is no way that will work well."

But if the VC is at the input of the preamp and you are driving it from a CD player, you could go down to a 10k pot easily.
 
Assuming the volume control is at the input of your tube preamplifier:

If your sources are tube circuits (like a tube phono preamp or tuner), then they'll have higher output impedance than if they're solid state sources (like a DAC or CD player).

If the sources have tube outputs with Zout of 5k, then you'll want at least a 50k volume control at the input of your tube preamp. But a 10k volume control would load down the output of that tube source with Zout of 5k ohms.

If you're feeding the output of an original RCA RIAA phono preamp with 12AX7 tubes to the inputs of your tube preamp, then that's a completely different story.

If the sources have solid state circuits with Zout of 1k or lower, then a 10k pot would be fine.

Precise details needed to give you a specific answer to your question.

--
 

DAK808

Member
2012-05-27 7:34 pm
Sorry, no schematic, as it is an AE3 preamp from Audio Electronic Supply, aka, Cary. They don't give schematics, those paranoid bleepers. But, I will track the circuit and let you know if it is on the input side of the tube or between the 2 sections. I am not certain.
 

DAK808

Member
2012-05-27 7:34 pm
The VC is on the input

I guess I'm still not clear if the volume control is driven by the tubes in the preamp or if it is at the input (and thus driven by something outside the preamp).

If it is driven by tubes, you should show a schematic of what is driving it. Without that, it is impossible to know. The possibilities range from, "Oh it'll be fine" to "There is no way that will work well."

But if the VC is at the input of the preamp and you are driving it from a CD player, you could go down to a 10k pot easily.

I checked it out and the inputs go to the source selector switch and then to the VC. Which then feeds the grid of 1 section of the 6sn7 then from its plate it is cap coupled to the second grid.
 
I checked it out and the inputs go to the source selector switch and then to the VC. Which then feeds the grid of 1 section of the 6sn7 then from its plate it is cap coupled to the second grid.

Cool, so it looks like you just have to look at the Zout of the phono preamp. If it is about 5k or less, you should be good to go.

I mean, the main consequence if it isn't is that you would have higher distortion and you might get a reduction in gain from the phono preamp due to the more difficult load and steeper AC load line.