Question about paralleling triodes

[big-ez]

I have an amp that only uses 1/2 of the first preamp 12AX7. It's pretty hissy, so I thought I'd try paralleling the triode. I know that to keep biasing the same, I should halve the plate & cathode resistors, and double the cathode bypass cap. Can I simply add new resistors/caps of the same value in parallel to existing ones? Eg, can I add a 100K resistor in parallel to the existing 100K plate resistor (to make it 50K), and parallel another 25uf cap across the existing bypass cap (to make the value seen by circuit 50uf)? This will make the mod easy to reverse. Are there any downsides to this? Might this approach add more noise since I'm using more components? Thanks a ton in advance.

[Willabe]

What amp and can you post a schematic of it?

[big-ez]

It's a Dr Z Jetta. I don't have a schematic, and the noise isn't terrible. I guess I'm just a little bored and looking to do some experimentation. It's the first stage of amp, only uses 1/2 the 12AX7. 100K plate, and 2.2K/25uf on the cathode.

[vampwizzard]

We discuss triode paralleling in this thread https://el34world.com/Forum/index.php?topic=23769.msg259346#msg259346 and if its noisy its unlikely to be solved by the paralleling. You get MORE gain therefore more noise. It is a negligible but slightly noticeable difference.

[sluckey]

Just do it. Probably take 5 minutes. You got time, right? Tell us what you think.

[big-ez]

Many threads I read on this (not just here) say you get a 3db reduction in noise due to better STN ratio. Gain increase should be ~30%. I have done the research, and I will test this out. My question is: is it OK to just parallel those new components on top of existing ones, or is there any reason I should not do that and rip them out and put in the exactly values I need?

[sluckey]

My question is: is it OK to just parallel those new components on top of existing ones

yes. There's really no need to double the bypass cap though.

[kagliostro]

Many threads I read on this (not just here) say you get a 3db reduction in noise due to better STN ratio.

Yes, but the noise reduction is referred to the noise that incomes from the imput, not noise inducted by heaters or other sources

Although, maybe you'll like the response in "tone" of the paralleled input

Franco

[big-ez]

I just wanted to provide an update: I tried this and noise increased by a decent amount. I didn’t get a sense that volume or output went up by much. Haven’t had a chance to measure voltages yet but will do tomorrow. I will just reverse the mod if I can’t get it any quieter. Thanks for the help!

[kagliostro]

As vampwizzard told

We discuss triode paralleling in this thread https://el34world.com/Forum/index.php?topic=23769.msg259346#msg259346 and if its noisy its unlikely to be solved by the paralleling. You get MORE gain therefore more noise. It is a negligible but slightly noticeable difference.

I think you must try to eliminate the noise before you parallel your inputs

Franco