Parallel

[davidwpack]

Ello! I've been practicing load lines of some of my previous builds. Recently, I've modified one of my builds by paralleling the plates and grids of V1-A and V1-B. I'm wondering how you factor this in when graphing load lines. For example; I used a 50k for the plate load. In Merlin's book it looks like he explains most of what I'm trying to figure out, however, I kept the cathodes separate with an 820R and 1.5K on both V1-A and V1-B respectively. It looks like I'd have to do 2 graphs separately. Am I right about this? I'm hoping this question makes sense. Thank ye!...Dave

[jjasilli]

Yes, you need 2 separate load lines.  The twin triode is the equivalent of 2 separate tubes in one bottle.  The Plates don't know or care that they're sharing a plate resistor.  Because ea side is pulling its own current, the 50K plate resistor looks approximately like 100K to ea side (adjusted for actual current draw on ea side).  Because the cathode resistors are different, ea side is pulling different current.  So you need to plot ea loadline for the actual current draw. 

[davidwpack]

Okie. That's about what I was thinking but wasn't quite sure. Thank you!

[PRR]

There's not a simple analytical answer.

Why do you need load-lines? It will work. Build it and try it.

Here's a detailed analysis of parallel triodes of different Mu/perveyance. It could be adapted for similar triodes of different bias. Actually you could SPICE *your* problem in a jiffy. But if that has not occurred to you, it isn't worth the learning curve. (After 20 years, I still fumble SPICE.)
http://www.dmitrynizh.com/parallel-triodes.htm

[davidwpack]

Hey, thanks for the info! I guess I just find it interesting to see a visual representation of why something sounds good...or in some cases, not so good. Plus drawing a bunch of lines gives me something to do when getting through 24 hour work shifts...and it's kinda fun.