Plate voltages

[iknowjohnny]

These are my preamp/PI voltages. I wanted to hear opinions as to whether anything seems different than you think it should be. The amp is a fairly high gain preamp (about as much as a peavey classic 30 dist channel) with a cathode follower and 2xel34's ala marshall, but my own design in the pre and mostly marshall in the PA. I wanted to ask because I never really knew where to adjust voltages so i have always just put them where it sounds best w/o regard for the correct way assuming there is. I like a clean PA from the PI on, and a clear articulate distortion in the gain stages. I'm good there, but just out of curiosity i wanted to see if anyone sees voltages that they think aren't optimal for this setup.

I also wanted to see what you all thing of parallel power rails like on the matchless chieftain. that to me seems like a much better way because if say you want more voltage at the first stages but don't have enough even with a small value dropping resistor, you can't adjust it up w/o changing the stages b4 it. And if you happen to want those to stay as is, it seems to me only a parallel rair would allow you to change it w/o affecting the voltages of stages b4 it. Thoughts?

V1A:224
V1B:223

V2A:233
V2B:354 CF

PI:
V3A:248
V3B:261

[Jana]

CF looks a bit high. What is the cathode voltage on the CF? About 230?

[iknowjohnny]

Good call....235v. Of course if i adjust the CF with the node that will drop everything after it. Should i adjust the 100k cathode R?

EDIT: OK, i get it now. You coulda just told me i'm an idiot instead of just being silent.
So i guess it's i have only 2 choices to lower the CF voltage....lower the node and affect the rest of the stages downstream, or use the parallel rail i mentioned. I think i killed my tung sol reissue due to the high voltage so i suppose i should use a bigger dropping resistor and hope my gain stages aren't too affected. I don't like the way they sound when the voltages lower tho. I'd actually prefer more which again speaks to the parallel rail. Do all matchless amps use that?

[rp]

I'd actually prefer more which again speaks to the parallel rail. Do all matchless amps use that?

Ahh - now i get it. The lighting and spitfire do and I just built a lightning and didn't even give this much thought though I did pause at it in the schematic - talk about painting by numbers or sleep walking through a build. But now that I know what it is it seems like a great idea. Darn easy to tweak the voltages at the individual stages. So what's the disadvantages? Obviously downstream tubes don't get the benefit of all the smoothing that came before it in a series string but if you have what you need... and apparently the matchless do. Are most of the old amps done in a series string cause caps were big and expensive way back when and it was best to add all the filtering up?

[iknowjohnny]

I dunno, but i do have a lot of filtering. I have 100uf for every node, PA and pre except V1 which has 60uf. Oddly my amp is not stiff at all. But whats bizarre is that i tried big filters in it a while back and it WAS stiff. I don't recall what i did that changed the way it reacted tho, but i HAVE made a zillion changes to this thing.

[Jana]

Being silent? Some people work, lol.

Yeah, as you found out, Tung Sol RI won't handle those voltages.

You can raise the heater voltage reference to get a little more safety margin--it is the heater to cathode voltage you are trying to reduce.

Raise the heaters up to 50 volts and you now have 235 - 50 = 185v heater to cathode voltage. Still too high for my tastes but much better than 235.

[Structo]

In addition to a stiff feel, when I have tried using higher B+ filtering than the design called for I noticed a bit less sustain on the notes.
Like they were dampened or something.

I was only thinking in terms of tightening up the bottom end.
But there are better ways to do that.

So sometimes too much of a good thing is too much.

[iknowjohnny]

I agree. My tone isn't stiff and all and sounds and feels just wonderful, but it DOES lack the sustain it had before. I may hav eto try removing the extra 40of on the first stage which is now 60uf. I think the 100uf nodes before that shouldn't have an effect on sustain tho.

[iknowjohnny]

I spent a couple hours playing with filtering and heres what i found. First of all i am talking about a marshall style amp with a somewhat high gain preamp. I think that must be stated because i'm not sure how filtering might differ in it's tonal affects between an amp like this and say a fender. For me, the general effect of filtering is that too much and the tone gets thinner and harder, while going with less makes it feel squishier and sound fuller and less harsh on the top.

that said, i noticed that V1, the first 2 gain stages where most all of the shaping of the drive is done, seems to benefit up to around 60uf, and after that it begins to get sorta sterile and thin. V2, stage 3 and the cathode follower sounds good with a ton of filtering. And finally the PI wants very low uf, and once you start adding filtering to the PI the tone really goes to he||. So i will Not sure how typical this is, but with my amp it was quite obvious. So i am going to remove some from the PI but leave the other 2 nodes as is because i already have 100uf on V2 and 60 on v1. So lowering the PI's filtering went a long ways to sweetening up the feel and sustain without leaving it too mushy or inarticulate. The PI now sports a huge 20uf. But the rest of the amp including the PA is higher than most any production amp. Sounds and feels sweet as molasses.