Amp Sounds Better on 4-Ohm Tap

[The New Steve H]

What does it mean if an amp plugged into an 8-ohm speaker sounds better (less distortion, in a good way) on the 4-ohm tap?

[Reeltarded]

it means that you prefer more dampering..

[The New Steve H]

The amp I'm talking about is a 4-tube version of the Little Wing (6BM8). The only problem with the amp is that when I crank it way up, it develops a type of distortion that sounds a little bit like an organ or synthesizer. I was told that the problem might be the low-current PT I used (100 mA, Classictone 4-18085). Today I noticed that the problem is not as bad on the 4-ohm tap.

It sounds great at lower volume.

I have an Edcor EM0827 (250 mA) I can put in, but I am not eager to do all that work if the PT isn't the issue.

[Reeltarded]

What amp? 4 what tubes? 100mA is pretty slight...

[The New Steve H]

I took this schematic and pretty much doubled everything after the coupling caps, except that I stuck--do not ask me why--a separate PPIMV with 2.2M resistors on each OT. I didn't know how much current 6BM8s sucked at the time.

The rectifier is a 5AR4, not a 5Y3.

[Reeltarded]

You nut! Amazed that it works!! lol

uhh.. i would undo half of everything after the coupling caps and pull one of the MVs.. you trailblazer! Scared to ask what it does with the volumes unequal. I think you already answered that though, maybe?

[The New Steve H]

I'm still rooting through what I did. The big cathode resistor on the power tubes is halved.

I just checked the PPIMVs. It looks like turning one down does absolutely nothing. It seems to listen to whichever knob is turned up the most. If that's possible. Not sure what I was smoking. I am looking at the wiring, and it doesn't look normal at all. I am going to draw a little schematic of that part and see if I can figure out my own logic. I was hoping to be able to run one OT and two tubes at a time.

If it serves to bring anyone's blood pressure down, my last amp is really good. I took it to my music teacher and he could not stop talking about it. He even put some sounds on video for me.

[The New Steve H]

Looks like I did not use the 6BM8 triodes. The preamp stuff is just like a 5F6A.

[Reeltarded]

Not laughing at you buddy. I go off the ranch lots of times myself. you are off the map on this one. hehe

Not sure what the goal of running a side at a time is? What you have prbly works with a little more current cap and ditch the PPIMVs.. but doubling outputs doesn't really do much anyhow. Stand a little closer or build a cabinet that you wear on your head.

[The New Steve H]

I guess I wanted to run one side to get lower volume without engaging the PPIMV. I think I had the idea that the PPIMV affects tone.

It looks like I attached the grid resistors to the unused triode cathode pins on the 6BM8s and then ran the PI output through the PPIMV to the cathode pins, so it goes PI-PPIMV-cathode pin-1.5K resistor-pentode control grid.

Not sure if that was bright. I would hope the voltage on the triode cathode would have no effect on what happens in the pentode.

[The New Steve H]

I think maybe I discovered that it was not possible to isolate two tubes, so I left the two PPIMV pots in there and gave up. If that is correct, I guess I can yank one and put all the inputs on the other. I'm going to jump them and turn on the amp and see if anything explodes.

[Reeltarded]

uhhh hold on a minute..

I wouldn't do that. Draw something that makes lots of sense first.

[The New Steve H]

Haven't done anything yet. I'm still looking the PPIMV over. I am afraid I stuck the wrong size pots in there.

[The New Steve H]

Either that or the damned things are paralleled.

[The New Steve H]

I drew up a pretty revolting schematic of the output section, and the PPIMVs are, in fact, paralleled. I think this is because I only have two outputs from the preamp. They have to feed two PPIMVs, and that means putting a fork after each coupling cap, and each end of the fork goes to the + side of a pot, so you have two 250K resistors off the same coupling cap, with the other ends of the resistors going to ground.

I know the Twin Reverb feeds four output tubes off two PI outputs, but it doesn't have one PPIMV, let alone two. I don't know how you can fix this. My wild guess would be too add two more coupling caps in parallel, but I can't even guess what problems that would cause, and it might mean a whole new circuit board.

Since the PI output signals are already mashed up together, it APPEARS that I can combine the inputs from V4 and V5 on one end of a two-gang pot, with the inputs from V6 and V7 on the other end.