Plexi 6V6 build MV

[dude]

The AO-43 chassis to a Plexi 6V6, 6L6 and EL34 has a MV just before the PI, 1 meg A pot. Seems like I can't turn that Master much past half without overloading the PI and squeal, not a real big deal the amp is loud enough using the two vol pots. But I was thinking of replacing it with a 500K pot, would this give me a better range or feel on the Master volume. Since I used the original bd things are tight, to get that MV pot out I have to lift the board, I know I didn't plan well enough. So, if I put a 1 meg R across the outer legs of the 1 meg master, in parallel, that will change the 1 meg to a 500K. Any foreseen problems doing this and would this be worth doing in my case..?


Also, maybe I should use shielded wire to the Master and forget the 500K pot...?



The MV is just a simple pot before the PI.



al

[shooter]

without overloading the PI and squeal

this is where scopes win, you don't have to guess, "oh, I need a bigger voltage divider, or, or
Are you sure it's gain, and not FB
I spend most of my "up-front" time dialing the output of the pre to just where I want it, then I dial tone, then I tear it all apart n build again 

[sluckey]

How does the amp behave if you disconnect the NFB wire?

[dude]

The same but slightly a little more beef.
I haven't been playing the 6V6 Plexi lately but my TMB SIII (Trinity schematic, EL84s), which is nowhere as bright as the 6V6.


There seems to be a little too much "gain" in the 6V6 plexi and very, very bright, turning down the treble to "off" the brightness is still too bright,even with the bright channel on 1 or 2, turning up the normal channel helps, also on 2 or 3 but I have to have the Master vol no more than half on these setting as the amps gain is too high.


The treble in this amp is way too ice picking bright, turning up the treble causes the squeal. The cathode caps on normal channel 820 and 22uf (not 220uf) and bright channel 2K2, .68uf. The second gain stage cathode is 820, .68uf, I think that is what your schematic calls for. I followed yours and Hoffman's basically the same.


From  plate .0022uf to bright Vol with a 330p there, not 500p bright cap 120p on the bright vol.  Everything else follows teh schematic.


So, the only deviations from your schematic are the 22uf and the 330p, schematic calls for 220uf and 500p. No bright cap.  And I didn't have a 2k7 Handy bright channels cathode  it's 2K2.


I know this might be hard to follow but appreciated suggestions, just want to cut the ice picking, I play with a strat, bridge and neck together, single vintage coils, not hot.


EDIT: I was thinking maybe changing that coupling cap to bright channel from .0022 to .0047 ...? or taking the 500p out completely on bright channel...? Of course the speaker has a lot to do with brightness, the Weber Blue Dog is very bright, a GH12 isn't as bad..?


Just give me a clue best way to knock off some of the biting brightness, don't say turn the bright channel down as then that affects the Mids on that channel I like.


al

[dude]

I think I got it, took the 120p bright cap (not on schematic) out. The big change was the coupling cap to the bright vol. from .0022 to .0047 big difference. The master volume works much better, too, no squeal all the way up works as it should. On 1,2 the treble is noticeably cut now, treble range works much better. I will probably go back to the 470p (330p now) on voltage divider to bright vol.


Now that I cut that ice picking brightness, I might even try a .0033 coupling cap (probably not much difference from original .0022). Also, I should at least try a 220uf on the cathode of the normal channel. The magic is blending the two volumes and then setting the master, I'll have to try that PPIMV when I get a good pot. My dual pots have different readings, someone must sell a more accurate dual gang 1M A pot...?


Big problem for me is a strat, single coil vintage p/u's and Blue Dog Alnico's, the guitar and speakers have a lot to do with brightness and tone, too.