18w, too much sag

[Matty_V]

I just received my recent parts order from doug and have been experimenting with different tubes in my 18w creation. I've attached the updated schematic, I changed some stuff.

With this new configuration I can jack the master volume up to overdrive the power tubes at less than ear piercing volumes, it was too much before. However I get way too much sag, and the volume swell upon recovery is obnoxious. It doesn't do this with the master turned down a bit. I'm thinking it may be the 1K screen resistors, would dropping those help? Or could I just dump them altogether? The only values I have on hand are 820R 3w and 470R 5w

Also with the way my master is, could I dump those 470K's to ground right before it? Grid leaks, whatever they're called. Thanks!

[TIMBO]

Have you tried a SS rect or EZ81?

[OldHouseScott]

You may want to experiment with higher grid stoppers, maybe 22k or even 47k.

[zendragon63]

Hey Matty_V, try what he said. Just a thought: simpleton as I am, I think of 'sag' purely as a function of a drop in voltage due to sudden increase demand in current. And if you have a supply reserve--capacitors or inductors--you can control it. It might have been your intent to cut the power (volume) by not bypassing Rk on the EL84s; it also allows more cathode voltage and current fluctuation when more than mildly overdriven simply because that reserviour is gone. All else being equal...it is just a thought. Sluckey and geezer have done alot of work lifting this cap so maybe they will toss in their $.02.

I have not had as much tonal success using a 12AU7 in the PI with Rp and Rk values that usually more suited toward a 12AX7 but if it is working for you--great. Good luck man. Regards

dennis

[Matty_V]

Thanks I'll give this a try when I get to it. I lifted that cap cause it made the amp sound really sizzley, who knows it may find its way back in there when its all said and done. That's a good explanation. I did have ax7s across the board but I picked up some different 12a_7 tubes and liked this configuration. I may try the at7 for a PI and see how I like that. Just really tinkering with stuff to see what happens.

[phsyconoodler]

One,you don't need two 1k screen resistors,that will sag quite a bit.What PT are you using?
 That 12AU7 won't drive hard enough that's for sure.
With a 300v PT you likely have more than 360v on the plates.If so,a larger cathode resistor on the EL84's is in order.You are well over maximum plate dissipation.
  When done like the Marshall 18 watt there is almost zero sag,so altering it too much obviously sucks it down.The rectifier is fine.
You definitely need a bypass cap as well.Try a 1000uf-1500uf.They smooth out the buzzy distortion a bit.
  Try a smaller master volume pot value.
Is that 12AY7 paralelled?

[Matty_V]

In its first life this amp was dougs 18w stout, then as my knowledge grew I started messing with it. So the areas I haven't messed with yet are going to be the same as the stout. The PT is the heyboer doug sells.

I'll probably drop in an at7 to see how that sounds in the PI

Should I lower both screen resistors or just use one 1K to run both screens? I'll try a larger cap on Rk, I don't have one that large on hand tho.

I don't have a 500K dual gang pot, I suppose I could run  470Ks across the ends to lower it.

V2 is paralleled, ay7 is whats in there at the moment. Just doing my best to be unconventional.