6V6grid stooppers and other questions

[daz]

I was afraid if i started messing with tube amps again i'd over run this forum again and here we are with the 3 latest posts by me ! Sorry ! Anyways, i'm wondering exactly why some 6V6 amps have grid stoppers and others don't. Are they there to eliminate possible oscillations? I bypassed the 5.6k's i have on mine and don't notice anything so i wonder if i would hear or FEEL a difference at loud volumes. Any thoughts? Also, what do you think about filter size on the output? This amp was formerly el34 but i changed it to 6V6 so i wonder if the 50/50uf can might be why the amp is a bit stiff feeling. I see other 6V6 amps using 32 or even 16uf.

[Helmholtz]

Are they there to eliminate possible oscillations.

Yes, meaning RF oscillation, which is not really predictable.

Regarding filter caps I prefer lower values with lower power amps.

[daz]

Makes me wonder then....why do some not use any grid stoppers? If they don't change the tone of feel who not? Or DO they change anything? Like i said i didn't notice but then again i can't turn it up very loud here.

[Helmholtz]

Makes me wonder then....why do some not use any grid stoppers? If they don't change the tone of feel who not? Or DO they change anything? Like i said i didn't notice but then again i can't turn it up very loud here.

As long as the amp doesn't oscillate, you typically don't hear a difference.
But it might oscillate with different lead dress, layout, tubes, OT, speaker and sometimes even with different controls' setting.

Grid stoppers can help but are not always enough to prevent oscillation.

RF oscillation itself is not audible but can produce nasty distortion artefacts.

[daz]

The lead dress in this amp is horrific because it's been a test mule of mine for years ! It's a slop fest. But it sounds great and tho i am only able to turn it up for a few seconds here and there i don't notice any oscillations. But i did take a que from you and threw a 32/32 JJ can in it in place if the 50/50 F&T just now and it does seem like the attack is a bit less stiff, so thanks for that.

[Helmholtz]

A neat lead dress/layout isn't necessarily superior .

Esthetics is not a category of physics.

[daz]

A neat lead dress/layout isn't necessarily superior .

True, but this thing is a slop fest way beyond just wire routing. But funny thing is, i used to build a amp then tweak and re tweak it for endless hours over the course of months till it was the same degree of slop as this one, then once i got it where i liked it i would order a new turret board and most of the components and even pots and sockets if it was bad enough. Then i'd rebuild it nice and clean and new to the same circuit i finalized and ya know what....i did this no less than 4 times and not once did the new clean amp sound better. Sometimes not quite as good ! So i stopped doing that and this one will stay as is even if it becomes my main amp. The only thing i'm doing is making sure the worse of the solder joints are solid. Hours of work there. Some wires are just piled on top of each other in a giant solder blob. It's really quite comical, but as i said tone wise it makes no difference. Even lead dress is all over the place but if it sounds good it sounds good. My only job now ill be making it reliable.

[g1]

Lack of power tube grid stoppers is more likely to be found in older designs (or clones of them).
Maybe old tubes were tighter spec., maybe less simple amp designs were more prone to oscillation, not really sure why they became more the norm.
Generally, adding them where they are missing is considered an upgrade/update, and within reasonable limits there shouldn't be an audible difference.

[Chuck H]

re: lead dress and grid stops...

If your amp is a spaghetti monster that doesn't at all mean there's any problem with instability. In fact the opposite could be true, IF, by chance, any interaction between radiating fields is of opposing phase. This could have a stabilizing affect. In truth your amp may have both detrimental and corrective interactions happening at the same time and the result, for this build, is stability. I would HIGHLY recommend that you be very careful to not change anything about the lead dress in an attempt to "improve" it because at this point it could have the opposite result. Part of YOUR amps mojo now hides in the little interactions happening due to your lead dress and you could lose some of that invisible magic if you change anything. Of course it's not magic. And all things can be measured. But what and where to measure??? WRT lead dress this can be difficult and if lead dress is convoluted it gets even harder. So my suggestion is don't change it without paying close attention how you can change it back.

All the above info on grid stops is good. But put them back in anyway. If you're not hearing a difference then they aren't hurting anything by being there. Grid stops on power tubes started to be employed more frequently as guitar amps started be used at (and subsequently designed for) higher gain. You don't need to discover that at some point there is instability because you changed a setting on a boost pedal or tried something new otherwise. It's really only the oldest vintage designs that are not high gain (by guitar amp standards) that omit grid stops and those amps were absolutely not ever expected to be played at distorting levels intentionally. If the designers ever thought that a player might wish to turn them up to clipping levels they probably would have added grid stops as a precaution.

JM2C

[daz]

re: lead dress and grid stops...

If your amp is a spaghetti monster that doesn't at all mean there's any problem with instability. In fact the opposite could be true, IF, by chance, any interaction between radiating fields is of opposing phase. This could have a stabilizing affect. In truth your amp may have both detrimental and corrective interactions happening at the same time and the result, for this build, is stability. I would HIGHLY recommend that you be very careful to not change anything about the lead dress in an attempt to "improve" it because at this point it could have the opposite result. Part of YOUR amps mojo now hides in the little interactions happening due to your lead dress and you could lose some of that invisible magic if you change anything. Of course it's not magic. And all things can be measured. But what and where to measure??? WRT lead dress this can be difficult and if lead dress is convoluted it gets even harder. So my suggestion is don't change it without paying close attention how you can change it back.

All the above info on grid stops is good. But put them back in anyway. If you're not hearing a difference then they aren't hurting anything by being there. Grid stops on power tubes started to be employed more frequently as guitar amps started be used at (and subsequently designed for) higher gain. You don't need to discover that at some point there is instability because you changed a setting on a boost pedal or tried something new otherwise. It's really only the oldest vintage designs that are not high gain (by guitar amp standards) that omit grid stops and those amps were absolutely not ever expected to be played at distorting levels intentionally. If the designers ever thought that a player might wish to turn them up to clipping levels they probably would have added grid stops as a precaution.

JM2C

U think a lot like me. Common sense stuff. The grid stopper bypass wires i removed soon as i realized there was no difference i could hear, and the lead dress i wouldn't think of messing with when the amp sounds good. If there were noise issues i might but why fix what ain't broke.... will almost surely break it because theres only one direction you can go from perfect.

[Chuck H]

... will almost surely break it because theres only one direction you can go from perfect.

Well I've been here a while and I remember how you struggled to get to THIS amp. And how much time and trouble you spent tweaking it. So I only offer my best advice to NOT undo it

[daz]

But the truth is my tastes have changed and had i came to this exact design a ways back i probably would have changed it from where it is now. I'm more after that lower gain classic rock sound ala petty, beatles, stones rather than bad co, skynard, zep etc. Tho i want to still be able to get that too at least to some extent. Think tom campbell with the ability to do higher gain rock too when needed. But i want it's forte to be the latter. And when i said perfect i didn't mean the tone is perfect, i was referring to the fact there are no noise issues requiring i mess with lead dress. I still may try some other things like shite canning the CF and feeding the tone stack from the last gain stage to eliminate the marshall CF sound. Just something i'm considering because i've done that b4 and liked it and i wanna get away from the marshall thing to some extent. But thats just a thought at the moment.

[daz]

After posting the above i remembered i can drive the tone stack from the third stage bypassing the CF just by removing and swapping a couple wires so i tried it. Sounded great. I think i may leave it or even put it on a switch and have both options. Man, this is what i feared when i dusted off this old build and started using it instead of modelers. I really don't wanna get back into this never ending tweak fest that i tend to fall into. Luckily at this point i'm too old to have the energy to take it too far.....hopefully.

[Chuck H]

Need two likes here. So here you go

[Chuck H]

The truth is that all the vintage stuff was designed to deliver a good clean tone all the way up to full power. Which means that if it went a little beyond that it had to be done gracefully. That's one reason all the old amps do that edge of distortion "tweener" sound so well. And this is really the thing you need for most vintage tones. If you can clip a little gracefully then a good boost pedal or dirt box can take you the rest of the way. The opportunity for a good clean tone is already implied in these amps. And...

This is a concept I've always struggled with. The best players aren't typically using high gain amp channels, but rather the normal or clean channels set up to just hint at distortion and then their own pedal chain. Pretty much just as it's always been even with the vintage amps. So just what IS a good tube amp? I'm starting to think it's an amp that will make a good clean tone to full power and clip gracefully to a point as it goes into distortion. And really nothing more. Though...

There are many coveted sounds of heavily clipped amps. This is where my forte in amp design has been for a long while. Though I do spend some time in the preamp clipping area too. Still, I think the most important thing a "good" tube amp can do is make a good clean tone nice and loud and IF it clips, do it gracefully from that point and a bit forward. If the amp does that then I think most most good players would be able to make music with it. And that's the point really.