New ODS Build - Sounding WAY Better!... Little help please?

[heisthl]

That way works but does change the response of the pot slightly, try this:

[odourboy]

That way works but does change the response of the pot slightly, try this:

I never cared for that design. Too much of the signal leaks out of the bottom of the pot and pools in the chassis (unless you do a 'tubes up' build).

[greiswig]

That way works but does change the response of the pot slightly, try this:

I never cared for that design. Too much of the signal leaks out of the bottom of the pot and pools in the chassis (unless you do a 'tubes up' build).

Okay, that's pretty good.

[Structo]

Funny guy

[Structo]

That way works but does change the response of the pot slightly, try this:

Thanks, I did notice when I wired it the way I showed that it was pretty minimal until the last quarter of rotation.
I'll try that way.

[keithrick]

I must be slow today I am not tracking with the last three posts.

It appears that Heisthl has the pot wired as Dumble did, is odourboy joking and I am just not getting it?

[jelle]

Yup!

Jelle

[RJ Guitars]

You have probably gone over your circuits and reflowed things but this solder joint caught my eye.
What size screen resistors are you using on the output?

Like I said, disreguard if you have addressed it.

Thanks Structo... I'm still working through the tweaking process, but things are really sounding good now. I checked out that solder and it all looks good... you can't tell from the picture so much, but it flowed nice.

The screen resistors are 1K ohms and the grid resistors are 1.8 K ohms.

rj

[heisthl]

The screen resistors are 1K ohms and the grid resistors are 1.8 K ohms.

rj

If you're talking grid resistors on the output tubes being 1k8 that's pretty small - 3k3, 4k7 or 5k1 are better values - higher=more clean headroom (to a point). If this is always going to be a 6L6 amp you may want to lower the screens to 500 or 470.

[RJ Guitars]

If you're talking grid resistors on the output tubes being 1k8 that's pretty small - 3k3, 4k7 or 5k1 are better values - higher=more clean headroom (to a point). If this is always going to be a 6L6 amp you may want to lower the screens to 500 or 470.

Thanks you for this info on the grid resistors, I'm still learning a bunch about the fundamentals here. Can I assume that when we are talking about more clean headroom that the impact would be most noticeable on the clean channel?

Also, can you take the info about the screen resistors a bit further technically and talk about what the impact of the 470-500 Ohms would do to tone - stability - or whatever is appropriate? It's likely that I'll always use 6L6's in the final version although it would be great to know and understand the ideal component tweaks for any given tube type.

rj

[heisthl]

The higher output grid resistors aid in not allowing the output tubes to pull current out of the PI. On 12AT7 type PIs you see the 1k5 or 1k8 values but the 12AX7 has less to give and will distort easier with low ouput tube grid resistors. The difference is noticeable even in OD mode.
The screen resistors also affect maximum power output and even though I can't hear the difference between 500 and 1k, I can see it slightly on the scope. I could be hallucinating

[RJ Guitars]

The higher output grid resistors aid in not allowing the output tubes to pull current out of the PI. On 12AT7 type PIs you see the 1k5 or 1k8 values but the 12AX7 has less to give and will distort easier with low ouput tube grid resistors. The difference is noticeable even in OD mode.
The screen resistors also affect maximum power output and even though I can't hear the difference between 500 and 1k, I can see it slightly on the scope. I could be hallucinating

What would happen if we used a 12AT7 for the phase inverter tube? I know that 12AX7's have a gain of 100 and the 12AT7 has a gain of 70, but as a phase inverter will this make a big difference? It's simple enough so I'll give it a try but I figure somebody has already done this and if it was a good idea it would probably be a popular tweak.

rj

[Structo]

Also don't the screen resistors add protection for the power tubes in case one shorts?
Better to burn up a 50 cent resistor than a $100 PT or OT?
The old Princeton Reverbs didn't come stock with screen resistors and I've read that adding them is a popular mod.

[Funkalicousgroove]

I think an AT7 is also a Hi-Mu tube, all the ones I have test as high or better than AX7's on my VTV dual triode characterizer, I think the AT7 produces a larger current gain. If you are looking for smaller amplification maybe try a 5751, 12AU7, 12AY7?

[RJ Guitars]

I think an AT7 is also a Hi-Mu tube, all the ones I have test as high or better than AX7's on my VTV dual triode characterizer, I think the AT7 produces a larger current gain. If you are looking for smaller amplification maybe try a 5751, 12AU7, 12AY7?

If I've got this figured out - "Mu" is tube-speak for gain... let me know if I'm off base here. On the tube data sheets the listed "Mu" is 70 for the 5751 and 60 for the 12AT7. Both of them are referred to as "Hi Mu" although neither of them are as hi Mu as a 12AX7 (Mu=100).

http://www.nj7p.org/Tube4.php?tube=12AT7
http://www.mif.pg.gda.pl/homepages/fran ... 5/5751.pdf

Assume we are in agreement they are both high "Mu and will deliver higher current than a 12AX7 - would that eliminate the potential for the distortion that Heisthl mentions?

The higher output grid resistors aid in not allowing the output tubes to pull current out of the PI. On 12AT7 type PIs you see the 1k5 or 1k8 values but the 12AX7 has less to give and will distort easier with low ouput tube grid resistors.

It may not be worth a lot of discussion, but I'll try it just to learn and see if it's audibly obvious. I say it might not be worth a lot of trouble knowing that it might introduce some other variables that are more significant than the small reduction of distortion.

The only thing driven me is that I'd like to keep the option open to try a set of EL34's without having to change any other components.

rj