Second Dumble #183 build

[erwin_ve]

Anybody notice that the PI plate resistors in #183 look to be 120k and 100k.
CW

Youre one of a kind CW I think youre right!

[talbany]

Anybody notice that the PI plate resistors in #183 look to be 120k and 100k.
CW

I'll be damned
Anybody got a 120K NTE MF resistor I can borrow

Tony

[norburybrook]

so the same as #102 then.


Any one care to hazard a guess as to what effect this might have , technically and sonically?





M

[martin manning]

so the same as #102 then.

Any one care to hazard a guess as to what effect this might have , technically and sonically?

The trimmer will still be used to balance the PI, so the only real difference is an increased plate load on each side (the extra 10k divided in some way), which will increase the PI gain a bit.

[norburybrook]

so the same as #102 then.

Any one care to hazard a guess as to what effect this might have , technically and sonically?

The trimmer will still be used to balance the PI, so the only real difference is an increased plate load on each side (the extra 10k divided in some way), which will increase the PI gain a bit.

LOL like #183 needs more gain

thanks Martin, I presume the #183 layout and schematic need changing then and everyone will be out swapping resistors i sold mine i don't think the new owner will be any the wiser though.


M

[talbany]

so the same as #102 then.


Any one care to hazard a guess as to what effect this might have , technically and sonically?





M

Actually, 183 is different than any other PI I've run across (or noticed). Dumble always uses 110/120k or a 100k/110k pair (other than the 2nd gen's). He usually keeps them within 10k from each other. This one is 20k. I wonder why?. I doubt you will really be able to tell much difference unless you really crank the amp and drive the PI hard. It would be an interesting A/B test to see how it affects PI headroom if at all
BTW. He also uses higher value grid feeders on this amp as well?

Tony

[norburybrook]

so the same as #102 then.


Any one care to hazard a guess as to what effect this might have , technically and sonically?





M

Actually, 183 is different than any other PI I've run across (or noticed). Dumble always uses 110/120k or a 100k/110k pair (other than the 2nd gen's). He usually keeps them within 10k from each other. This one is 20k. I wonder why?. I doubt you will really be able to tell much difference unless you really crank the amp and drive the PI hard. It would be an interesting A/B test to see how it affects PI headroom if at all
BTW. He also uses higher value grid feeders on this amp as well?

Tony

Ah, so it's 100/120? I presumed 110/120

If I still had my amp I'd definitely change it

it's not a good enough reason to build another though

M

[Oddvar R]

I always get a problem with the .015uF capacitor. Is there any reason why it is 1200v? And is it important? Alternatively: Is there a place to get them?

183ver11 (7).jpg

[norburybrook]

I always get a problem with the .015uF capacitor. Is there any reason why it is 1200v? And is it important? Alternatively: Is there a place to get them?183ver11 (7).jpg

I'd say it's because that's all he had in his box of that value. It doesn't need to be 1200v

have you tried Mouser?



M

[Oddvar R]

I have it in 600v, but I wondered if 1200 was of some significance. Thanks.

[talbany]

I have it in 600v, but I wondered if 1200 was of some significance. Thanks.

IMO The 1200 volt caps do have a different sound than the 600's (it's also a 715). Did Dumble pick that cap because of the sound? I don't know ask Dumble. Did Dumble just stick that one in because it's the only one he had in his drawer? I seriously doubt it. Again I am not Dumble

Tony

[hitchcaster]

yeah, the different voltages sound different. you just have to try, theres no rule.

[Oddvar R]

Any idea where to get them?

[sluckey]

here...

https://www.mouser.com/ProductDetail/Co ... ioZgWKg%3D

[Oddvar R]

Oh thanks, that's great.

Another question: Is the fet amp really necessary for the build? And if it is, why?