Resistor value question

[pbman1953]

I'm installing new caps in a Sunn 2000s, please see web page to the map below. The last stage of the filter caps is asking for a 30k resistor. Locally I can find a 33k or I can  connect in 2 in series to add to 30k. Would the 33k be that much off of 30k?

Thanks

http://www.freeinfosociety.com/electronics/schematics/audio/sunn2000s.pdf

[tubenit]

Maybe I am reading this wrong, but I am seeing a 33k not a 30k in that last dropping resistor in B+ to the last filter cap?

And I personally wouldn't hesitate to try a 33k for a 30k anyway.

With respect, Tubenit

[pbman1953]

You're 100% right. It's a 33k. Ok , new question, what if the store only has values either side of 33.

[sluckey]

But you said "Locally I can find a 33k".

[pbman1953]

Wow I'm really putting my foot in my mouth right?. They'll have a 30 not 33.  The question I guess it's if they don't have the 33  what is the closest I'd be allowed to sub

[sluckey]

In that position I would use anything from 10K to 47K, but really, 33K is a very common value. Try to get as close to 33K as you can.

[Willabe]

V2 6AN8, B and C nodes go to its plate. Is that a misprint?


                Brad    

[sluckey]

Node B only feeds the triode plate. Node C only feeds the pentode plate.

[Willabe]

Node C goes to a 270K plate R going to pin 6. Node B goes to the triode 47K plate R pin 1 and a 12pF cap going to pin 6 and pin 2 (grid) of triode.


               Brad      

[sluckey]

and a 12pF cap

That's right, but that ain't the same as going to the plate. Think of node B as an AC ground. That 12pF cap simply goes from the plate to ground. A smoothing cap or hi freq snubber.

I never liked the way that circuit was drawn. Does this look more logical?

http://home.comcast.net/~seluckey/amps/sunn/sunn_sceptre_1971.pdf

[Willabe]

I never liked the way that circuit was drawn. Does this look more logical?

Yes.

That's right, but that ain't the same as going to the plate. Think of node B as an AC ground. That 12pF cap simply goes from the plate to ground. A smoothing cap or hi freq snubber.

So they run it to the B node so as not to lose any of the dcv grid bias instead of going to ground?

Why didn't they just run it across the 270K plate R, node C?


                   Brad      

[sluckey]

So they run it to the B node so as not to lose any of the dcv grid bias instead of going to ground?

Makes no difference whether the cap connects to node B, or node C, or chassis ground. No effect on the dc voltage on the grid.

Why didn't they just run it across the 270K plate R, node C?

Engineers. Go figure!  

Here's my theory. Remember, Sunn copied that circuit from the Dynaco Mark III. I think that cap was added after the proto Dynaco was built. Maybe there was some hi freq oscillation happening and the Dynaco engineers snubbed it out by putting that 12pF from the PI grid to ground (actually node B, since node B feeds the PI triode.

In the Sunn, that cap is physically connected directly to pin 2 (grid). Maybe it is more effective being mounted right on the grid pin (kinda like a grid stopper). Just guessing. Anyway, 12pF ain't gonna change the sound of a guitar signal, so I suspect the purpose was to kill some higher frequency nuisance signal. This is all just my opinion and I could probably easily be persuaded to think otherwise.  

Here's a pic of that cap in a Sunn chassis. I wonder how Dynaco actually mounted the cap.

[Willabe]

No effect on the dc voltage on the grid.

   Still a cap, so it won't pass dcv.

Engineers. Go figure! 

In the Sunn, that cap is physically connected directly to pin 2 (grid). Maybe it is more effective being mounted right on the grid pin (kinda like a grid stopper). Just guessing. Anyway, 12pF ain't gonna change the sound of a guitar signal, so I suspect the purpose was to kill some higher frequency nuisance signal.

Ok, makes sense.


               Brad      

[sluckey]

Still a cap, so it won't pass dcv.

OK, that's true. I just don't understand your point?

[Willabe]

Still a cap, so it won't pass dcv.

OK, that's true. I just don't understand your point?

I was thinking wrong. Forgot about that it's a cap and won't pass the dc. I was thinking of it as an R to ground. 


              Brad     

[pbman1953]

Thanks guys, I'm off to the store