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Scott299 high mids and low tweets distort.


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On 4/9/2004 9:25:00 PM Ryan C. Inman wrote:

The three lights on the front panel are NE-2 neon bulbs, they run off of the high voltage power supply. If they are more dim than they once were, or if they blink, that is an indicator of filter capacitor failure. Defective filter capacitors will load down the power supply, causing the voltage source for the neon bulbs to drop (they become dim or won't fire).

NE-2 bulb failure is rare, and when I see one go dim, it is generally a power supply problem. They can fail (if the amplifier was used a lot in the past), but they generally last a very long time. I'd check the power supply capacitors, especially the 20-20-25-25 uF 450V can capacitor for leakage.

-Ryan

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Hmmmm interesting 2 bulbs with the same power source one bright/normal the other dim. Seems like your barking up the wrong tree to me. But pretty much a useless point since tube rolling and connection checking solved the problem anyway.

Craig
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Hi Wrench_peddler,

I'm glad you got that there amp up and running with no distortion. That there amp you got is the one you got from me (I got it from edster00). Is that gol dang hum buzz still there? I heard from Craig that swapping out the transformers didn't do the trick. Did you ever find the trick? Glad to hear that the Scott amp is winning some bake-offs down there. I'm sorry that amp is so notorious!

Strangely enough, I too had distortion problems with my Scott recently. After futzing around with an oscilloscope for the better part of several evenings I sent it to Craig and he had it fixed in about 20 seconds! The culprit was a bad pin socket for pin 1 of the 12AX7.

Later,

Mace

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Hey Mace, I moved the amp to a different room a couple of weeks ago and the hum is about half of what it was before. Still don't have a clue. One thing I noticed about the lights today when I fired the 299 up, was that both lights came on with the same intensity for about 1 second until the protector circuit or what ever it is that switches the speakers on switched. The left light suddenly dropped to about half intensity. Sound is fine but that light has to be an indicator of something funny going on. I still haven't found my volt meter but as soon as I do, I will give it a good look see.

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Steve,

The only thing that the lights are telling you is that one of the neon bulbs is weak. All the lights are fed by a common tap from the 225V tap on the power supply thru a 150kohm resistor and the selector switch. Each lamp has it's own 680k resistor in series which also may be changing as it heats up. But none of this is affecting your other problem.

Maybe a different brand of coupling cap would tone down the highs. Could be one of them is leaking, who knows. Just because something is new doesn't mean that it is good. Did you ever tune up a car with points and condenser and have it not start afterwards? Put in the "old" condenser and VAROOM!? That happened to me more times than I can count back in the day. Condenser, capacitor, same, same.

Here is the schematic:

http://hhscott.com/pdf/sd/299B_3_4s.JPG

(Edit:

http://hhscott.com/pdf/sd/299A_3_4s.JPG

The light circuit is the same.)

Rick

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Rick,

Read the entire thread the problem is gone already. No cap change required. I personally think the buzz issue that (keeps being discribed with hum which has no hum element at all, Hum comes from the woofer guys not the mid or tweeter) is just a by product of the 299A first edition poor wiring layout or ? I think Scott redesigned this amp for a reason !

Also that is not the schematic for the 299A first edition. The link is to the 299B

Craig

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happy Deano !

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On 4/11/2004 6:06:53 PM Ryan C. Inman wrote:

nothing can make a 299 or 299-B sound good
11.gif

--Ryan--

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You haven't been to my house.2.gif Those who have will tell you differently. I'm not just tooting my own horn or Craig's.

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