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Old 19th December 2004, 06:49 PM   #21
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I don't have many values on hand but I found that this one got rid of the problem of the voltage ramping up and down on the output. It looked like a strange oscolation(sp). When I disconnected it the problem went away so I assumed it sure wouldn't hurt to try a different value. When I tried the 27K it acted correctly without a ramping problem and still gave me the same output. just running the output to the scope I get 29V rms out with 3 volts in, the same as before.

I made a twisted wire pair from 1" of #22ga wire and twisted the two together and soldered one end of each and floated the other end. Is this correct to replace the cap in the feedback loop?

Sound ...

Its ballsey with a lot of punch.
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Old 19th December 2004, 07:00 PM   #22
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Yeah, that 'cap' seems OK. It was a standard practise in the hf world long time ago, don't know if they still use it.
I thought that the change of R102 to 27k would *increase* the problem, as it give stronger bootstrapping to the input, which is a form of pos feedback. But there probably was some phase shift through that 330pF turning it back into neg feedback. Funny how complex simple circuits can be...

Glad you enjoy the sound - that's the final arbiter, isn't it.

Jan Didden
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Old 19th December 2004, 08:47 PM   #23
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Without the 330pf cap there I still had the same problem. No matter what I did it kept ramping DC on the output. I'm still not satisfied with what I did. Is there a better solution?
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Old 19th December 2004, 10:38 PM   #24
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Is that "ramping" an up and down drift of the DC with a period on the order of a second or two?
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Old 20th December 2004, 02:12 AM   #25
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The ramping process takes more on the order of about 10 seconds. I am wondering if it would be of benefit to change the 470K R110 value to 100K?
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Old 20th December 2004, 02:34 AM   #26
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Default JURASSIC PORK?..........

Hi,

Quote:
I am wondering if it would be of benefit to change the 470K R110 value to 100K?
It would speed up discharging the cap, yes.
As a side effect you may get somewhat better dynamics as well...

Where the heck does that dinosaur of a circuit come from anyway???
Geeeezzz.........

360V on that CF's plate seems rather steep too....
If you'd use a split cap configuration on the output you could at least do away with the input cap (C110).
That should improve the sound.

I think Jadis reworked the thing later on to use a lower B+, a 12AU7 CF as the first triode followed by a 12AX7 direct coupled to a 12AU7 CF.
Still needlessly complicated IMHO.
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Old 20th December 2004, 02:59 AM   #27
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Hi Frank

Can you point me towards a link for the Jadis schematic?


Quote:
Where the heck does that dinosaur of a circuit come from anyway???
Geeeezzz.........

Leave it to me to drag in something completely out of date.
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Old 20th December 2004, 03:32 AM   #28
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Hi,

Quote:
Can you point me towards a link for the Jadis schematic?
Not sure where it was I found it...
Probably one of those Asian sites I guess...
Not even sure it's an actual Jadis circuit.
It did say so where I had it from but I'm starting to doubt these folks' sanity lately...(I'll leave it up to a guess as to whom I'm refering to......)

I took the liberty to add some comments.
No idea what it sounds like, you'll probably be running it with the handbrake firmly in the up position given the gain of the thing........

Cheers,
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Old 20th December 2004, 08:54 PM   #29
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I changed the R102 value back to 470K. I changed the R110 value from 470K to 100K. I now acts normal and the DC offset stays in the 40-50mv range.

With the grounding at one point on the circuit board I still have hummmm.

Any ideas?
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Old 20th December 2004, 08:59 PM   #30
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Hum in both channels?

Hum with inputs disconnected?

Hum that stays the same in level when tubes are swapped around?
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