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Old 4th April 2006, 05:51 PM   #11
bibster is offline bibster  France
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This is not even to be considered at all...

I'm prototyping this thing, and for now it seems to work, so I'll start making it work *properly*!
Putting components in the right spot, and connecting them properly is one of the main things in that.
I'll replace the 22K resistors, as they're like burned by now.... I've put some 6k8 before, and ended up having 88.3 and 92.3 volt on the plates... that's allready a lot better.
I'll try schiller's hint: These R's and c's are supposed to be between the NiCd's and the cathode, right?
There's too much hum from the PS, so I'll fiddle with that a bit, and once it works *properly*, I'll just redo the whole thing !

Thanks,
Paul
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Old 4th April 2006, 07:07 PM   #12
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Hi Paul,
For your lack of bass try a larger output coupling cap. Something around 1-1.5uf

Andy
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Old 6th April 2006, 04:26 PM   #13
kevinkr is offline kevinkr  United States
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You use either the nicads or the resistor capacitor combination, not both.

I was a big advocate of bias battery in the cathode circuit, but have come to the conclusion that it doesn't always sound even as good as conventional cathode bias with a cap and resistor. To some extent this seems to depend on the quality of the battery involved and whether or not the battery voltage allows you to achieve the desired operating point.

In my experience fixed bias applied to the grid often ends up sounding better, but requires a coupling cap between the grid and whatever is driving it. (This seems particularly true in stages required to deliver significant signal current such as the output stage in an otl headphone amplifier.)
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Old 6th April 2006, 06:39 PM   #14
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I agree with Kevin. It very much depends on the type of battery used. The newer batteries tend not to sound very good.
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Old 7th April 2006, 11:35 AM   #15
bibster is offline bibster  France
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Well,

They're new, these NiCd's, samsung, and deliver 2.78V.
I don't know if this is 'enough' to get me to the desired operating point, simply because I don't know what this desired, or optimal, operating point is for a typical 5687.

The soundstage is, at he moment, very flat: My wife said it lacks 'depth' ('Ca manque du profondeur'). As I've said before, I suspect a lack of bass, so, (thank you Andy for your hint) I'll try:

1st: 1 or 1.5 uF output caps,
2nd: R+C bias on the cathode.

I could then try to use the 0.47uF exit form the output on the input, and make a fixed bias for the grid (Could you give me a hint how to achive this, Kevinkr?)

Won't be doing that this weekend, but I'll try to measure the linestage a bit with my Edirol UA-25 + rightmark software (Any other hints for measuring? osX or WinXP)

Thanks!

Paul
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Old 11th April 2006, 11:29 AM   #16
bibster is offline bibster  France
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Default hummmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm

Hi,

I've been fiddling with this thing for a while now, and I suppose my house is now filled with Bees.... Or at least: that's what is sounds like!!

I've taken out the NiCd's, replaced them with a 500Ohm multitour pot. // 2200uF Electrolytic. (one for each pair of cathodes, one per tube thus) as Schiller suggested.
Replaced the plate resistors by one 22K/5W per tube.
Adjusted the pot. to achive 220V over the 22k (10mA) per tube. (Something like 105 V on the plates)
Is this the right way to go?

Anyhow, as I said: humming all over the place this thing: Measured with RMAA, I've found 50Hz (Europe!) at -60dB, 100Hz at -64dB AND SO ON untill the end of the spectrum.

Hmm.. I think: Some pb. in the PS: Electrolytic broken or so thus not filtering very well.. (How can I figure this out? Haven't got access to a scope...)

But then, when I turn the amp off, by means of a SPST switch in the primary circuit of the tranny, this hum STAYS....

When the PS is completely discharged, and I keep watching the spectrometer, the hum is still present...

But when I unplug the powercord... you get it.

TEMPORARILY diconnecting the Earth from the mains doesn't affect the problem... Even though I've found 0.3v between N and EARTH in the outlet....

Any hints, as to help me finding the source?

Kind regrads, Paul
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Old 11th April 2006, 11:35 AM   #17
SY is offline SY  United States
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Photos will help. 50 Hz probably means that you've got inductive pickup somewhere, from transformer radiation or lead dress.
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Old 11th April 2006, 10:04 PM   #18
bibster is offline bibster  France
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Okay,

Implemented some new (at least for me... dummy ) grounding scheme, and got the hum some 20dB's down.. Good
Now for the bad (Or again: odd) Inputs are shielded wires (Shield unused, not connected) to a 6x2 switch, then 2 inches of unshielded to the Alps bluepot, then again shielded (Shield still unused, not connected) to the 100R grid resistors.
Now: When I get my finger NEAR the LAST bit of wire (Pot to grid resistor) I get some heavy hum, like when you touch an unconnected input.
When I get near the other bits, no hum at all.....
And: When the pot in at NILL or at FULL, the effect in zero. in the the effect is largest...

How come? (Izzit the low input impedance of the grid or so???) and, far more interesting: What to do to eliminate this (so far) last bit of hum in my linestage?
(I think it picks up the 50Hz+harmonics VIA this bit)


Goodnight, Paul
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Old 11th April 2006, 10:16 PM   #19
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ehm... use 1k grid resistor...something to do with miller.....
-pls correct if i'm wrong-

or: don't put your finger inside the lady....
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Old 12th April 2006, 07:20 AM   #20
bibster is offline bibster  France
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Quote:
Originally posted by kathodyne
something to do with miller.....
or: don't put your finger inside the lady....
100Ohm/15 (at about) is indeed quite low, thus eager to pick up hum (??)
I see... I'll try some higher grid resistors...

The thing is however (Refering to your 'putting fingers in things') is that the 'last bit of wire' picks up ANY hum
(Tige dank foar dyn hint, however!)

Paul
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