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Old 4th April 2006, 12:13 PM   #1
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Default Can I remove the input caps?

Hi.

I don't have much experience fiddling with electronics, so I need a little advice her.

I have a Graaf GM 13.B preamp which I have decided to try to sing more beautiful. Taking one thing at a time, I have decided to change the output caps. The amp also have 0.18 uF input caps to block DC I suppose. Do you think it would be wise to remove these?
It's a balanced design.

I've made a drawing of the beginning of the circut.
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Old 4th April 2006, 12:19 PM   #2
SY is offline SY  United States
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The drawing makes very little sense. You need to trace this out much more thoroughly.

If you don't have a schematic and don't have a clear idea of what you're doing, the question is not whether or not you'll get smoke, but how much and how badly.
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Old 4th April 2006, 11:59 PM   #3
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Hi.

I understand. I'll draw a complete circut diagram and return.

Theo
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Old 5th April 2006, 06:27 AM   #4
Svein_B is offline Svein_B  Norway
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I think the input of this amp is a diferential/LTP stage.
Measure the voltage at the grid, and I think you will find that it is not at ground level.

If my understading is right, the caps must stay.

Svein.
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Old 5th April 2006, 07:31 AM   #5
rdf is offline rdf  Canada
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As drawn I think C14, by removing any DC grid reference to ground, will temporarily turn the tube into a nightlight. But only temporarily.
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Old 5th April 2006, 05:27 PM   #6
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Hi.

Thanx alot. The cap stays.

But what about changing the value down to .15 uF or up to .22 uF? Easier to find good cap.


Theo
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Old 6th April 2006, 02:55 AM   #7
rdf is offline rdf  Canada
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Sorry, I should have been more specific. I don't understand what keeps that tube from burning up with C14 left in the circuit. Unless it's something completely new to me (not that big a challenge) C14 prevents will cause the grid to float positive and make bad things happen. There is no external DC path between grid and cathode as drawn. Are you sure about that schematic?
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Old 6th April 2006, 07:01 AM   #8
Svein_B is offline Svein_B  Norway
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I think the confusion regarding C14 is because some important parts are not shown.

If we imagine a voltage divider between plate or b+ and ground to feed the top of c14, we establish a grid reference voltage, presumably somewhere in the range 50-100V, for the tube.
If we further assume that the tube shown is 1/2 of a differential LTP, we have established some "space" for a common cathode resistor.

This is just my assumptions from looking at a similar amp a few days ago.

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Old 11th April 2006, 02:35 PM   #9
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Hi.

Thanx for helping me out. Found out that I needed some more teoretical understanding, so I've started reading

But, can any of you identify the caps?

http://www.hifisentralen.no/album/Ni...SCN0533_rs.jpg

Brand and type?

Theo
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Old 11th April 2006, 04:29 PM   #10
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Hi

I got it figured out. Cornell Dublier PIO caps.

Theo
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