Can I remove the input caps?

Nightpuma · 4th April 2006, 12:13 PM

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.

SY · 4th April 2006, 12:19 PM

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.

Nightpuma · 4th April 2006, 11:59 PM

Hi.

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

Theo

Svein_B · 5th April 2006, 06:27 AM

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.

rdf · 5th April 2006, 07:31 AM

As drawn I think C14, by removing any DC grid reference to ground, will temporarily turn the tube into a nightlight. But only temporarily.

Nightpuma · 5th April 2006, 05:27 PM

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

rdf · 6th April 2006, 02:55 AM

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?

Svein_B · 6th April 2006, 07:01 AM

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.

Svein.

Nightpuma · 11th April 2006, 02:35 PM

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

Nightpuma · 11th April 2006, 04:29 PM

Hi

I got it figured out. Cornell Dublier PIO caps.

Theo

4th April 2006, 12:19 PM	#2
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	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. __________________ "...we stumble and get up, we are sad, confident, insecure, feel loneliness and joy and love. There is nothing more; but I want nothing more.” - Christopher Hitchens 1949-2011

5th April 2006, 07:31 AM	#5
rdf diyAudio Member Join Date: Jun 2004 Location: the thermionic past	As drawn I think C14, by removing any DC grid reference to ground, will temporarily turn the tube into a nightlight. But only temporarily. __________________ Blame the Manichaeists

6th April 2006, 02:55 AM	#7
rdf diyAudio Member Join Date: Jun 2004 Location: the thermionic past	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? __________________ Blame the Manichaeists

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4th April 2006, 11:59 PM	#3
Nightpuma diyAudio Member Join Date: Apr 2006 Location: copenhagen	Hi. I understand. I'll draw a complete circut diagram and return. Theo

5th April 2006, 06:27 AM	#4
Svein_B diyAudio Member Join Date: Oct 2005	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.

5th April 2006, 05:27 PM	#6
Nightpuma diyAudio Member Join Date: Apr 2006 Location: copenhagen	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

6th April 2006, 07:01 AM	#8
Svein_B diyAudio Member Join Date: Oct 2005	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. Svein.

11th April 2006, 02:35 PM	#9
Nightpuma diyAudio Member Join Date: Apr 2006 Location: copenhagen	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

11th April 2006, 04:29 PM	#10
Nightpuma diyAudio Member Join Date: Apr 2006 Location: copenhagen	Hi I got it figured out. Cornell Dublier PIO caps. Theo

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