5687 line amp with 0D3 regulator - diyAudio
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Old 6th August 2003, 04:14 AM   #1
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Default 5687 line amp with 0D3 regulator

Well, its up and running. The first tube sounded like crap and was microphonic. I can only assume that it was bad to the bone. I replaced it with another Tung Sol and its sounding and running mighty fine. I will have to admit that it is the best sounding line amp I have heard yet. I settled for a plate voltage of 135volts and cathode voltage of 5.0 volts. With the 470 ohm cathode resistors I make this out to be about 10.6 mA per section. I assume it is within safe operation for the tube.

Frank

I haven't been able to download a grid sheet on the tube so maybe someone could send me one thru email. Frank I think regulation helps with the sound. It sounds better with the 0D3 than it does unregulated.
I didn't think the chokes made it sound unnatural either.

Joe
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Old 6th August 2003, 05:00 AM   #2
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So you got a schematic for it yet?
BTW a good rule of thumb is to have maybe half the supply voltage across the plate resistor, and the other half across the tube (Vp=75V in your case). If it's heavily loaded (Rl = 1 or 2 * plate load R), as low as Vp = 1/3 B+ may be necessary for low distortion. But it all depends on your requirements.

Glad you like it.

Tim
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Old 6th August 2003, 10:00 AM   #3
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Hi,

Quote:
I haven't been able to download a grid sheet on the tube so maybe someone could send me one thru email.
It's on its way already.

Quote:
It sounds better with the 0D3 than it does unregulated.
No surprise to me but you can only be sure if you compare the two under the same working conditions...
Was that the case?

By the way, are you using one OD3 per channel or is it common to both?

Cheers,
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Old 6th August 2003, 12:09 PM   #4
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I'll try to send a schematic
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Old 6th August 2003, 12:25 PM   #5
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I'm using a 2K grid resistor and ending up with 135v on the plate.
The 0D3 is providing the regulation to both channels. I am considering using a 0D3 per channel. I tried using a voltage dropping resistor before the 0D3 but that wouldn't let the 0D3 fire up. The power supply consists of a Hammond 272BX transformer, a 6X4 rectifier tube, a 30H choke followed by a 50mfd cap to ground followed by another 30H choke and another cap to ground. The 0D3 goes from B+ to ground and the grid resistors attach to pin 5 of the 0D3.

Now, if someone can tell me what I am doing wrong here it would be appreciated. The problem seems to be that I cannot get the 0D3 to stay lit with the correct load dropping resistor. I can get it to work by using the load provided by the plate resistors and the tube draw.
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Old 6th August 2003, 12:37 PM   #6
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Frank

Thanks for the info.

I listened to the line amp with the 0D3 out of circuit and the appropriate plate resistor to achieve the same plate voltage as with the 0D3. It sounds more dynamic with the 0D3.

Joe
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Old 6th August 2003, 09:56 PM   #7
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Yikes!! For one thing the most capacitance across a reg tube should be .1uF -- you have 50! I guess the only thing keeping it from oscillating is the extreme current going through it, which should roast the 6X4 pretty quickly too.

Tim
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Old 6th August 2003, 10:06 PM   #8
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Hi,

Quote:
Yikes!! For one thing the most capacitance across a reg tube should be .1uF -- you have 50!
Where? I don't see any cap across it.

Quote:
I guess the only thing keeping it from oscillating is the extreme current going through it, which should roast the 6X4 pretty quickly too.
What extreme current? The 6X4 is good for 70 mA with an LCL filter, so ?

If you want something to chew on, this could make you happy.

Cheers,
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Old 6th August 2003, 10:08 PM   #9
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I didn't see any resistors on the bitmap he attached.

Here's a circuit. HTH.

Tim
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Old 6th August 2003, 10:21 PM   #10
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Joe,

Replace the 3k with a CCS set for 28mA. A DN2540 or an IRF820 would do.
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