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Old 6th April 2003, 12:42 PM   #21
SHiFTY is offline SHiFTY  New Zealand
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I guess thats the fun part? Adjust it till you find the "sweet spot"!
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Old 6th April 2003, 01:24 PM   #22
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Wouldn't you end up with a slightly cleaner (distortion) signal running it harder? Probably nothing that you would hear but could measure on a distortion analyzer.

Your project looks like what I have been searching for. I wanted to find a simple KT 88 SE amplifier I could use in my study. I would like to go lower in frequency to say at least 20HZ or lower.
Any recommendations for the transformer primary impedance? I would like to price a bargan basement transformer like a Hammond and if I like the sound go to a good piece of iron. Since I am new to tube transformers and I am uninformed please include part numbers and manufacturers.

uninformed Joe
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Old 6th April 2003, 01:32 PM   #23
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My guess is that a Hammond 1628SE will work just as well as mine. (Well, hopefully mine will sound a little bit better considering the money I've spent on it )

I've had the amp running for about 4 or 5 hours on my kitchen table, and I must say I'm suprised at how wonderful it sounds. Allthough a few more watts of outputpower wouldn't hurt I don't think it's worth the extra work right now. Who knows.... Maybe in the future I'll redesign the input stage and get more power.
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Old 6th April 2003, 02:17 PM   #24
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Mikael

Thanks for the reply. I'm sure that you amp sounds great especially with the good iron. I just wanted to play with a bare bones version before I commit to some high dollar iron. What kind of power supply do you have? I may have missed it if you posted it. Did you go with tube rectifier or SS diodes? If you haven't posted it would you mind doing so? What do you figure the power output is ?

Sorry about the 200 questions here but being uninformed as I am I need to ask.

uninformed Joe
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Old 6th April 2003, 02:31 PM   #25
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I use a SS rectifier. I have one big 2200uF lytic cap bypassed with one smaller 47uF lytic cap and one 4,7uF polypropylene. This will probably change a little when I build the final version with my mains-transformer. Right now I use a variac with a cheap transformer I found that was intended to give 230VAC from 380VAC, but I turned it the other way and put in 0-230VAC at the secondary. That way I can get up to 0-540VDC.
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Old 7th April 2003, 09:14 AM   #26
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Default Load?

In my circuit.. Will the KT88 present a load to the 6N1P? When I just had the 6N1P connected to my cd and my scope, I had almost 120V P-P signal with no indications of clipping. If I connect a probe now when I have the powertube connected I have much less signal. Is this normal? It also looks like can I can drive the 6N1P to clip. But it looks like it is only one side of the sine-waves that clips.

Should I change the bias of the tube so that the signal is in the middle of the usable amplitude-range (so that clipping occurs at the same level on both sides of the wave).

I have a feeling that I have the same problem with my KT88, but since I can't generate enough signal to the KT88 I can't verify that.

Do bias adjustments adjust where on the 0-400VDC the tube operates? Less current running through the tube means it works closer to ground???
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Old 11th April 2003, 12:04 PM   #27
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I've been thinking... Can I use a negative voltage to lift my tubes above ground?

My input-stage clips quite early, but only at one side of the wave. I would like get my signal more in the middle of the usable amplitude-range.
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