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Old 13th May 2007, 10:36 AM   #11
owen is offline owen  United Kingdom
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Shoog,

I'm guessing that you have a few ECL 82's around...

Why not CCS the input triode using the 'tode, and a second set of tubes for output in fixed bias - provided of course by using the 'redundant' triode section.


have fun


Owen
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Old 13th May 2007, 10:42 AM   #12
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The way I have envisaged it each channel would use 2xECL82. The pentodes would be for the outputs and the triodes would be for the LTP. A simple neg supply and SS CCS would be adequate.
The problem with fixed bias on the outputs is that I will be driving a toroidal output transformer so current balance is critical.

Shoog
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Old 13th May 2007, 11:47 AM   #13
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Hi Shoog

Quote:
The MOT's make reasonable chokes but they are big and heavy. Its the secondary that does the choke duty. The problem I could see would be setting the current through the choke - how would you do it without a CCS?
From what I understood of your experience with the MOT's, you used it in a parafeed amplifier. You used the secondary as choke, and let the primary disconnected. The problem I see here is the saturation of the core, as there is DC current flowing through the secondary. The consequence off saturation is that the inductance falls severely.

Reading this

Quote:
I haven't done it myself, but Jeffrey Jackson (Experience Music) has used the filament current of the output tube to cancel the 'idle' flux in an SE transformer. It takes relatively few turns of wire because the filament current is so high compared to the plate current.
from this thread I thought about applying the same trick to the MOT, but with the current being supllied to the primary, as this is disconnected anyway. I would surely use a CCS, as this seems the easiest way. I was curious if you have maybe tested it, or your opinion about feasibility!

Erik
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Old 13th May 2007, 02:37 PM   #14
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Sounds interesting and not something I had really though about. I run my MOT/chokes at 50mA 350V without any issues of note.

I think your idea is certainly worth a thorough investigation and I would be more than interested in the results. Seems that a simple LM317 CCS might be adequate.

Shoog
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Old 13th May 2007, 03:00 PM   #15
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Hi Shoog

Glad you understood my idea, but this is how far my knowledge goes... I do not know about the maths to calculate how much current has to go through the primary winding to cancel the current through the secondary. And if it improves inductance?? It is just not hard to try when one has the amplifier ready and playing, and even less hard for a hard DIY'er as you

Just an idea: I would say that the current through the primary should be the the ratio of the secondary/primary multiplied by the current through the secondary. If the MOT is 220V to 2200V, that implies in a ratio of 10, and 500mA going through the primary. (But, that is just guessing.) I was also thinking about using a lm317..., say that the R of the primary is 10 ohms, 500mA would imply 5V drop over the primary. The lm317 needs a drop of about 3V over it, so one would need 8V. Rectifying and smoothing of the filament voltage could give this value (one could also use a voltage doubler, if higher values of voltage are needed).

As for me testing it... I have been very busy with school last months as a reaction on a chance that appeared with which I may accelerate my graduation (which will be in Chile, maybe I can meet Bas Horneman over there). Besides, I am still working on my 'borg collective' (thanks SY) prototyping rig...sad that it takes two years to develop a prototyping rig - my girlfriend says I could have built about 4 amplifiers in that time, and, well, she is right! But I always liked lego a lot, and this is my new lego!

All with all, I have good memory for 'things to do' so, someday I will try it! (After a CP, a baby huey, a IV DAC stage, a crossover...)

Erik
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Old 13th May 2007, 03:11 PM   #16
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I think the the current conversion would probably be just in the primary to secondary ratio.

My problem is that I can't see myself getting my *** into gear to build anything much apart from a headphone amp. My two current amps are working well and I know the next step up requires serious money which I just don't have. You have to say stop at some point (before the wife walks out).

Shoog
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Old 13th May 2007, 03:18 PM   #17
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Erik said
Quote:
my girlfriend says I could have built about 4 amplifiers in that time
Shoog replied
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before the wife walks out
Some months ago I had a nice meeting in Amsterdam with SY and Morgan Jones and proudly told that my girlfriend allowed me to have large speakers in the living room. But my happiness faded when they warned me that there is a large difference between a girlfriend and a wife. I will try to postpone marriage, but at one point there is no way back...

Erik
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Old 13th May 2007, 06:34 PM   #18
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Just testing my sig.

Shoog
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Old 13th May 2007, 09:01 PM   #19
SY is offline SY  United States
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Quote:
Originally posted by Shoog
Just testing my sig.

Shoog
Far too long. You can do better, I have confidence!
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You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
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Old 14th May 2007, 07:34 AM   #20
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I was thinking that myself.
I will keep it until I squirrel out something better.

Shoog
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