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Old 27th March 2012, 02:23 PM   #161
SY is offline SY  United States
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Quote:
Originally Posted by ashok View Post
Yes I'll try that. I'll pick up a bottle of the 'stuff' soon.
If peroxide can bleach skin pigments ( I'm brown ...will tell easily !) then this one may not be it as it didn't bleach my skin or leave any marks. Just felt like a burning sensation when it touched the skin until washed off with water.
I have some 10% H202 here but that's too dilute to bleach skin pigments!
Did it feel soapy on your skin?

For the others, once an enamel is set and cured, a solvent won't affect it much. You can only corrode it off.
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Old 28th March 2012, 12:28 AM   #162
popilin is offline popilin  Argentina
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Originally Posted by SY View Post
Solvent won't do it- the enamel is a thermoset. You're stuck with abrasion or scraping. Sorry.
Hi Sy
You are right.
With patience, I burned the enamel with a cigarette lighter, then sanded with steel wool, so I could solder.
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Old 28th March 2012, 12:38 AM   #163
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since i build all power traffos for my tube builds, i actually use this box cutter, i scrape the magnet wires using the side of the blade, not the cutting side of the blade itself if you get what i mean....
Click the image to open in full size.
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Old 28th March 2012, 12:47 AM   #164
popilin is offline popilin  Argentina
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Hi Tony
Already tried a cutter, only serves to thick wires, remove too much copper.
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Old 28th March 2012, 01:34 AM   #165
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Try soaking in acetone tips of wires overnight, put them between lid and neck of smal bottle. I disassembled such a way HF transformers, after 2 days in can with acetone epoxy is softer and breaks easily.

Also, fine sand paper helps. Bend it twice, put wires between, squeeze by finger tips and pull jently.
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Old 28th March 2012, 01:41 AM   #166
popilin is offline popilin  Argentina
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Hi Wavebourn
You always with a new trick, I will try this.
Oh, once have you used tar for potting?
I traveled 400 km today, to buy epoxy and did not get it
Thanks

Last edited by popilin; 28th March 2012 at 02:08 AM.
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Old 28th March 2012, 06:20 AM   #167
AJT is offline AJT  Philippines
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Originally Posted by popilin View Post
Hi Tony
Already tried a cutter, only serves to thick wires, remove too much copper.

i use them for coppers from gage 8 to 32, from 32 down to 38 i merely scratch the copper, enough to solder them unto tags or pigtails....

the thicker wires, 20 and up need more working....
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Old 28th March 2012, 07:03 AM   #168
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Hi all
I think a lot of posts should be moved to a new thread.
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Old 28th March 2012, 06:31 PM   #169
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Back to the topic, maybe.
Not to step on toes sometimes the “best” most linier out of the NOS box triode is the best pick. Then we add the best Solid State Constant Current Source or Mu follower to draw straight load lines across the assumed grid curves. The effort here is to design the best possible stand alone device, say an riaa equalization pre-amplifier.

Now to question the assumptions regarding a one size fits all triode distortion test jig. The Morgan Jones medium mu test method produces valid results for a restricted set of assumptions and conditions. If the tube has a chance at 8 milliamps it may test well. If the circuit you are building does not operate at a constant 8ma your results may vary.

I play with this stuff because I like tweaking the old technology and adjusting my understanding of what I know. (Adjusting my assumptions and the assumption of others) I also like the old musty texts with graphics and calculus.

I like this old musty article George Fletcher Cooper.

http://tubecad.com/2005/March/02/Whi...%20I%20Use.pdf

The performance of the tube depends on the circuit that supports it. An example of this is parameter restriction by the use of a Constant Current Source. Another example is the 180 degree out of phase series triodes like in the SRPP circuit in this thread. George Cooper points out that to minimize a pentode or triode distortion select a tube with a ruler straight graph of grid voltage to transconductance, or to select an operational point in the center straight portion of that curve. Then George points out that the addition of a cathode resistor with change curve rate of the graph of grid voltage to transconductance and the total content of 3rd harmonic. The selection of the correct cathode resistor and grid voltage will minimize the 3rd harmonic. This was news to me when I read it. For grins I put this in the simulator with my favorite triode at the time. It was interesting to observe the 3rd harmonic and higher nearly disappear with the adjustment of the cathode resistor and or putting a resistor in series with a cathode resistor bypass capacitor. Not much happened to the 2nd harmonic with the adjustment of the cathode resistor. Putting two triodes in series (SRPP) reduced the second harmonic, selection of the cathode resistors and B+ voltage to set the grid voltage and plate current reduced the 3rd and higher harmonics.

From the point of view of tweaking a tube and support circuit for optimum performance the 12AU7 is a perfect tube to play with. A perfect tube has less to play with. I do think that there is an electron cloud in there as well.
DT
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Old 29th March 2012, 03:38 AM   #170
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Hi DualTriode
I agree with you on what you say, a perfect tube has less to play with, and of course there is an electron cloud in there. (I do not want to talk about it)

Very good article and very good your approach.
Unfortunately, almost no datasheets are achieved with gm vs Vg curves, so making implementation difficult, as with traditional methods, plus the fact that in the real world, valves are different from what the datasheet says, there is not a huge difference compared to simulations, so the only way is to test and measure.

I can not make many measurements, just this year gave me an old scope, now it makes sense to build a signal generator.
With all that against me, simulations make much sense, also needed a rule of thumb, mine is working with the highest allowed +B and remain below dissipation limit curve, you already know the reason, that was the subject of much debate.
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