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PostPosted: 18 Jun 2010, 12:50 
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azazello wrote:
For filling input cap every power tube, 6E5P must have Ia = more than 20 ma...

How are you calculating the input current required to drive the GM70 (without using abbreviations)? Where do you get 20 mA?

I can't find any information on the web concerning the input current requirements of power tubes or how to model an equivalent circuit of the input. There is tons of info on output impedance, but nothing I can find on input impedance other than the grid represents an almost infinite resistance in parallel with the inter-electrode capacitance of the tube which I calculate to be less than 100pf for the GM70 [Cin = Cgk + Cgp(A + 1)]. That's all in parallel with the grid resistor.

If that's the case the input current required is about 1mA with almost all of it going through the grid resistor and the capacitance of the tube is negligible. That can't be correct. I'm making a mistake somewhere I know it. What am I missing? Why so much current draw? Where's the current going? I see no path for 20mA of current.

I know I need more current but i can't figure out where it's going!!!

:confused:

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PostPosted: 18 Jun 2010, 12:57 
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azazello wrote:
Everyone know what is D.E. after Univercity

The only DE I know of is the top level domain code for Germany. Never heard of it in the US.

If it's a "doctorate" we call it a PhD.

Where are you getting 20mA?

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PostPosted: 18 Jun 2010, 14:58 
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I tried with 1 to 6 ma 6E5P drive 6S33S and HF didn't sound good /i think that I have good ear/, and gain was small.
Better result was with 9-10 ma, but I decided get mode 25-30 ma /gain was not max, but enough/, where gain is very important,
And this condition satisfied both things...and good sounding depend to sum of some mode factors.

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Hi End is back proportional to the number of composite parts!
Projects: OTL 6AS7 Gen, Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, PP 6005 Gen. Ellectric , headphone ampl. OTL Loftin White 6AS7 RCA....SE E84L& E80CC Siemens&Tel-n.
http://azazello-sound.blogspot.com/


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PostPosted: 18 Jun 2010, 15:12 
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rock4016 wrote:
Have you looked at Gary Pimm's CCS loaded Pentodes? Lots of gain and voltage swing.
http://www.pimmlabs.com/web/drivers.htm

Thanks. I don't understand where the output comes from. It's shown coming out of the middle of the CCS. :confused:
Otherwise it's interesting. I understand the concept of using the CCS, but not the output shown on the schematics on the page. How can you take an output from the "center" of a CCS?

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PostPosted: 18 Jun 2010, 15:17 
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azazello wrote:
I tried with 1 to 6 ma 6E5P drive 6S33S and HF didn't sound good /i think that I have good ear/, and gain was small.
Better result was with 9-10 ma, but I decided get mode 25-30 ma /gain was not max, but enough/, where gain is very important,
And this condition satisfied both things...and good sounding depend to sum of some mode factors.

OK. Now I understand. However, I don't want to experimentally determine the driver current needed for a tube, I want to be able to calculate it and simulate it using a computer model before I build it.

Thanks for clearing that up though. I appreciate it.

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PostPosted: 18 Jun 2010, 15:30 
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Maybe is, IMO, better more experimenting, where You can more fill and determine quality of sound.
/1 question, please....what is better? 1 interstage cap 200nF or 2 parallel 100nF....If calculate this is the same.../

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Hi End is back proportional to the number of composite parts!
Projects: OTL 6AS7 Gen, Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, PP 6005 Gen. Ellectric , headphone ampl. OTL Loftin White 6AS7 RCA....SE E84L& E80CC Siemens&Tel-n.
http://azazello-sound.blogspot.com/


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PostPosted: 18 Jun 2010, 15:40 
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azazello wrote:
Maybe is, IMO, better more experimenting, where You can more fill and determine quality of sound.
/1 question, please....what is better? 1 interstage cap 200nF or 2 parallel 100nF....If calculate this is the same.../

To the best of my knowledge if the caps are the same type and value you can parallel two to double the capacitance.

However, if the caps are of different values or types you may get resonant effects that screw up your frequency response.

It's best to use a single 200nf, but if identical, two 100s will work. However, there's no such thing as "identical" caps, but in practicality it should work fine as long as they are "almost" the same.

I assume your talking about a cap in the signal path.

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PostPosted: 18 Jun 2010, 15:56 
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My knowledge show me, if we use one brand caps, usually, IMO, 2 x 100 sounds better, because 100 is faster on HF, that 200.....Somebody use smaller cap 22 nF, parallel to 200nF to accelerate HF...But efect is NO if You use 220 nF.....sorry for off!

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Hi End is back proportional to the number of composite parts!
Projects: OTL 6AS7 Gen, Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, PP 6005 Gen. Ellectric , headphone ampl. OTL Loftin White 6AS7 RCA....SE E84L& E80CC Siemens&Tel-n.
http://azazello-sound.blogspot.com/


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PostPosted: 18 Jun 2010, 21:12 
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azazello wrote:
My knowledge show me, if we use one brand caps, usually, IMO, 2 x 100 sounds better, because 100 is faster on HF, that 200.....Somebody use smaller cap 22 nF, parallel to 200nF to accelerate HF...But efect is NO if You use 220 nF.....sorry for off!

That's ok for off. I have to say based on everything I know about caps (which is not a lot but is slowly and steadily increasing) that two parallel caps of the same type and size should sound the same as one of the exact same type. When you have one 100nf the highs may be more detailed becasue it's "fast". But it's "fast" ONLY because the capacitance is low. When you add the second 100nf cap, you are now "slowing down" the first cap and the "speed" which is related to the TOTAL CAPACITANCE will be the same as one 200nf.

It might sound different, but not becasue it's "faster" IMHO. That effect may be important where a large slow (electrolytic) cap is in parallel with a much smaller fast cap, and maybe even with a 200 and a 20, but if the caps are of the same type, size and dielectric I don't buy the explanation, although I don't doubt you hear a difference.

My explanation is you are creating resonant peaks with different capacitors in parallel due to the interaction of their inductive properties and it's causing a slight boost in the highs, but it's an unnatural, artificial, unpredictable boost that may affect each channel differently, and your results would be more consistent with one good quality cap. That's my best hypothesis at least.

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PostPosted: 18 Jun 2010, 21:25 
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Back to the topic at hand.

The trannys will be here soon and the amp is under construction. The high voltage CCS is a huge success,

It looks like I've got the driver figured out, I've got a new SRPP stage designed using a CCS Bruce turned me onto (thanks!) so I'll have 4 CCSs in my amp with possibly even lower distortion that the Oddwatt SRPP ??? :wizard: (probablyt not)
and I'll leave this alone until I have some photos and more important developments.

Azazello, PM me for off topic. Thanks.

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