Looking for a SRPP Calculator - diyAudio
 Looking for a SRPP Calculator
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 9th August 2015, 11:42 PM #1 diyAudio Member   Join Date: Jul 2009 Looking for a SRPP Calculator Hi I am looking for a SRPP calculator for 12AX7 & 420a, I am not so good to just getting ibea from raw tube information, thanks. I have a project to rebuild first stage of a tube amp and plan to use 420a.
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Join Date: Dec 2014
Location: London
here
Attached Files
 tube calc.zip (95.3 KB, 47 views)

 10th August 2015, 03:22 PM #3 diyAudio Member   Join Date: Jun 2014 Location: Paris, France Hi I am sorry to say that this SRPP calculator is wrong. At least there are 2 mistakes. 1 - Rg2 should be a short 2- the output résistance (at top of Rk2) is much more smaller than the value given by the calculator Regards
 10th August 2015, 03:43 PM #4 diyAudio Member   Join Date: Jul 2009 Thanks, it’s still a great step forward.
 10th August 2015, 04:32 PM #5 diyAudio Member   Join Date: Jun 2014 Location: Paris, France Hi I would like to say that in order to get the benefit of a low distortion level produced by the SRPP topology, the 2 tubes shall work in the same conditions and for this, Rk2 shall equal Rk1=Rk. In this situation, the output resistance ( at top of Rk2) is given by : rs=(Ri/2) * (Ri+(2+µ)Rk) / (Ri+(1+mu) Rk) soit proche de Ri/2 Regards
 10th August 2015, 05:22 PM #6 diyAudio Member   Join Date: Jun 2014 Location: Paris, France Hi I have to add that the formula I gave last post is with no capacitor in parallel with Rk1 With capacitor Ck in parallel with Rk1 ( and no capacitor in // with Rk2 ), the output resistance is given by : rs=Ri*(Rk2+Ri) / (2 Ri+(1+µ) Rk2) And with capacitor Ck on both Rk=Rk1=Rk2 rs=Ri/2 Personaly, I avoid capacitors and I use a 6SN7 to do the job, less voltage gain but lower output resistance than with a 12AX7. Regards
 10th August 2015, 05:29 PM #7 diyAudio Member   Join Date: Jan 2003 Location: Sweden [QUOTEI am sorry to say that this SRPP calculator is wrong. [/QUOTE] That is not the only fault in the calculator, as an example Cmiller is wrongly calculated for cathode followers, there can be other faults so be careful when using this.
diyAudio Member

Join Date: Mar 2004
Location: Budapest, Hungary
SRPP calculator

The attached Excel table proved to be accurate. Conditions: Rk1 = Rk2, there is no Ck1 parallel to Rk1.
Attached Files
 SRPP.zip (12.9 KB, 24 views)

 12th August 2015, 09:38 AM #9 diyAudio Member   Join Date: Jun 2014 Location: Paris, France Hi @Icsaszar According to the definition of output impedance, it shall not include the load RL as I can read in the file (column L). Is my reading correct ?
diyAudio Member

Join Date: Mar 2004
Location: Budapest, Hungary
Quote:
 Originally Posted by Hyperman75 Hi @Icsaszar According to the definition of output impedance, it shall not include the load RL as I can read in the file (column L). Is my reading correct ?
That is correct. The output impedance is the unloaded source impedance. The equations came from the Tube CAD Journal, May 2000 issue, available online. It seems I made a mistake when I put them in the Excel. Uploaded is the fixed version.
Attached Files
 SRPP.zip (16.5 KB, 15 views)

Last edited by lcsaszar; 12th August 2015 at 01:02 PM. Reason: error in the calculation

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