HT ripple measurement

 Measuring HT supply ripple with your Sound Card

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Despite having used the Pete Millett’s SC interface to measure HT supply ripple, it does have a limitation as the input capacitor is rated 400V. Morgan Jones recommends on his latest great “Building Valve Amplifiers” (second edition) three methods for doing this. I opted the one shown above as it does help rejecting common mode noise and also protecting the SC interface. I’m careful enough to not revert the input by accident. If that should happen, the transformer used in this case provides a 500VAC (700VDC) isolation. Normally I play around 400-600V, so should survive in case of misuse. I played with LTSpice to tweak the secondary resistor down to 200Ω when input capacitance is raised to 10μF. Other transformers may allow reducing size of capacitor and increasing resistor up to 10KΩ. I have an OEP E187F at hand so this is what I will use.  f-3dB is about 30Hz and provides flat response at 50Hz and 100Hz to measure accurately input ripple.

Will build and report 🙂

Input capacitance

Drive Mr. Miller, drive…

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Input capacitance test rig

Whilst designing triode driver stages for a 300B SE amplifier, I looked into the input capacitance of high-mu triode (or triode-strapped pentodes) that are suitable candidates here. We know Miller capacitance is the big drawback of the triode driver stage, so I kind of liked the idea of testing how much this capacitance could be for the lovely Russian triode-strapped pentodes like 6e5p, 6e6p, 6j11p, 6j5p, 6j52p, etc.

Continue reading “Input capacitance”

DL103 cartridge review

IMG_1416This may not be any news to most of you, but after a long time I managed to get the upgrade needed on my turntable: the cartridge. The Denon DL103 was a perfect decision to step up into the MC territory at an affordable cost. Many will say out there that there are better cartridges, but that is not the point of my review.

I tried some MM ones and until now couldn’t get the Lenco + Audiomods arm to sound as good as it sounds now. The DL103 is challenging due to its low compliance and output levels.
IMG_1414

Although I have a step-up transformer, I’m saving it for my valve phono stage project which I hopefully will get my hands on next year. Currently still have a solid stage RIAA stage made by Project which sounds really good in my opinion. Shortly will complete my JFET shunt cascode RIAA stage and listen to the difference.

Jeff from Audiomods sent me the copper shim for the headshell but my cartridge screws aren’t long enough to fit both. I was worried on the performance by not adding sufficent mass to the arm, but after testing it, I was surprised to see that it was not the case.

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The sound performance is really good. No loss in bass or treble, with a flat response, the dynamics are brilliant. Noise level is very low.  Tight drums and clearer sound. I like the detail and even playing loud sections it is great.  I will continue to listen to this until I can find anything to dislike from it, so far it’s superb.

 

New Lundahl distributor in UK

I’m pleased to see Big Bear Audio to start the distribution of the Lundahl transformers in the UK. I’ve got my first order and everything went really smooth. A fantastic service from Big Bear Audio.

Highly recommended, Big Bear Audio is now my new iron supplier!

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814 SE A2 Amplifier

Goodbye 4-65a SE, at least for now

IMG_1401After enjoying the 4-65a SE amplifier for many months, I couldn’t resist myself from upgrading the output stage to the 814s.  I just needed changing sockets and filament raw supply transformers to fit the requirements of this lovely transmitting valve. Needless to say, my recent tests on 814s were very encouraging. The 814 seemed to perform much better than the 4-65a in delivering 10W of class A2 sound at half the distortion levels. This to me, was only worth trying.

Continue reading “814 SE A2 Amplifier”

6ж52п / 6Z52P in triode mode

I have only one 6ж52п which measures within specs:

Operating point in pentode:

  1. Ia=42.1mA @ Va=150V/Vs=150V
  2. gm=4.47mA/V
  3. Is=4.4mA

Triode curves:

6z52p triode

 

Triode SPICE model:

6z52p triode SPICE model-published

 

And resulting SPICE model:

**** 6Z52P TRIODE ******************************************
* Created on 11/17/2013 19:25 using paint_kit.jar Version 2.4 Beta. May 2013 
* Curve traced and model by Ale Moglia 2013 [email protected]
* Curves image file: 6Z52P TRIODE
* Data source link: www.bartola.co.uk/valves 
*----------------------------------------------------------------------------------
.SUBCKT TRIODE_6Z52P 1 2 3 ; Plate Grid Cathode
+ PARAMS: CCG=13.5P CGP=0.5P CCP=2P RGI=2000
+ MU=76.5 KG1=34.7 KP=252 KVB=1272 VCT=-0.11 EX=1.39 
* Vp_MAX=200 Ip_MAX=200 Vg_step=0.5 Vg_start=0 Vg_count=8
* Rp=4000 Vg_ac=55 P_max=11.2 Vg_qui=-48
* X_MIN=64 Y_MIN=48 X_SIZE=421 Y_SIZE=530 FSZ_X=995 FSZ_Y=675 XYGrid=false
*----------------------------------------------------------------------------------
E1 7 0 VALUE={V(1,3)/KP*LOG(1+EXP(KP*(1/MU+(VCT+V(2,3))/SQRT(KVB+V(1,3)*V(1,3)))))} 
RE1 7 0 1G ; TO AVOID FLOATING NODES
G1 1 3 VALUE={(PWR(V(7),EX)+PWRS(V(7),EX))/KG1} 
RCP 1 3 1G ; TO AVOID FLOATING NODES
C1 2 3 {CCG} ; CATHODE-GRID 
C2 2 1 {CGP} ; GRID=PLATE 
C3 1 3 {CCP} ; CATHODE-PLATE 
D3 5 3 DX ; POSITIVE GRID CURRENT 
R1 2 5 {RGI} ; POSITIVE GRID CURRENT 
.MODEL DX D(IS=1N RS=1 CJO=10PF TT=1N) 
.ENDS 
*$

814 SE A2 Amplifier (Part 1)

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816 in triode mode

It’s time for the leap of faith. Having tested the 814 in triode mode, I will proceed now to upgrade my 4-65a SE amplifier and replace output valve for the 814. To ensure it can withstand the 540V in the anode, the remaining grids are all tied together through a resistor to the anode. All grids and anode are fitted with ferrite beads as well. A pair of UF4007 in series are placed to protect the Output Transformer in case load is accidentally disconnected.

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UX5 socket prepared

I added to the UX-5 socket a small bar to place two turrets to provide the anode (top connector), the strapped grid connections through the wire-wound resistor and the pair of UF4007 diodes.

Given that the 814 will run @ 540V / 100mA, I will only need to adjust the Rod Coleman regulators to set current down to 3.25A after replacing the raw filament transformers, as the 814 are 10V instead of 6V filaments of the 4-65a.

Minor DC adjustment will be required on the driver circuit via the gyrator load, so can easily implement this new amplifier.

Stay tuned…

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814 ready to go