Parts arrived - 6H3n-EB Russian tubes, 6DJ8 China tubes and adapters, 5V and 9v smps regulators, schottky diodes and 680uF 63V caps - couldn't get 80V that would fit :-(
I replaced the 4 FR diodes in the voltage multiplier with schottkys to boost the supply voltage by about 1V on each rail.
I tried the 5V regs as drop in for the 7805 but they didn't work with the two diodes at the ground pin. So they came out and I fitted the 9V smps in series with the 7805. This kept the filament heater at 6.26V but with a lower overall current demand for the buffer from 380mA to 260mA on a 0-12VAC supply. With no heatsink, the 7805 temperature was still climbing when I switched off at 75degC, so I fitted a very small heatsink to the 7805 and ran it for 30mins - it peaks at 64degC in free air with ambient at 22degC. The smps gets slightly warm. So now the board is ready for higher input voltages without overheating the 7805.
Next will be to replace all the 220uF with 680uF to lower ripple. The voltage multiplier is 3x, so 0-18VAC will be fine, but with low ripple and stable mains, I might get away with 0-20V.
I replaced the 4 FR diodes in the voltage multiplier with schottkys to boost the supply voltage by about 1V on each rail.
I tried the 5V regs as drop in for the 7805 but they didn't work with the two diodes at the ground pin. So they came out and I fitted the 9V smps in series with the 7805. This kept the filament heater at 6.26V but with a lower overall current demand for the buffer from 380mA to 260mA on a 0-12VAC supply. With no heatsink, the 7805 temperature was still climbing when I switched off at 75degC, so I fitted a very small heatsink to the 7805 and ran it for 30mins - it peaks at 64degC in free air with ambient at 22degC. The smps gets slightly warm. So now the board is ready for higher input voltages without overheating the 7805.
Next will be to replace all the 220uF with 680uF to lower ripple. The voltage multiplier is 3x, so 0-18VAC will be fine, but with low ripple and stable mains, I might get away with 0-20V.
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So with caps fitted and 0-15VAC (measured at 16VAC), I get 3mV ripple on 41V supply rails, with 30mV ripple before the cap multiplier/current limiting transistors, with a 190mA total demand for the buffer. But with 0-18VAC (measured at 17.8VAC) I get 200mA demand and 45V supply rails with the same ripple. A bit odd - I expected 47V or so, and lower, not higher, current demand. I can't explain that except perhaps that the transformer is being overloaded, but then why is the AC 17.8V? Is it the tube's behaviour? I removed it and found the rails rose to 48.5V DC so I guess these tubes "come on cam" like an engine and start drawing more when they are "at peak torque" and this is pulling down the voltages. Is that a reasonable analogy? I haven't chnaged the resistors to suit higher voltages so if they are drawing more current, I guess the lower voltages are across the cathodes resistors. So the tube went back in and I measured that at 1.1V whereas it was 0.8V before. Hmmm. Could the current limiter be interfering? It's 33R over 0.6V so 18mA. BTW I don't have 0-20VAC to try. I don't dare try 0-24VAC.
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Sorry for the multiple posts but I have achieved the maximum supply for the parts I have 
A 0-24VAC 30VA transformer with 7.5R 10W resistor in series creates 24.1VAC max on the input after warm up of 20 mins. This puts 60.8V DC max across the caps, with 35mV ripple. This in turn creates 57.8V supply rails for the tube with 0.000mV ripple (below Fluke DMM sensitivity). Current draw is 150mA to 160mA and the voltage drop across the bias resistor is 1.56V. So there is roughly 74V across the tube now.
I have hopes to use this buffer as part of an MM stage so it only needs 20mV or so of input voltage swing - changing the bias resistor accordingly should help raise the voltage across the tube too. The next stage is to tailor the resistors for a given tube. I have the China 6N3, 6DJ8 and Russian 6H3n-EB - I can see the attraction of tubes over op amps - the latter all look largely the same but tubes are far more fascinating. And I've gotta say, I really appreciate the aesthetics not only of the tube but the Russian boxes and wrapping paper. I got a Tony Hancock radio ham moment. "Now then, where are me radio valves?" YouTube
PS Any tips for using this a phono buffer?
A 0-24VAC 30VA transformer with 7.5R 10W resistor in series creates 24.1VAC max on the input after warm up of 20 mins. This puts 60.8V DC max across the caps, with 35mV ripple. This in turn creates 57.8V supply rails for the tube with 0.000mV ripple (below Fluke DMM sensitivity). Current draw is 150mA to 160mA and the voltage drop across the bias resistor is 1.56V. So there is roughly 74V across the tube now. I have hopes to use this buffer as part of an MM stage so it only needs 20mV or so of input voltage swing - changing the bias resistor accordingly should help raise the voltage across the tube too. The next stage is to tailor the resistors for a given tube. I have the China 6N3, 6DJ8 and Russian 6H3n-EB - I can see the attraction of tubes over op amps - the latter all look largely the same but tubes are far more fascinating. And I've gotta say, I really appreciate the aesthetics not only of the tube but the Russian boxes and wrapping paper. I got a Tony Hancock radio ham moment. "Now then, where are me radio valves?" YouTube
PS Any tips for using this a phono buffer?
Attachments
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I had this ZeroZone board for some time, but never bothered to solder it. I did now, and measured it a little with ARTA.
It certainly gives some 'tube spice' to the sound. Distortion is high, 2nd harmonic highest, and then falling. The best I can get is abt -60dB to the 2nd harmonic at low output levels (20mV RMS), and with more output, distortion is slowly rising to -20dB at 1V RMS out.. then there is a whole spectrum of harmoncis in the FFT. The negative peak of the sine starts 'soft clipping' first, and there is visible distortion on the scope at 1V.
This is the unmodified board, and filament voltage is 5V. Both channels are similar.
It certainly gives some 'tube spice' to the sound. Distortion is high, 2nd harmonic highest, and then falling. The best I can get is abt -60dB to the 2nd harmonic at low output levels (20mV RMS), and with more output, distortion is slowly rising to -20dB at 1V RMS out.. then there is a whole spectrum of harmoncis in the FFT. The negative peak of the sine starts 'soft clipping' first, and there is visible distortion on the scope at 1V.
This is the unmodified board, and filament voltage is 5V. Both channels are similar.
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I know the thread is quite old but the board costs 15Eur on Ali. So, I could not resist not to buy it. Here are my 5 cents. Maybe, they will be useful for someone else.
I got rid of current limiter in anode (mutiplier) voltage circuit. Someone in this thread spotted it earlier In order to do this, the 2nd transistor, 33R and 330R resistors should not be soldered. Instead of the resistors, the jumpers should be soldered.
In my kit, instead of 4.7K going to the transistor base, a 4.7R was given. I used my own 4.7. I put the jumpers instead of input 474 caps as I know there are output caps in my DAC. I used my output caps instead of supplied. The supplied J-grade Chinese 6N3 is nothing interesting and quite muddy, suitable only to test the circuit if it works. I used Russian 6N3P-EV, which is mentioned above.
After doing, I do not want to unplug from my system
Originally bought this board in order to convert it into gain stage, putting the Mosfets follower after it to make the hybrid headphone amplifier.
I got rid of current limiter in anode (mutiplier) voltage circuit. Someone in this thread spotted it earlier
In order to do this, the 2nd transistor, 33R and 330R resistors should not be soldered. Instead of the resistors, the jumpers should be soldered.In my kit, instead of 4.7K going to the transistor base, a 4.7R was given. I used my own 4.7. I put the jumpers instead of input 474 caps as I know there are output caps in my DAC. I used my output caps instead of supplied. The supplied J-grade Chinese 6N3 is nothing interesting and quite muddy, suitable only to test the circuit if it works. I used Russian 6N3P-EV, which is mentioned above.
After doing, I do not want to unplug from my system
Originally bought this board in order to convert it into gain stage, putting the Mosfets follower after it to make the hybrid headphone amplifier.
Did I make zhe correct 6J4WA model?
Did I make zhe correct 6J4WA model?
MODE:
**** 6J4WA ******************************************
* Created on 11/29/2021 13:49 using paint_kit.jar 3.1
* Model Paint Tools: Trace Tube Parameters over Plate Curves, Interactively
* Plate Curves image file: 6J4WA.JPG
* Data source link:
*----------------------------------------------------------------------------------
.SUBCKT TRIODE_6J4WA 1 2 3 ; Plate Grid Cathode
+ PARAMS: CCG=3P CGP=1.4P CCP=1.9P RGI=2000
+ MU=7.568 KG1=1908.08 KP=20 KVB=0.01465 VCT=7.812E-5 EX=1.204
* Vp_MAX=300 Ip_MAX=40 Vg_step=15 Vg_start=0 Vg_count=5
* Rp=4000 Vg_ac=55 P_max=40 Vg_qui=-48 Vp_qui=300
* X_MIN=32 Y_MIN=52 X_SIZE=602 Y_SIZE=405 FSZ_X=1149 FSZ_Y=600 XYGrid=false
* showLoadLine=n showIp=y isDHT=n isPP=n isAsymPP=n showDissipLimit=y
* showIg1=n gridLevel2=n isInputSnapped=n
* XYProjections=n harmonicPlot=n dissipPlot=n
*----------------------------------------------------------------------------------
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
*$
Did I make zhe correct 6J4WA model?
MODE:
**** 6J4WA ******************************************
* Created on 11/29/2021 13:49 using paint_kit.jar 3.1
* Model Paint Tools: Trace Tube Parameters over Plate Curves, Interactively
* Plate Curves image file: 6J4WA.JPG
* Data source link:
*----------------------------------------------------------------------------------
.SUBCKT TRIODE_6J4WA 1 2 3 ; Plate Grid Cathode
+ PARAMS: CCG=3P CGP=1.4P CCP=1.9P RGI=2000
+ MU=7.568 KG1=1908.08 KP=20 KVB=0.01465 VCT=7.812E-5 EX=1.204
* Vp_MAX=300 Ip_MAX=40 Vg_step=15 Vg_start=0 Vg_count=5
* Rp=4000 Vg_ac=55 P_max=40 Vg_qui=-48 Vp_qui=300
* X_MIN=32 Y_MIN=52 X_SIZE=602 Y_SIZE=405 FSZ_X=1149 FSZ_Y=600 XYGrid=false
* showLoadLine=n showIp=y isDHT=n isPP=n isAsymPP=n showDissipLimit=y
* showIg1=n gridLevel2=n isInputSnapped=n
* XYProjections=n harmonicPlot=n dissipPlot=n
*----------------------------------------------------------------------------------
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
*$
Hi. What if remove blue LED? It's affecting something?
Hi.
Blue LED is useful because it is powered by the 6.3V DC Heater supply line and we still see the "orange" glow at the "side" of the glass.
The Red LED is powered by the AC line with a diode and a 1kOhm resistor.
I reckon that the Nichicon Fine Gold (330uF/50V) at the voltage quadruple (Two Greinacher cells) must have more burning time, as the Elna Silmic II (4.7uF/50V) at the input and output for DC decoupling.
Better sockets for interconnectors also help, but for now I just take as it is...
Old post I know..
The 2c51 has the same pinout and stunds much better.I use them in a preamp.
I bought this buffer a year ago but only soldered it together.
I have not tried it yet.