This kind of question needs an up to date schematic, to determine where we are at, and where we are going.
But I will make the assumption that we are talking about a Decware EL84 SE stereo amplifier, or similar.
An OD3 or OD3A can easily supply approximately 150V (+/- 2.75 Volts versus load current variation), and if the OD3 is set to 17.5mA current, it can supply up to 17.5mA to the load, and can still be within the OD3/A dissipation limit if the load drops to 0 mA.
That ought to be able to regulate the B+ of both input tubes of any Decware EL84 stereo amp (if the input tubes and their plate load resistors can work properly with only 150V B+.
If someone says you need a separate OD3/A for each input triode, then I would ask you to listen to the finest Vinyl playback system in the world.
A single OD3/A should have far in excess of 60 dB separation of the B+ voltage, if the rest of the amplifier circuitry and wiring has at least that much separation to allow us to know that the L and R input B+ separation is that good.
That best in the world LP playback system might have up to 35 dB or 40 dB separation on some records at 1kHz, but it will certainly have much, much less separation at both the bass frequencies and high pitch instruments, and their high harmonic frequencies of that same really good record (not only cutter mechanics limited, but also tone arm limited, and phono cartridge limited). Good luck getting 40 dB separation of all the frequencies that come off the Vinyl.
I once designed and built a stereo single ended 45 amplifier that intrinsically had (by design) 40 dB of separation from 20Hz to 20kHz.
I got great and wonderful comments on the sound, and nobody ever complained about the 40 dB of separation.
Think of improvements/modifications to any amplifier like this . . .
An onion has the outer layer, middle layers, and the core layer.
Start by improving tjhe amplifier at the outer layer, then move to the middle layers, before even considering 'fixing' the core layer.
The other option is to start with a different onion.
(I wish I still had that 45 amp I designed and built).
But I will make the assumption that we are talking about a Decware EL84 SE stereo amplifier, or similar.
An OD3 or OD3A can easily supply approximately 150V (+/- 2.75 Volts versus load current variation), and if the OD3 is set to 17.5mA current, it can supply up to 17.5mA to the load, and can still be within the OD3/A dissipation limit if the load drops to 0 mA.
That ought to be able to regulate the B+ of both input tubes of any Decware EL84 stereo amp (if the input tubes and their plate load resistors can work properly with only 150V B+.
If someone says you need a separate OD3/A for each input triode, then I would ask you to listen to the finest Vinyl playback system in the world.
A single OD3/A should have far in excess of 60 dB separation of the B+ voltage, if the rest of the amplifier circuitry and wiring has at least that much separation to allow us to know that the L and R input B+ separation is that good.
That best in the world LP playback system might have up to 35 dB or 40 dB separation on some records at 1kHz, but it will certainly have much, much less separation at both the bass frequencies and high pitch instruments, and their high harmonic frequencies of that same really good record (not only cutter mechanics limited, but also tone arm limited, and phono cartridge limited). Good luck getting 40 dB separation of all the frequencies that come off the Vinyl.
I once designed and built a stereo single ended 45 amplifier that intrinsically had (by design) 40 dB of separation from 20Hz to 20kHz.
I got great and wonderful comments on the sound, and nobody ever complained about the 40 dB of separation.
Think of improvements/modifications to any amplifier like this . . .
An onion has the outer layer, middle layers, and the core layer.
Start by improving tjhe amplifier at the outer layer, then move to the middle layers, before even considering 'fixing' the core layer.
The other option is to start with a different onion.
(I wish I still had that 45 amp I designed and built).
Yes, I am referring to the schematic from the Zkit1 page:
The same Decware forum thread ans page I referred to last post also states:
"The Zens only draw around 50 mA on average from that 170mA power supply. Some are built with a resistor, some are built with chokes, and none have run this cool. In fact the original zen ran hot.
The only explanation I can offer is that both the resistor(s) and or the choke reflect something backwards back into the transformer through the bridge rectifier which causes friction/heat that isn't necessarily tied to load.
In any case with it running so cool I have no qualms about leaving it on 24 hours a day and it makes sense that without the chaos of this friction, the sound would have insane liquidity - almost disarming.
The reason there is none of this is because I have eliminated the resistors and the choke and am using the vacuum gap of the OA3 tube in place of it to feed high voltage to the plate of each output tube. This has never been done before, only the grids of the output tubes, or the high voltage for the input tubes has ever been done in the past. In this amp all the high voltage for everything is resistor-less and has no chokes, just the vacuum gaps of three separate vacuum regulator tubes, one for each output tube and one for the input tube.
Of course this can not be done with any other amplifier because all other amplifiers use larger output tubes, and we're at the limit of the current capacity of the Voltage Regulator tube with the Zen's 6P15P-EB / EL84 output tube. So something this graceful can only be done on a 2 watt Zen Triode Amplifier."
And the OA3's (75V) goes to the output tubes (SV83 or EL84), the OD3a (150V) to the input tube (7DJ8 or 6N1P). I don't really get how this is possible: 75V on the output tubes are way lower than original. But if positioned as a replacement of the 1k/5W resistor after the rectifier, before the outut transformer, this might make sense....? The voltage drop over this one is 75V given a current draw of 75mA on the secondary side of the transformer..
The same Decware forum thread ans page I referred to last post also states:
"The Zens only draw around 50 mA on average from that 170mA power supply. Some are built with a resistor, some are built with chokes, and none have run this cool. In fact the original zen ran hot.
The only explanation I can offer is that both the resistor(s) and or the choke reflect something backwards back into the transformer through the bridge rectifier which causes friction/heat that isn't necessarily tied to load.
In any case with it running so cool I have no qualms about leaving it on 24 hours a day and it makes sense that without the chaos of this friction, the sound would have insane liquidity - almost disarming.
The reason there is none of this is because I have eliminated the resistors and the choke and am using the vacuum gap of the OA3 tube in place of it to feed high voltage to the plate of each output tube. This has never been done before, only the grids of the output tubes, or the high voltage for the input tubes has ever been done in the past. In this amp all the high voltage for everything is resistor-less and has no chokes, just the vacuum gaps of three separate vacuum regulator tubes, one for each output tube and one for the input tube.
Of course this can not be done with any other amplifier because all other amplifiers use larger output tubes, and we're at the limit of the current capacity of the Voltage Regulator tube with the Zen's 6P15P-EB / EL84 output tube. So something this graceful can only be done on a 2 watt Zen Triode Amplifier."
And the OA3's (75V) goes to the output tubes (SV83 or EL84), the OD3a (150V) to the input tube (7DJ8 or 6N1P). I don't really get how this is possible: 75V on the output tubes are way lower than original. But if positioned as a replacement of the 1k/5W resistor after the rectifier, before the outut transformer, this might make sense....? The voltage drop over this one is 75V given a current draw of 75mA on the secondary side of the transformer..
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Sorry about the two attachments in the post above, I did not intend for them to be attached and cannot find a way to edit it..
Another question, regarding the power transformer: Recommended type is Edcor XPWR066-240: https://edcorusa.com/products/xpwr066-600v-200ma-ct-6-3v-4a-5v-3a
Is the Hammond 372HX similar? http://www.hammondmfg.com/pdf/EDB372HX.pdf and http://www.hammondmfg.com/300series.htm
I will be using 240V AC on primary side.
Another question, regarding the power transformer: Recommended type is Edcor XPWR066-240: https://edcorusa.com/products/xpwr066-600v-200ma-ct-6-3v-4a-5v-3a
Is the Hammond 372HX similar? http://www.hammondmfg.com/pdf/EDB372HX.pdf and http://www.hammondmfg.com/300series.htm
I will be using 240V AC on primary side.
To try and answer my own question, I made the schematic below:
This is what I can interpret from the Decware forum (https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1510887200/66). As the designer comments; it is an unconventional way to use voltage regulator tubes. And I have to comment I am new to tubes, so I am not sure if this seems ok or not. It deviates some from the Zkit1 and the UFO schematics, but the main principles are intact. The use of capacitors is probably theroretically exaggerated, but this is also commented as important for the end product. The number of capacitors is commented, however the exact use of them I am not sure of - this is my interpretation.
Please comment. It would be interesting to build and test this.
This is what I can interpret from the Decware forum (https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1510887200/66). As the designer comments; it is an unconventional way to use voltage regulator tubes. And I have to comment I am new to tubes, so I am not sure if this seems ok or not. It deviates some from the Zkit1 and the UFO schematics, but the main principles are intact. The use of capacitors is probably theroretically exaggerated, but this is also commented as important for the end product. The number of capacitors is commented, however the exact use of them I am not sure of - this is my interpretation.
Please comment. It would be interesting to build and test this.
Solvt,
As you have drawn the schematic . . .
Those regulator tubes provide a relatively constant voltage drop from whatever the B+ voltage is.
OA3 drops about 75V, and changes by 5V from that (higher than 75V with 5 mA load current, and lower than 75V with 40 mA load current).
OD3 drops about 150V, and changes by 4V from that (higher than 150V with 5 mA load current, and lower than 150V with 40 mA load current).
The B+ voltage that comes before the OA3 and OD3 is not regulated.
Suppose it is normally 350V, but changes from 340V to 360V because the power mains varies from 117VAC to 123VAC;
Or power mains variation of from 214VAC to 226VAC.
Subtract 75V (perhaps 72.5V or 77.5V with load variation) from a B+ of 340 to 360V, that does not regulate the voltage to the amplifier tube.
Subtract 150V (perhaps 147.5V or 152.5V with load variation) from a B+ of 340 to 360V, that does not regulate the voltage to the amplifier tube.
Those regulator tubes only regulate the voltage drop from B+, but does not regulate the final voltage, because B+ is unregulated.
Just my opinions.
As you have drawn the schematic . . .
Those regulator tubes provide a relatively constant voltage drop from whatever the B+ voltage is.
OA3 drops about 75V, and changes by 5V from that (higher than 75V with 5 mA load current, and lower than 75V with 40 mA load current).
OD3 drops about 150V, and changes by 4V from that (higher than 150V with 5 mA load current, and lower than 150V with 40 mA load current).
The B+ voltage that comes before the OA3 and OD3 is not regulated.
Suppose it is normally 350V, but changes from 340V to 360V because the power mains varies from 117VAC to 123VAC;
Or power mains variation of from 214VAC to 226VAC.
Subtract 75V (perhaps 72.5V or 77.5V with load variation) from a B+ of 340 to 360V, that does not regulate the voltage to the amplifier tube.
Subtract 150V (perhaps 147.5V or 152.5V with load variation) from a B+ of 340 to 360V, that does not regulate the voltage to the amplifier tube.
Those regulator tubes only regulate the voltage drop from B+, but does not regulate the final voltage, because B+ is unregulated.
Just my opinions.
Yes, I know. I'm not sure what the voltage will be after the 5U4 rectifier, maybe 320V. The corresponding voltage drops are indicated with a ~sign, given 320 as B+.
The designer actively seeks the use of electrons from the diode gap of the regulator tubes, and states that this has audible superiority over use of resistors or chokes. I agree the voltages are really not regulated this way, only the drops are.
Interesting statement. I'd actually like to build both versions to find out.
The designer actively seeks the use of electrons from the diode gap of the regulator tubes, and states that this has audible superiority over use of resistors or chokes. I agree the voltages are really not regulated this way, only the drops are.
Interesting statement. I'd actually like to build both versions to find out.
Solvt,
Using those gas tubes . . .
The OA3 and OD3. 40mA - 5mA = 35mA. 35mA/2 = 17.5mA. The design center of the gas tubes is 17.5mA + 5mA = 22.5mA.
With specified currents, the 75V ranges up to 5V versus load, and the 150V ranges up to 4V versus load.
Using a dropping resistor:
75V / 22.5mA requires a 3,333 Ohm resistor. A change of 17.5mA load would give a 58volt change.
150V / 22.5mA requires a 6,666 Ohm resistor. A change of 17.5mA load would give a 117volt change.
In order to be able to use resistors, instead of the OA3 and OD3, you would definitely have to use capacitors to ground to bypass the changes in currents to the resistors.
Conclusion:
Without the bypass caps across the resistors, the voltage from the OA3 and OD3 voltage would more stable.
Gas tubes by themselves; resistors with bypass caps to ground . . . either way will work well.
Using those gas tubes . . .
The OA3 and OD3. 40mA - 5mA = 35mA. 35mA/2 = 17.5mA. The design center of the gas tubes is 17.5mA + 5mA = 22.5mA.
With specified currents, the 75V ranges up to 5V versus load, and the 150V ranges up to 4V versus load.
Using a dropping resistor:
75V / 22.5mA requires a 3,333 Ohm resistor. A change of 17.5mA load would give a 58volt change.
150V / 22.5mA requires a 6,666 Ohm resistor. A change of 17.5mA load would give a 117volt change.
In order to be able to use resistors, instead of the OA3 and OD3, you would definitely have to use capacitors to ground to bypass the changes in currents to the resistors.
Conclusion:
Without the bypass caps across the resistors, the voltage from the OA3 and OD3 voltage would more stable.
Gas tubes by themselves; resistors with bypass caps to ground . . . either way will work well.
Is there no risk on relaxation oscillations in the 0D3 in the schematic of post #64 with 33 uF of capacitance shunting it?
From the attached article it seems to follow that the risk on relaxation oscillations is higher if the shunting capacitance is higher and/or the current is lower and/or the series resistance is lower. These numbers differ a bit between specimens of one tube type.
Based on the article I think that the current through the 0A3's will surely be high enough to not cause problems.
But will the current through the 0D3 be high enough to never cause oscillations? I estimate that current to be not much more than 4 mA when looking at the value of the plate resistors (47K). But I struggle with the effect of series resistance, and how to 'translate' that to the situation in the schematic in post #64.
From the attached article it seems to follow that the risk on relaxation oscillations is higher if the shunting capacitance is higher and/or the current is lower and/or the series resistance is lower. These numbers differ a bit between specimens of one tube type.
Based on the article I think that the current through the 0A3's will surely be high enough to not cause problems.
But will the current through the 0D3 be high enough to never cause oscillations? I estimate that current to be not much more than 4 mA when looking at the value of the plate resistors (47K). But I struggle with the effect of series resistance, and how to 'translate' that to the situation in the schematic in post #64.
Some designers will go to great lengths to eliminate having to use a bypass cap(s) across the cathode self bias resistor.
(Bypass caps to them are bad sounding).
Some designers in an effort to eliminate noise, and lower the high frequency impedance of an OA3 or an OD3 will use a bypass cap(s) across those gas tubes.
(Bypass caps to them are OK sounding).
Some designers replace the B+ voltage dropping series-connection dropping OA3 or OD3 and the bypass cap(s) across them.
Instead, those designers replace the OA3 or OD3 with a dropping resistor and . . . you guessed it . . . bypass cap(s) to ground.
(Bypass caps to them are OK sounding).
Is there any logic to this?
(Bypass caps to them are bad sounding).
Some designers in an effort to eliminate noise, and lower the high frequency impedance of an OA3 or an OD3 will use a bypass cap(s) across those gas tubes.
(Bypass caps to them are OK sounding).
Some designers replace the B+ voltage dropping series-connection dropping OA3 or OD3 and the bypass cap(s) across them.
Instead, those designers replace the OA3 or OD3 with a dropping resistor and . . . you guessed it . . . bypass cap(s) to ground.
(Bypass caps to them are OK sounding).
Is there any logic to this?
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Nice reference to a formerly classified(!) paper from capt. Woodyard from the US Naval explosives dept. in 1952! 
Another is this: https://hal-univ-tln.archives-ouvertes.fr/hal-01056923/document
Two comments on the use of the capacitors:
a) The rather wide variety of capacitanes in each capacitor battery (with "battery" I mean the three caps for each voltage regulator) will probably slow down possible oscillations in the circuit.
b) Maybe it would be beneficial to let the capacitors go from B+ to ground instead of in parallell with each regulator, providing a buffer of electrons with varying capacity and speed, as well as a filter from the ripple I guess is present on the secondary side of the 5U4 rectifier. More like the use of the capacitors in the schematic in post #62. But I think the interpretation from the Decware design log points to what is in the schematic in #64.
This is some of what makes engineering of audio equipment partly art, partly mathematics. Not all the science in sound reproduction is described / known, hence still heavily debated. Adding to the complexity that equipment / setups sound really different between rooms and relative the beholder - these discussions are hard to settle. And contribute to some of the buty of the art of this engineering.
Another is this: https://hal-univ-tln.archives-ouvertes.fr/hal-01056923/document
Two comments on the use of the capacitors:
a) The rather wide variety of capacitanes in each capacitor battery (with "battery" I mean the three caps for each voltage regulator) will probably slow down possible oscillations in the circuit.
b) Maybe it would be beneficial to let the capacitors go from B+ to ground instead of in parallell with each regulator, providing a buffer of electrons with varying capacity and speed, as well as a filter from the ripple I guess is present on the secondary side of the 5U4 rectifier. More like the use of the capacitors in the schematic in post #62. But I think the interpretation from the Decware design log points to what is in the schematic in #64.
This is some of what makes engineering of audio equipment partly art, partly mathematics. Not all the science in sound reproduction is described / known, hence still heavily debated. Adding to the complexity that equipment / setups sound really different between rooms and relative the beholder - these discussions are hard to settle. And contribute to some of the buty of the art of this engineering.
I am reminded of the 1970's published double-blindfolded A-B listening test.
A large number of solid state amplifiers, and a vacuum tube Futterman OTL amplifier were used.
There were not any statistical results that could show there was a significant difference in sound of all of them.
All the solid state amplifiers, and the Futterman amplifiers had two things in common:
1. All of them used Totem Pole output.
2. All of them used lots of Global Negative Feedback.
Of course that test has been discounted by many audio persons . . .
. . . But the fact remains that there has never been a similar test that was run, and published that I can find.
Nobody has taken the time, room, equipment, speakers, signal sources, audio knowledgeable people, etc. and tried to run
another double-blindfolded A-B listening test with solid state Totem Pole outputs and vacuum tube Totem Pole outputs and all of them with lots of Global Negative Feedback.
Just My Opinions
A large number of solid state amplifiers, and a vacuum tube Futterman OTL amplifier were used.
There were not any statistical results that could show there was a significant difference in sound of all of them.
All the solid state amplifiers, and the Futterman amplifiers had two things in common:
1. All of them used Totem Pole output.
2. All of them used lots of Global Negative Feedback.
Of course that test has been discounted by many audio persons . . .
. . . But the fact remains that there has never been a similar test that was run, and published that I can find.
Nobody has taken the time, room, equipment, speakers, signal sources, audio knowledgeable people, etc. and tried to run
another double-blindfolded A-B listening test with solid state Totem Pole outputs and vacuum tube Totem Pole outputs and all of them with lots of Global Negative Feedback.
Just My Opinions
as long as nothing burns, no one gets electrocuted, then all is fine with diy., DIY lets you get as crazy as you want, all within reason.....
gas regulator tubes are shunt devices, i have yet to try them as series pass devices, i have not yet figured out why i should...so until then, i will use mosfets instead for such applications...
gas regulator tubes are shunt devices, i have yet to try them as series pass devices, i have not yet figured out why i should...so until then, i will use mosfets instead for such applications...
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PLF200: I see in the OA3 data sheet (https://frank.pocnet.net/sheets/049/0/0A3.pdf) that it is not recommended to shunt the regulator with more than 0.1uF capacitance. Maybe the configuration below is more sensible then:
This still leaves the large 33uF as an electron buffer for all the regulators, but going to ground it does not directly shunt the regulators. Looking back to the Decware design log, the UFO25 design change introducing the voltage regulator tubes was supposed to include/add 7 caps and 9 poly film caps:
Rather than the two capacitors used in the power supplies of the SE84UFO and SE84UFO2, this uses a few more. The first cap comes off the rectifier tube just like the other amps but then the power supply is split into three separate filters, one for each tube. This adds 7 additional caps and nine additional poly film bypass caps. There was no option other than to spit it into three separate supplies due to the 30mA limit of the OA3 tube. And because the large gap beautifully slows things down, all of the caps have to be carefully bypassed to speed things back up. This stretch between speeds expands the transient playground to a very large window giving a more immersive sense of depth and complexity. The slow side of its personality creates unbelievable liquidity. The fast side of it's personality reveals stuff you had no idea was there, and that Zen duality creates an infinitely variable speed power supply that fills in the middle.
This might be interpreted as 2 of 9 caps in the power supply are poly film, or 7 electrolytic and 9 polyfilms.. Which I don't see how all those caps are going to be used.. I have drawn 7 caps as a part of the power supply for the tubes, after the initial large "old/normal" cap. Then there are 2 additional caps on the cathode side, but these have always been there in the old Zkit1 schematics as well. Not entirely sure how to interpret this..
This still leaves the large 33uF as an electron buffer for all the regulators, but going to ground it does not directly shunt the regulators. Looking back to the Decware design log, the UFO25 design change introducing the voltage regulator tubes was supposed to include/add 7 caps and 9 poly film caps:
Rather than the two capacitors used in the power supplies of the SE84UFO and SE84UFO2, this uses a few more. The first cap comes off the rectifier tube just like the other amps but then the power supply is split into three separate filters, one for each tube. This adds 7 additional caps and nine additional poly film bypass caps. There was no option other than to spit it into three separate supplies due to the 30mA limit of the OA3 tube. And because the large gap beautifully slows things down, all of the caps have to be carefully bypassed to speed things back up. This stretch between speeds expands the transient playground to a very large window giving a more immersive sense of depth and complexity. The slow side of its personality creates unbelievable liquidity. The fast side of it's personality reveals stuff you had no idea was there, and that Zen duality creates an infinitely variable speed power supply that fills in the middle.
This might be interpreted as 2 of 9 caps in the power supply are poly film, or 7 electrolytic and 9 polyfilms.. Which I don't see how all those caps are going to be used.. I have drawn 7 caps as a part of the power supply for the tubes, after the initial large "old/normal" cap. Then there are 2 additional caps on the cathode side, but these have always been there in the old Zkit1 schematics as well. Not entirely sure how to interpret this..
My guess is that there will be hum because the 'regulators' don't regulate in this series arrangement. The power stages only have 1 x 33 uF as buffer/smoothing.
Edit: Why are the suppressor grids of the 6P15P connected to the cathode through 0.1 uF capacitors? I think they should be connected straight to the cathode, so without the capacitors.
Edit: Why are the suppressor grids of the 6P15P connected to the cathode through 0.1 uF capacitors? I think they should be connected straight to the cathode, so without the capacitors.
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PFL200,
1. You have noticed the invention of Decware, the Hazen Mod.
It floats the Suppressor Grid (no DC return).
But it connects a capacitor from the suppressor grid to the cathode at AC (that has varying impedance versus frequency).
I will never even try to build and listen to the Hazen Mod.
Your Mileage May Vary . . . if you float the suppressor grid (or beam formers of a 6CA7, some are built that way).
2. Yes, that amplifier needs much more filtering before passing B+ to the voltage dropping devices: gas tube or a zener.
3. The OD3 does look pretty.
I used one on an amplifier; it was there for looks.
But when the power is switched off, it brings the B+ down to 150V.
1. You have noticed the invention of Decware, the Hazen Mod.
It floats the Suppressor Grid (no DC return).
But it connects a capacitor from the suppressor grid to the cathode at AC (that has varying impedance versus frequency).
I will never even try to build and listen to the Hazen Mod.
Your Mileage May Vary . . . if you float the suppressor grid (or beam formers of a 6CA7, some are built that way).
2. Yes, that amplifier needs much more filtering before passing B+ to the voltage dropping devices: gas tube or a zener.
3. The OD3 does look pretty.
I used one on an amplifier; it was there for looks.
But when the power is switched off, it brings the B+ down to 150V.
Never heard of it before. Google directed me to this: https://www.decware.com/newsite/paper146.html
I get a bit irritated when reading things in it like: "Because the change is for the better, you can only assume that dissloged electrons are probably a bad thing for clarity and dimensionality.".
At best it doesn't mess up things much in triode mode. Like you, I will never even try it. Why not connect g3 to the plate+g2 if one is 'suspicious of a wire between g3 and the cathode'?
I get a bit irritated when reading things in it like: "Because the change is for the better, you can only assume that dissloged electrons are probably a bad thing for clarity and dimensionality.".
At best it doesn't mess up things much in triode mode. Like you, I will never even try it. Why not connect g3 to the plate+g2 if one is 'suspicious of a wire between g3 and the cathode'?
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the final version of my decware zen clone now with diodes instead of 5ar4 ,first 2 caps 47uf rubycon +0,5uf pio last cap 10uf 630v pio ,bias 6n23p switchable from 2 leds to resistor 960 ohm it ,s a nice relax sounding litlle amp ,with enough power to drive my philips ad5200m7 in a homemade tannoy grf cabinet
