I've used the 6CA4/EZ81 9-pin tube rectifier with great success. It is cheap, readily available, in current manufacture, and works great.
However, I'm working on a project needing something physically smaller that generates a bit less heat (it will be in a non-ventilated enclosure). The EZ81 filament consumes 1A at 6.3V. Compare that to a 12AX7, which consumes only 0.3A at 6.3V. So a valve rectifier approximately the same size as a 12A*7 valve would be perfect.
I only need 20-40mA. Does anyone have recommendations for a small, cheap, and available rectifier valve?
However, I'm working on a project needing something physically smaller that generates a bit less heat (it will be in a non-ventilated enclosure). The EZ81 filament consumes 1A at 6.3V. Compare that to a 12AX7, which consumes only 0.3A at 6.3V. So a valve rectifier approximately the same size as a 12A*7 valve would be perfect.
I only need 20-40mA. Does anyone have recommendations for a small, cheap, and available rectifier valve?
If it's in an unventilated box, that likely means you can't see the nice glow of its heater, and thus no eye candy, so you might as well go SS for the rectifier. 
I wouldn't worry about cathode stripping, that's only an issue in high powered equipment like 50KW radio station transmitters or radar installations.
I wouldn't worry about cathode stripping, that's only an issue in high powered equipment like 50KW radio station transmitters or radar installations.
You can squeeze 20 mA. out of a 6AL5. As the data sheet shows, PIV is low at 330 V. So, use either a hybrid Grätz bridge or the arrangement I call "cockeyed bridge", depending on the power trafo you employ, in the setup.
I agree with the previous remarks about allowing for some ventilation. A few strategically placed holes will provide enough air flow for cool running types, like the 12AX7 and the 6AL5.
I've built with both. Without a doubt, valve rectification exhibits superior sonic performance. I surmise the P-N junction commutation noise of the solid-state diodes contain sufficient high-frequency components to affect performance. My solid-state power supplies have RC snubber networks around the diodes, common-mode RF chokes, MOSFET capacitance multipliers, 4-layer circuit boards with shield and ground planes, meticulous analog layout to control noise, and other complications.
My valve-rectified power supplies have a valve, a capacitor/choke "pi" filter, and sound much better, even with sloppy layout and no shielding.
I'm using a split secondary "full wave" transformer.
Me, too. I was being a little extreme. I'll drill some holes.
I also saw the Chinese 6Z4. Odd tube, I only found a datasheet in Chinese. It appears the 6X4 is similar to the EZ90. May be a little large, about a half-inch taller than the small Novel 9-pin types.
Well, wasn't this obvious? A 12AU7 would probably do the trick. Thanks!
If "noise" (your term, not mine) from your power rectifier is getting into your audio stream, then you have very inadequate power supply filtering. Using firebottles for simple power rectification is environmentally irresponsible and technically unsupportable in this era of resource conservation and "global warming".
That comment is really more than a little over the top, admittedly the tube rectifier has the additional filament draw, but have you actually looked at typical PF in the tube rectifier based circuit versus a solid state rectifier? (Usually a good deal worse with ss and PF correction is not very practical at a diy level. ) At these current levels the tube rectifier is not a particular wastrel.
If you read the OP comments carefully you will see that he went to great pains to control noise from the ss rectifiers and was not satisfied with the results. A valid reason IMO for the choice he is making.
The bigger picture is this device probably consumes a miniscule amount of power and contributes insignificantly to global warming given its actual power consumption and the number of hours it will be in use.
IMHO Larger areas of concern should be your car, HVAC efficiency, lighting, cooking and your computer(s) and HDTV. Let's focus on things that actually can make a difference rather than criticizing someone for their rectifier preferences.
I see this is your very first post here, welcome to diyaudio..
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The person who is comparing a SS rectified circuit with capacitance multiplier and rc stages to a Valve with LC is been grossly unfair to the solid state. A choke filter will kill almost all HF noise from the rectifiers and intrinsically has a slightly rolled off top end - ie almost all noise components which will create objectionable IM distortion.
The SS set up has no such benefits apart from a small RF choke and a capacitance multiplier which has one of the grossest sonic signiture of any form of regulation.
I have successfully used SS rectifier (soft recovery) by placing some resistance in series to slow them down. Suitably snubbered I would be very surprised if you could hear any difference with this setup, and a valve rectifier.
Stick your valve infront of the CLC and report back with some relevant results.
Shoog
The SS set up has no such benefits apart from a small RF choke and a capacitance multiplier which has one of the grossest sonic signiture of any form of regulation.
I have successfully used SS rectifier (soft recovery) by placing some resistance in series to slow them down. Suitably snubbered I would be very surprised if you could hear any difference with this setup, and a valve rectifier.
Stick your valve infront of the CLC and report back with some relevant results.
Shoog
I have a 100 Ohm resistor in series with the SS diodes for this purpose. The resistor is then connected to a CLC network, with the L being a common-mode RF choke. I've also tried large chokes (i.e. 5H) in standard CLC configuration. The diodes are snubbed with RC networks (each diode has 110 Ohm in series with 0.068uF, calculated by the frequency characteristics of the commutation). The performance using various combinations was inferior to my valve rectified setup.
After extensive listening, I added the capacitance multiplier MOSFET, followed by 22uF of high-quality film capacitors. On the final output, I also tried the 5H choke. I remain unsatisfied with the SS setup, although the total noise (ripple + noise) on my 300VDC is around 2.5mV (measured with oscilloscope). I can still see spikes every 120Hz where the diode commutation noise is sneaking through. Obviously, the measured level is incredibly low, so my objections must be caused by radiated emissions.
The problem with using big chokes on SS power supplies is the RF commutation noise from the diodes traverses the windings of the inductor via the wire insulation (dielectric) from winding-to-winding. Only an RF choke, which is designed to prevent traversal, will satisfy the requirements. I measured significant energy traversing the 5H choke.
Another problem is the commutation noise and poor power factor radiates from the power transformer. The RF energy jumps easily across the power transformer's windings, and appears on the filament windings. I have measured this using an oscilloscope on the filament winding.
I have professional expertise in designing power electronics, analog circuits, and filters, especially high-sensitivity input circuits to analog-to-digital converters. This demands careful layouts, ground planes, shielding, bypassing, and very clean voltage references, especially demanding in the automotive environment.
The SS power supplies have been overall troublesome, whereas the valve rectification remains satisfying. My experience with building, tweaking, and listening to various power supplies has given me hands-on personal knowledge of the merits.
Therefore, so is the output stage bias current, driver stage bias current, anything that Nelson Pass designs, all single-ended amplifiers, the energy consumed by the DIYAudio computer server, etc. I would argue your computer consumes more energy in a day than the filament for my EZ81 rectifier (1A at 6.3V) consumes in a year (it only operates a few hours a day, and only on days I use it).
Not enough current. Looks like the EZ80 or EZ81 will have to do. Too bad nobody made a half-height EZ81/6CA4, because that's what I'm looking for.
I once bought a piece of hermetically sealed military equipment which was powered by a totally enclosed valve circuit including a 6X4 rectifier, so I don't think heat is an issue. 6X4s are narrower (7-pin) and shorter than ECC81s and use 600 mA for the heater so they sound as though they might fit your bill.
Kashmire,
Have you ever tried high PIV Schottky diodes? With their "noiseless" nature, they seem tailor made for your project. Zero heater power and zero switching noise can't be bad, based on what you have described.
You are correct about the capacitance associated with the many turns of wire in a large valued choke being a shunt at RF. The way you deal with that is by inserting a "hash" filter between the 1st filter cap. and the remainder of the PSU filter. The "hash" filter is a LC section made from a high current RF choke and a 1000 pF. mica or NPO ceramic capacitor. The LC section made from RF parts kills 2 types of "crud": PN junction diode switching noise and high order ripple overtone energy associated with large valued cap. I/P filters.
BTW, search the archives here and at AA for "cockeyed bridge", which is a technique for using FWCT power "iron" and hybrid rectification. Hybrid, in this case, means PN junction diodes in combination with either Schottky or vacuum diodes. A pair of 6AL5s draw 600 mA. of heater current and the 7 pin mini bottle is quite small.
Have you ever tried high PIV Schottky diodes? With their "noiseless" nature, they seem tailor made for your project. Zero heater power and zero switching noise can't be bad, based on what you have described.
You are correct about the capacitance associated with the many turns of wire in a large valued choke being a shunt at RF. The way you deal with that is by inserting a "hash" filter between the 1st filter cap. and the remainder of the PSU filter. The "hash" filter is a LC section made from a high current RF choke and a 1000 pF. mica or NPO ceramic capacitor. The LC section made from RF parts kills 2 types of "crud": PN junction diode switching noise and high order ripple overtone energy associated with large valued cap. I/P filters.
BTW, search the archives here and at AA for "cockeyed bridge", which is a technique for using FWCT power "iron" and hybrid rectification. Hybrid, in this case, means PN junction diodes in combination with either Schottky or vacuum diodes. A pair of 6AL5s draw 600 mA. of heater current and the 7 pin mini bottle is quite small.
Claiming that SS rectifiers create "noise" is "over the top". Claiming that PF is a "factor" in a full wave rectifier is "over the top".
Hearing power supply noise from ANY real cause is simply a symptom of inadequate filtering. Of course no amount of filtering can eliminate imaginary noise, so I can see the problem here.
Yes, my remarks about wasting power (both the power wasted by the heater/filament and that wasted by the inefficiency of any tube rectifier) was tongue-in-cheek. Note, however that millions of
are being spent on making cell phone chargers draw less idle current when not charging. You can win gold stars for shaving microamps off the power draw.If you can cite a valid double-blind experiment that shows that listeners can actually hear the difference between SS vs tube/valve rectifiers in the power supply, I will think about reconsidering my brash judgement. Else you can put me down as a solid disbeliever.
Perhaps he sould consider a big bank of batteries in the basement.
Richard, may I beg to differ. I doubt that anyone has bothered to do a valid DBT, but they don't really have to. A tube rectifier will give measurably worse regulation (higher series resistance) and is often used in guitar amps just for that reason. Switching noise from conventional solid state diodes is easily seen to add noise to amplifiers, well above conventional thresholds of audibility, especially when the grounding is not all it should be. With tubes, the noise from SS diodes on the high voltage supply is commonly coupled through the heater windings on the same transformer to the tube's cathode- this is an effect I've seen, measured, and heard myself.
Now, in a well-designed amp, this is not an issue- diodes can be snubbed or fast-recovery rectifiers used (UF4007 instead of 1N4007, for example) and at minimal cost. Separate heater transformers may be used. And most important, good grounding practice can avoid these issues, allowing one to enjoy the efficiency and better regulation of SS diodes without the switching noise.
Doubt that this is real? Break out a scope or (better yet) a spectrum analyzer and see for yourself.
Now, in a well-designed amp, this is not an issue- diodes can be snubbed or fast-recovery rectifiers used (UF4007 instead of 1N4007, for example) and at minimal cost. Separate heater transformers may be used. And most important, good grounding practice can avoid these issues, allowing one to enjoy the efficiency and better regulation of SS diodes without the switching noise.
Doubt that this is real? Break out a scope or (better yet) a spectrum analyzer and see for yourself.
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