A lot of diodes out there and I’m a little bit 
. There are fast recovery, ultra fast, schotky, e.t.c.
I have seen the MUR ones, HFA, BYV and some other I don’t remember.
I know that many of you out there had tried some of them and have an opinion upon this topic.
Which to choose?
Over here you will ask me, for how many Volts and how much current.
I’d like to put them in the PSU of my P-P amp. One PSU for two 6L6 P-P channels (L+R). I’ll use HT at 420V and about 50-60mA idle current.
Mention that secondary will be with CT so, not bridge over here.
. There are fast recovery, ultra fast, schotky, e.t.c. I have seen the MUR ones, HFA, BYV and some other I don’t remember.
I know that many of you out there had tried some of them and have an opinion upon this topic.
Which to choose?
Over here you will ask me, for how many Volts and how much current.
I’d like to put them in the PSU of my P-P amp. One PSU for two 6L6 P-P channels (L+R). I’ll use HT at 420V and about 50-60mA idle current.
Mention that secondary will be with CT so, not bridge over here.
Hi,
Basically you want the diodes to be as "quiet" as possible.
As you may know solid state diodes_at least most of them do_exhibit commutation peaks that can cause reverse voltage peaks and create nasty RFI noise.
The better types_for audio use_ are the ones commonly known as "soft recovery" types or better still Schottky diodes.
Unfortunately for high voltages the new silicium carbide Schottky diodes are just hitting the shops and are relatively expensive.
The only manufacturer of such diodes I know of is U.S. based Cree.
By using snubber networks across each individual diode, ordinary diode types can be made pretty quiet but the values of the RC network components are best determined by experimenting while looking at an o-scope's output.
All in all, a tube rectifier is still the better way IMO. A damper diode is reported to give excellent results as do the hybrid rectifiers using a pair of SS diodes and a FW tube rectifier configured as a Graetz bridge.
Be ware that SS diode cause considerably less voltage drop than any tube diode would.
Cheers,
Basically you want the diodes to be as "quiet" as possible.
As you may know solid state diodes_at least most of them do_exhibit commutation peaks that can cause reverse voltage peaks and create nasty RFI noise.
The better types_for audio use_ are the ones commonly known as "soft recovery" types or better still Schottky diodes.
Unfortunately for high voltages the new silicium carbide Schottky diodes are just hitting the shops and are relatively expensive.
The only manufacturer of such diodes I know of is U.S. based Cree.
By using snubber networks across each individual diode, ordinary diode types can be made pretty quiet but the values of the RC network components are best determined by experimenting while looking at an o-scope's output.
All in all, a tube rectifier is still the better way IMO. A damper diode is reported to give excellent results as do the hybrid rectifiers using a pair of SS diodes and a FW tube rectifier configured as a Graetz bridge.
Be ware that SS diode cause considerably less voltage drop than any tube diode would.
Cheers,
resident said:A lot of diodes out there and I’m a little bit
I have seen the MUR ones, HFA, BYV and some other I don’t remember.
Well, application specific of course. High speed diodes (including schottky) are only needed in high speed applications such as switching power supplies. Normal recovery and/or glass passivated (more durable, AFAIK) types are suitable for 50/60Hz operation.
All diodes posess a recovery time, which means it keeps conducting after the terminal voltage reverses. (Normal recovery is on the order of 1uS, compared to the 8.33mS half cycle of 60Hz AC. Schottkys are down around 5nS!) This pulls current back out of the filter capacitor, causing a momentary current spike. This most commonly manifests itself as noise coupled through the power transformer to the heater winding - any amplifier of mine which had diode noise was quieted right down with proper heater practices.
Er, stereo PP 6L6's? That's going to draw four times what you claim (around 250mA).
Tim
I have tried a hybrid Graetz bridge, with MUR4100E SS diodes in the negative half and 6D22S TV thermionic damper diodes in the positive half. This arrangement is supposed to be just as quiet as an all-thermionic bridge.
I then tried an all-SS bridge, to get a bit more voltage. I didn't notice any increase in noise as a result. However, I'm using smoothing chokes and 0.1uF capacitors in parallel with the normal electrolytic smoothing capacitors, which I suppose must help in getting rid of any noise from the diodes.
I then tried an all-SS bridge, to get a bit more voltage. I didn't notice any increase in noise as a result. However, I'm using smoothing chokes and 0.1uF capacitors in parallel with the normal electrolytic smoothing capacitors, which I suppose must help in getting rid of any noise from the diodes.
Diode noise is not something you are likely to hear in isolation. It does, however, change the sonic character of the amp in a very profound way no matter how many chokes you have in the PS and how much you've tweaked the heaters.
I haven't tried schottkys but all other SS rectifiers i've tried sounded as crap.
I see that many of you prefer diode rectifiers.
I have done the holes so, I don't know if I can put a diode rectifier.
If I can, which do you suggest?Remember that I'm using only one PSU for two channels.
@analog sa
Many people prefer SS amps!Many people prefer SE amps and many P-P.Other prefer horns and other normal ones.
Who is wrong????????????????????????????????????????
@sch3mat1c
I have done the holes so, I don't know if I can put a diode rectifier.
If I can, which do you suggest?Remember that I'm using only one PSU for two channels.
Yes I know.I'm thinking to use a diode up to 0.5A.
@analog sa
Don't be so sure about this.Many people prefer SS diodes.What are they?Stupid?
Many people prefer SS amps!Many people prefer SE amps and many P-P.Other prefer horns and other normal ones.
Who is wrong????????????????????????????????????????
@sch3mat1c
With proper heater practices?What do you mean?
You'd be amazed as how many are actually stupid
. Or deaf.Commercial equipment understandably prefers SS; if i were a manufacturer i wouldn't hesitate using SS too - cheap, easy, less PS troubles, reliabilty, good bass; and how many of the potential customers can hear anyway?
The issue with the bass is btw a real one. None of the vacuum rectifiers i've tried produce particularly good bass. If you want really high quality bass you need MERCURY. I don't think any manufacturer would ever dream of using such devices in a commercial venture. And most DIYers with children, pets or wives may think twice.
I agree with you!
Mercury?Mmmm...This is brand of tube rectifier?Which type of tube?
ha ha LOL!Yes, how many can hear anyway?I have visit many that listen from crap systems and I can't believe that they like them.I'm not an expert but I have listen good systems(most of them are diy) and I'm trying to upgrade mine ,too.
Anyway thanks that you are helping me and sorry if I reply to you a little bit awfull.
resident said:
Well, you connect heaters to a 6.3V (or whatever) winding... you might ground one side of that winding. Now it can't move up and down and couple noise to the cathodes (primarily electrostatic, i.e. the capacitance between heater and the cathode around it). That leaves one side wild however, putting an average 3.15VAC between the heater and cathode. So you might ground a center tap of the heater instead (most often done with a pair of resistors, or a variable resistor, known as a "hum balance"). That balances the AC voltage on the heater, nulling the voltage coupled to the cathode.
Better still, however, is elevating the heaters with a DC bias, above all the cathodes (within limits). Say you have a 6C4 with 2V cathode bias and a 6V6 with 15V cathode bias, 30V heater bias would be good. (No more than 70V or so, as that would exceed the 6C4's H-K rating.) This reduces leakage because the heater acts like a filament cathode (I mean, it's hot tungsten, right?) and the inside of the cathode sleeve acts like the plate of a small diode. Putting the heater above the cathode voltage-wise "turns off" the diode.
A combination of these, a voltage divider with capacitor bypassing to ground, is best, and I have had good success with it.
DC heaters are another can of worms, but suffice it to say it isn't necessary in all but the most unruly tubes or high gain stages.
Back on topic, you'd use a mercury rectifier such as #83 or (if you have some real power to rectify) 866. Those are the only types off the top of my head. Note that mercury tubes require RF hash chokes at a minimum, and preferably a good faraday cage to supress all the noise -- they switch orders of magnitude worse than any silicon diode.
Tim
Yup. I've heard this before. Another great example of practice not following theory. Or maybe whatever noise they generate is completely irrelevant to audio? Or due to age related HF hearing loss (14.5kHz) i am simply not bothered? Whatever.
Still, mercury somehow helps making music in a way that no hexfred can ever dream. Tonality, dynamics, bass - done right.
Yes, using them is a bother; they require compulsory preheating; they are not easy to parallel; they really suck current from the heater ps. Not to mention the ghastly purple shine... bit it's all worth it.
Hmmm
I thing I’ll try those tubes.
What are these RF hash chokes?
Now I’ll use one of the best SS diodes, HFA08TB60.
A lot claim to be the best ones. And I’ll try to find a mercury tube to do a test btw those two.
I love tubes and I’d like to see those SS diodes to sound as crap at the test with the mercury tubes.
These tubes are a little bit rare! I have seen some 83 somewhere but they were expensive.
I’ll build this amp with SS diodes, I already have all the components and now I’m placing them together! Hope until Wednesday will be ready.
But mercury will be on my mind!
One question out of our discussion,
Where is the best place to put the stand by switch?
At the CT of the power transformer (SPST)?
Between windings and diodes (DPDT)?
Between diodes and first cap of p-filter?
Or after the p-filter?
I thing I’ll try those tubes.
What are these RF hash chokes?
Now I’ll use one of the best SS diodes, HFA08TB60.
A lot claim to be the best ones. And I’ll try to find a mercury tube to do a test btw those two.
I love tubes and I’d like to see those SS diodes to sound as crap at the test with the mercury tubes.
These tubes are a little bit rare! I have seen some 83 somewhere but they were expensive.
I’ll build this amp with SS diodes, I already have all the components and now I’m placing them together! Hope until Wednesday will be ready.
But mercury will be on my mind!
One question out of our discussion,
Where is the best place to put the stand by switch?
At the CT of the power transformer (SPST)?
Between windings and diodes (DPDT)?
Between diodes and first cap of p-filter?
Or after the p-filter?
If you're really mad enough to try the 83 (you know what mad as a hatter means and why, don't you?) make sure you have a spare source of 5v@3A and connect the switch to the CT ground return. The 83 absolutely has to warm up for at least 30 sec before the high voltage hits the plates.
To fully enjoy the benefits of low impedance rectifiers you may wish to choose transformers and chokes with as low dc resistance as possible. Luckily Lundahl make some PS chokes with extremely low resistance but the transformers have to be custom wound. I can attest to the benefits of low DC res chokes but still have to try some truly low resistance transformers. 3-4 ohms resistance on the secondary seems to be the goal.
Hi,
I have equipment that uses 83's. The manual recommends a much longer warm up time to allow the mercury to evapourate fully to support the current flow. I belive the figure was around 20 min. before applying plate voltage and a load. This is test equipment.
Yes, RF chokes are needed. As is a shield around the tube (well ventillated. I am sure the tubes are in use without these precautions, but they will not last as long or you will pick up the hash. The forward voltage drop will be around 15V and reasonably constant with load.
I use silicon diodes in anything new. The voltage drop is less and more consistant. The noise is much less and no lost power to the heater. Include a series resistance to greatly reduce switching noise.
-Chris
I have equipment that uses 83's. The manual recommends a much longer warm up time to allow the mercury to evapourate fully to support the current flow. I belive the figure was around 20 min. before applying plate voltage and a load. This is test equipment.
Yes, RF chokes are needed. As is a shield around the tube (well ventillated. I am sure the tubes are in use without these precautions, but they will not last as long or you will pick up the hash. The forward voltage drop will be around 15V and reasonably constant with load.
I use silicon diodes in anything new. The voltage drop is less and more consistant. The noise is much less and no lost power to the heater. Include a series resistance to greatly reduce switching noise.
-Chris
YEs, switch in CT loop is fine for SS as well.
Neither myself, not anyone else i know have ever experienced problems with 83 noise. I don't claim they don't generate noise; it just appears to be a non-issue. Small chokes connected in series with the plates appear to be harmless but resistors will destroy the advantages of low forward resistance.
Warm up: the 20 or so minutes is recommended as a one off conditioning after the tubes have been in storage. In normal operation 30 sec is sufficient. There are quite a few tube testers powered by an 83 with no delay between heaters and plate voltage and they seem to last.
Neither myself, not anyone else i know have ever experienced problems with 83 noise. I don't claim they don't generate noise; it just appears to be a non-issue. Small chokes connected in series with the plates appear to be harmless but resistors will destroy the advantages of low forward resistance.
Warm up: the 20 or so minutes is recommended as a one off conditioning after the tubes have been in storage. In normal operation 30 sec is sufficient. There are quite a few tube testers powered by an 83 with no delay between heaters and plate voltage and they seem to last.
Hi analog_sa,
If you use a 'scope on the rectified output, you will see "hash" on the waveform. This may interfere with a tuner. Resistance in series with silicon diodes removes the "spike" from the output. Given the resistance and voltage drop of tube rectifiers, this is not an issue at all. You are still way ahead with the "sand".
No, I don't replace existing tube rectifiers with solid state units unless I have a good reason to do so. But if I am designing something new .... silicon diodes. The higher B+ allows me to use a voltage regulator for really low noise (SS - sorry) B+ lines for preamp stages.
My tube tester recommends a 20 min warm up every time. I'll follow this recommendation, it may only need 5 - 10 min.
-Chris
If you use a 'scope on the rectified output, you will see "hash" on the waveform. This may interfere with a tuner. Resistance in series with silicon diodes removes the "spike" from the output. Given the resistance and voltage drop of tube rectifiers, this is not an issue at all. You are still way ahead with the "sand".
No, I don't replace existing tube rectifiers with solid state units unless I have a good reason to do so. But if I am designing something new .... silicon diodes. The higher B+ allows me to use a voltage regulator for really low noise (SS - sorry) B+ lines for preamp stages.
My tube tester recommends a 20 min warm up every time. I'll follow this recommendation, it may only need 5 - 10 min.
-Chris
Hi,
What you're doing with the series resistance and diodes is exactly what's done with solid state replacements for tube rectifiers such as the 5AR4. Except that the series resistance is calculated to give the same drop as the real tube rectifier.
However, from my experience I noticed the following:
A series resistor won't do away with the fact that the diodes will still spit back a nasty spike and considerable amounts of RF hash into the mains.
It is not very effective in doing away with all the hash going into the circuit either and doesn't give you the nice slow start most tube rectifier do.
Last but not least: no matter how much snubbing applied, it still doesn't make it sound the way a true tube rectifier does....
Not even the better SiC Cree diodes. Much to my dismay, BTW.
The best compromise I ever tried so far is the hybrid rectifier scheme which seems to combine the best of both worlds.
Note: I never tried mercury vapours as every engineer I ever had working for me always warned against the RF noise problem and of course the longish pre-heating protocol.
I still have half a dozen of tubetesters employing 83s among other rectifiers and they all have been working reliably for about twenty years with just a few minutes warm-up.
Cheers,
What you're doing with the series resistance and diodes is exactly what's done with solid state replacements for tube rectifiers such as the 5AR4. Except that the series resistance is calculated to give the same drop as the real tube rectifier.
However, from my experience I noticed the following:
A series resistor won't do away with the fact that the diodes will still spit back a nasty spike and considerable amounts of RF hash into the mains.
It is not very effective in doing away with all the hash going into the circuit either and doesn't give you the nice slow start most tube rectifier do.
Last but not least: no matter how much snubbing applied, it still doesn't make it sound the way a true tube rectifier does....
Not even the better SiC Cree diodes. Much to my dismay, BTW.
The best compromise I ever tried so far is the hybrid rectifier scheme which seems to combine the best of both worlds.
Note: I never tried mercury vapours as every engineer I ever had working for me always warned against the RF noise problem and of course the longish pre-heating protocol.
I still have half a dozen of tubetesters employing 83s among other rectifiers and they all have been working reliably for about twenty years with just a few minutes warm-up.
Cheers,
Hi Frank,
Quite correct in that there is no soft start. I put the series R in the anodes. I guess you could put some small caps across the diodes to slow down the switching speed too. That should reduce the amount of hash into the mains. Basically, you only need to slow down dv/dt to kill the hash. (snubbing).
For preamps, all you need to do is ramp up the reg output. You can not hear the rectifier type at all doing this. Unless you have solid state diodes that put HF hash on the DC which may pass by a regulator.
The reason your 83's may last is that you aren't drawing near the max current in this situation. In a power supply for an amp, this isn't the case. The mercury must be fully (or nearly so) vapourised to handle all the current at higher loads. Damage occurs when the current flow can not be supported by the ionized gas.
-Chris
Quite correct in that there is no soft start. I put the series R in the anodes. I guess you could put some small caps across the diodes to slow down the switching speed too. That should reduce the amount of hash into the mains. Basically, you only need to slow down dv/dt to kill the hash. (snubbing).
For preamps, all you need to do is ramp up the reg output. You can not hear the rectifier type at all doing this. Unless you have solid state diodes that put HF hash on the DC which may pass by a regulator.
The reason your 83's may last is that you aren't drawing near the max current in this situation. In a power supply for an amp, this isn't the case. The mercury must be fully (or nearly so) vapourised to handle all the current at higher loads. Damage occurs when the current flow can not be supported by the ionized gas.
-Chris
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.