Hi All, I am trying to understand why in RH84 amp by Mr Kitic vast majority of builders employ tube based rectifier?
Why not to use modern fast Schottky diodes + MOSFET based precise voltage stabilizator?
Pros of my way of thinking would be:
1.dead silent power supply.
2. voltage stability independently from mains voltage swings
Please give me cons??.....
Why not to use modern fast Schottky diodes + MOSFET based precise voltage stabilizator?
Pros of my way of thinking would be:
1.dead silent power supply.
2. voltage stability independently from mains voltage swings
Please give me cons??.....
But that’d be one less firebottle to bask in the glorious light of. 🙂
Been a while since I enjoyed my dalliance with tubed amps, and I fondly remember trying to convince myself of the subtle or dramatic changes in sonic signature by swapping out rectifier types.
I think we ran EZ81 in our RH84 monoblocks; Dave, does that sound right?
Been a while since I enjoyed my dalliance with tubed amps, and I fondly remember trying to convince myself of the subtle or dramatic changes in sonic signature by swapping out rectifier types.
I think we ran EZ81 in our RH84 monoblocks; Dave, does that sound right?
wlodek3055,
Perhaps using a tube rectifier results in a power supply that has more "voltage sag", and that can also add something to the overall sonic signature (and is preferred by some).
Perhaps using a tube rectifier results in a power supply that has more "voltage sag", and that can also add something to the overall sonic signature (and is preferred by some).
This is one of those subjective thingies that everyone has an opinion on, and it's really hard to determine who's right.
It's pretty well accepted that it's a bad idea to put HV on the plate of a tube before it can conduct that HV, before its heater has warmed up enough to allow current to flow from plate to cathode. So we have the option of soft start circuitry to delay the application of HV to the power tubes.
A tube rectifier will naturally provide that delay because it won't produce high voltage until it heats up. That's good for all the tubes. But a tube-rectified power supply is much more expensive than the bridge rectified supply. Does that extra cost exceed the cost incurred by applying that HV to your power tubes when they are cold? That's your $64,000 question.
Have fun
w
It's pretty well accepted that it's a bad idea to put HV on the plate of a tube before it can conduct that HV, before its heater has warmed up enough to allow current to flow from plate to cathode. So we have the option of soft start circuitry to delay the application of HV to the power tubes.
A tube rectifier will naturally provide that delay because it won't produce high voltage until it heats up. That's good for all the tubes. But a tube-rectified power supply is much more expensive than the bridge rectified supply. Does that extra cost exceed the cost incurred by applying that HV to your power tubes when they are cold? That's your $64,000 question.
Have fun
w
I see. Let's dig little deeper. Let's assume (this is actual status) I have delayed HV "ON" function + slow rise of voltage, in my stabilized power supply. So another issue gone... Still can't see "sonic" benefits. Some say that choke inductance is better "peak" current reservoair than capacitor. I can agree, BUT here we have amp that is operating in class A - so max current is drawn in idle. I don't buy that. Others say that vacuum diode hav shorter switch time - compared to fast Schottky diodes with time roud 18ns... again - don't buy that. What else could be an argument to go for vaccum rectifier? I am not trying to provoke or negate potential benefits. Just want to see rational behind, as vacuum rectifier is way more complex from my perspective and more expansive - so if I decide to do it - must be well justified.
Excrpt when you use a directly heated rectifier, in which case the delay is minimal.
In any case and regardless of whether a delay is good or bad, the burden is on the rectifier tube now ...
I am not so sure about that. Tubes have maximum characteristics for voltage limits on their anodes when cold. I think the scenario that has to be avoided is a hot output tube with full potential on the anode, and insufficient bias. So a bit of a delay allows voltages to settle before B+ is applied. But it can depend on the circuit. If the tubes have cathode bias then there is no big deal, and lots of consumer tube products worked without tube rectifiers.
Even so, I like to fit inrush current limiters on the amps I build myself. They absorb some of the peaks that would be created at the sharp spike after powering on.
From the OP's question, I think it is personal preference. A silicon bridge or a tube rectifier (and transformer with a CT secondary). I have used semiconductors in the last 2 amps I built.
OK, let me put question other way round - to experiance of those who build solid state AND tube rectifiers - is it any way to HEAR difference between them?? We speak about SINGLE ENDED calss A tube amp => current is drawn on max value in idle. Let's leave aside other considerations. Just SONIC differance.
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How complex and costly is the PS supply you built for this..? The circuit for a delayed ON and a ''slow'' rise of the input voltage isn't usually a simple construct. More design time, construction time and parts acquisition expense... Is the slow rise time @10 - 15 seconds?
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I built RH84 amp and initially not having a rectifier tube, I used a diode bridge with a resistor for the right voltage. Later I used GZ34 but I did not notice big audio differences...but with the tube it is very nice!
A damper diode has a relatively long soft start.
A 5AR4 has a relatively short soft start.
A 5Y3 has a relatively quick start.
The relative mass of the filament/cathode that creates the cloud of electrons, versus the volts x amps to heat them, is the main function that controls the length of time to warm up.
There are some Radar Rectifier/Damper diodes that take a full 2 minutes to warm up.
(and, they take just as long to cool, the tube must be protected from a Hot Start).
Design considerations about a cold amplifier at Power-on is one thing.
Design considerations about a Hot Start is much more complicated, and requires intelligent design.
Hot Start . . . when the amplifier is all warmed up, and the power goes down briefly, and comes back on, while all the tubes are still warm.
In addition to the on-off, on-off, on power; during a Hot Start there are often transient voltages that exceed the normal power mains voltages. OUCH!
I always use Solid State Diodes, and a center tapped full wave circuit.
Just the power transformers I have, and my choice of rectifiers.
A poorly designed Tube rectifier circuit is worse than a well designed Solid State rectifier circuit.
And, the reverse is also true:
A poorly designed Solid State rectifier circuit is worse than a well designed Tube rectifier circuit . . .
Attention to design details is needed (not just the rectifier circuit; but also all of the amplifier stages).
If reliability was only a function of good or bad luck, then I am going to Las Vegas (my tube amplifiers are reliable, Lucy me?).
YRMV (Your Reliability May Vary).
You can not enjoy listening to a dead amplifier.
Have Fun designing, building, and listening!
A 5AR4 has a relatively short soft start.
A 5Y3 has a relatively quick start.
The relative mass of the filament/cathode that creates the cloud of electrons, versus the volts x amps to heat them, is the main function that controls the length of time to warm up.
There are some Radar Rectifier/Damper diodes that take a full 2 minutes to warm up.
(and, they take just as long to cool, the tube must be protected from a Hot Start).
Design considerations about a cold amplifier at Power-on is one thing.
Design considerations about a Hot Start is much more complicated, and requires intelligent design.
Hot Start . . . when the amplifier is all warmed up, and the power goes down briefly, and comes back on, while all the tubes are still warm.
In addition to the on-off, on-off, on power; during a Hot Start there are often transient voltages that exceed the normal power mains voltages. OUCH!
I always use Solid State Diodes, and a center tapped full wave circuit.
Just the power transformers I have, and my choice of rectifiers.
A poorly designed Tube rectifier circuit is worse than a well designed Solid State rectifier circuit.
And, the reverse is also true:
A poorly designed Solid State rectifier circuit is worse than a well designed Tube rectifier circuit . . .
Attention to design details is needed (not just the rectifier circuit; but also all of the amplifier stages).
If reliability was only a function of good or bad luck, then I am going to Las Vegas (my tube amplifiers are reliable, Lucy me?).
YRMV (Your Reliability May Vary).
You can not enjoy listening to a dead amplifier.
Have Fun designing, building, and listening!
Years ago, I spent some time going back and forth between tube and solid state rectifiers in the same amps.
1. Tube rectifiers have higher impedance (internal resistance). This means current draw changes in the powered circuit will drop more volts (voltage 'sag'). Usually one can hear this in an audio power amp as a 'softer' bass response with perhaps more "bloom" (forgive the audiophile terminology). Taken to an extreme, this can sound muddy in the bass and lower midrange.
2. Solid state rectifiers have very low internal resistance, so changes in current drawn by the powered circuit will drop very little voltage (no 'sag'). I heard this as 'faster' and 'tighter' bass response from the amplifier. The opposite of "bloom".
I also had a big, ugly push-pull 300B amplifier running with its power supplies in a separate chassis. At one point I switched between a passive CLCRC type power supply and a tube regulated power supply (which was a beast with a 720VCT toroid, a giant 8H 400mA choke, and a 6336A pass tube). I found that the passive PSU made the amp sound 'softer' in the bass and lower mids, while the regulator had a 'tighter' more 'focused' sound. At the time I thought the regulator gave the amp a more 'electronic' sound, but I think the amp probably sounded better with that regulator powering it than the passive PSU. But this was a long, long time ago, so who knows.
The last three tube amp projects I've put together have been small ones. One is a headphone amp and the others were two RIAA phono preamps. I used solid state rectifiers in each, with no failed tubes due to turn on transients.
You can add a slow turn-on using a tube rectifier after solid state rectification. That way you can get the reliability of solid state rectifiers with the slow plate voltage ramp up of the tube rectifier. The tube rectifier now has a much easier job and should last a lot longer in this kind of use. Something like this:
Consider the largely varying load of a Class AB1 push pull amplifier: from quiescent state, to medium level power out, to full power out.
Generalization:
The B+ Voltage of a Capacitor input filter, varies widely versus wide load variations.
The B+ Voltage of a Choke input filter, varies slightly versus wide load variations.
All generalizations have exceptions.
Generalization:
The B+ Voltage of a Capacitor input filter, varies widely versus wide load variations.
The B+ Voltage of a Choke input filter, varies slightly versus wide load variations.
All generalizations have exceptions.
I can regulate both rise-up time and delay HV on time. I admit, design is quite complex to reach ripple on 80 dB level. Cost was round 60$ not countig transformer. Total perhaps 150$
That's right. Please note we are considering here single ended pure class A amplifier. This is totally different animal.
High vacuum (HV) rectifiers have favorable characteristics during turn-off and very low anode-cathode capacitance, which both contribute to reduced ringing effects from the power transformer's secondary windings. This ringing gets coupled into the B+ through the rectifiers and (usually) through the filament windings of the power transformer. HV rectifiers are kind of a pain, but they do make less spiky noise in an amplifier.
Of course, there are ways to mitigate the ringing, but still using semi-con rectifiers, by RC dampers and such. See especially Mark Johnson's work, ref: "Quasimodo".
All good fortune,
Chris
Of course, there are ways to mitigate the ringing, but still using semi-con rectifiers, by RC dampers and such. See especially Mark Johnson's work, ref: "Quasimodo".
All good fortune,
Chris
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