Post by leonski on Nov 9, 2022 15:25:44 GMT -5
What is important is having sufficient energy storage for the specific design of the amplifier you're designing.
(Having insufficient capacitance or stored energy is going to handicap an amplifier...)
However the design determines to a large degree what amount is sufficient to begin with...
And most designs really don't benefit from more once you do have a sufficient amount...
However, even beyond specifics like that, there are some more general characteristics of specific types of designs.
For example the type of amplifier circuitry used in most modern solid state amplifiers has a relatively high immunity to power supply hum.
And, with a properly designed push-pull tube amplifier, a lot of the hum that is present on the B+ supply cancels out in the output transformer.
But, in a single-ended tube amp (like those SET designs), no such cancellation occurs, which makes them MUCH more sensitive to any hum that is present on the power supply.
I should also point out that, with power supply filter capacitors, the cost and size tend to be proportional to the amount of energy storage involved.
So that 10,000uF 450V capacitor is also going to be ten times the price, and ten times the size, of a 10,000uF 45V capacitor.
(And a typical vintage 50 watt tube amp is going to use more like 100uF or 120uF at 450V.)
And, for that matter, if you have an old tube amp...
Having sufficient energy storage is important...
But using a tube rectifier is going to limit the energy available to the output stage because it has a relatively high series impedance.
You could avoid that limitation to some degree by using lot of capacitance...
But too much extra capacitance is going to put a lot of extra strain on that rectifier tube as well being big and expensive...
And you can achieve the same benefit much more easily by using a solid state rectifier instead...
Fact is? When you get to a B+ of 400volts and higher? Energy storage goes WAY UP. This energy is measured in JOULES......and has nothing to do with Joules verne.....
I'd have to SEE that amp with 90k mfd of capacitance......at 40 volts,. that is going to be 72 joules. a LOT...... A tube amp? 10000mfd @450v is over 1000 joules......almost 15x.....
Let's take 2 amps with the same RMS power and way different amounts of energy storage. In the case of a SS amp? You might get 3db or even 6db of dynamic power.....Double or DoubleX2 the RMS rating. This is short time period, of cours.e
But? If you run 2 output devices per channel? You are running them (again depends) closer to 'redline' for the device. You won't get near the dynamic power.....without endangering the output devices......
A similar amp with a slightly different device, maybe 6 per channel, and more stored energy? You could start making weird claims like '35amps output current' (they dont' say short term) or other specified number.....While having the same RMS power rating. Of course? You are than into weight of amp / size and bulk with heatsink being a drive.....Not to mention sheer cost...
And YES, in this case Keith DOES have a case. You can 'over capacitance' an amp. Most tube stuff LOOKS feeble until you realize the PS caps run at B+ which is in the hundreds of volts......And is sometimes 'distributed'.
If you are worried about a Tube Rectifier? MANY designs can substitute (some other changes needed) a SOLID STATE part. Some feature thermisters for a 'slower' startup and very high current capacity AND very low 'sag' to the voltage
as demand rises. I'm guessing maybe 35$ each.......and a near-lifetime part.
Limits are reached in ripple reduction. Recharge becomes an issue (transformer limit?) and it is possible to induce a turn-on surge which is a danger to other parts in the circuit.
Running right at REDLINE, my old Carver Cube would 'dim' the lights in the house.....in time to the music. Amp had a 15amp fuse and was only 200x2 @8ohm. BUT? It ran COOL except when severely pressed. NO fan needed. And? It
was in the shape of about a 8" CUBE.
I'd like Keith to address 'Safe Operating Range'.....of an output device....which plays into all this
We can save tubes for later, but I'm slowly becoming a big fan. WITH the right speakers......
And in rereading my first post? I EXAGGERATED the size of tube amp capacitance. 10,000mfd? HUGE. The VTA 125 Mono amp? About 1000mfd total. And at about 500volts.....
That's 125 joules.....a goodly amount given Ratings of the amp.
