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Don't see many schematics with this arrangement. Any drawbacks or disadvantages? Seems like a good way of getting HV out of a low voltage transformer. TIA
Follow Ups:
How does the value of a "small" cap which is used to adjust the voltage affect the choke input "smoothing" or hash reduction capability?
There's small and there's very small. A 0.01 muF. part is used for kickback spike protection. A part less than 1 muF. is used as a "fudge factor" to adjust the rail voltage. At some point, critical current behavior will cease and cap. I/P filtration behavior will begin. What the exact value is has to be determined on a case by case basis. I'm very suspicious of both a cap. value greater than 0.47 muF. and an attempt to significantly raise the rail voltage above the RMS value being rectified. A volt or 2 above RMS might be OK.
The bottom line is that "breadboarding" and measuring, on the bench, can't be eschewed in favor of simulations.
Eli D.
Morgan Jones in the 4th ed. of his book has a pretty comprehensive discussion of this subject.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
We did empirical work years ago.VOLTAGE never moved in a choke input supply until the capacitance moved past .68 uF ...Is not lost on me .68 is a benchmark value. Interestingly, the voltage never increased more after 8 uF. Perhaps with a high or lower test VOLTAGE, these numbers might change.
The Mind has No Firewall~ U.S. Army War College.
Edits: 03/29/17
Were you measuring the setups under load? I suspect you would have noticed a droop, when that 8 μF. had to supply substantial current. Small valued cap. I/P filters are notorious for poor regulation.
Eli D.
At idle Eli, there was no signal present.
The Mind has No Firewall~ U.S. Army War College.
If you use SS diodes anywhere in the bridge, be sure to use either a snubber cap. or MOV, as protection against inductive kick back spikes. Think cLC filter, where c is 0.01 μF. and its WVDC is very large.
Eli D.
I parallel every diode with a 0.01u disc cap and 470K resistor (values not critical). This has been a standard commercial treatment for more than 50 years.
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Buy Chinese. Bury freedom.
"I parallel every diode with a 0.01u disc cap and 470K resistor (values not critical)."A very reasonable action, when most PN junction diodes are employed. FREDs can exhibit "funny" behavior, when snubbed. Snubbing diodes is unnecessary, when they are Schottkys.
The single snubber I mentioned is specifically for choke I/P filters associated with SS diodes. Without the cap. or MOV, inductive kick back spikes can destroy SS diodes. The situation is 1 where the electrical fragility of SS is illustrated.
Tubes are mechanically fragile and electrically robust. SS parts are mechanically robust and electrically fragile.
Eli D.
Edits: 03/28/17
OK what's a MOV? and if I follow the LC section with another LC section is it really needed?
MOV = metal oxide varistor. They are what make surge suppressor power strips work.
Regardless of what you follow an I/P LC section with, inductive kick back spikes are a potential source of SS diode destruction. "An ounce of prevention is worth a pound of cure."
A link to a modestly price part that will get the job done is provided below.
Eli D.
I presume that each diode in the bridge is paralleled with one of these snubbing caps? Thanks for the link, much appreciated.
Only 1 snubber, connected between the bridge's O/P and ground, is needed. Remember, think cLC filter, where the 1st cap. is tiny .
Eli D.
Thanks, very cool and very easy to implement.
No drawbacks. Just remember to halve the current rating of the transformer.
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Buy Chinese. Bury freedom.
Hmm, thought the formula was 0.9 x secondary current for the output. Same for voltage if i am not mistaken. Have you used such an arrangement before?
"thought the formula was 0.9 x secondary current for the output. "
When the circuit is changed from full wave CT rectification to a full wave bridge, voltage is doubled and current draw must be halved. It's a simple IxE (power) calculation. Whether the original full wave rating was intended to apply to choke or capacitor input is a different issue.
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Buy Chinese. Bury freedom.
My understanding is based on this...
The PDF you linked is manufacturer-specific. In this case, Hammond is indicating the difference in the relative volt-amp rating of the transformer when comparing a full wave CT to a full wave bridge. The image below shows the two configurations side by side. I've picked the resistive load examples so as not to confuse this issue with choke vs capacitive input filters.
Note that the transformer can be operated at a higher volt-amp rating when using the full wave bridge. This has to do with factors such as core size/construction and wire gauge. The specific numbers shown above are not universal, however. In the absence of such data, the manufacturer's rating for the full wave CT configuration (usually how the ratings are derived and often printed on the transformer) should be used for both configurations. This means that doubling the voltage output by changing from the CT to the bridge requires limiting the transformer secondary to half the current. That maintains the same volt-amp rating.
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Buy Chinese. Bury freedom.
Edits: 03/27/17
I am using a Hammond product so feel reasonably confident about following their recommendations. Which in the case I am enquiring about DC volts equals 0.9 times AC volts, and DC current equals 0.94 times AC current. I guess I am too dim to understand the point you are trying to make, I think very few people in our hobby actually use the rectified output into a resistive load. All I really wanted to know was if there are any drawbacks to such a configuration. My thanks for your patience in explaining.
These hum like hell if run within 75% of rating based on my experience.
I would also verify with PSUD program
That's your experience, certainly not been mine.
Choke input topology can be used with either a full wave CT or full wave bridge configuration. As Triode Kingdom has stated: one will yield half the voltage but twice the current (full wave CT) than the other. Once that issue has been decided, then one has to consider choke input or capacitive input (or in between, but let's leave that for a future discussion). As has been pointed out choke input yields about 0.9 times the RMS output voltage of the transformer, capacitive input about 1.4 times. The big disadvantage of choke input is less voltage. The advantage? Choke input supplies draw power though the PS transformer almost continuously; capacitive input supplies in sharp, short pulses. This generates harmonics of the line frequency that can reach to the RF region. Avoiding this "hash" rather than trying to mitigate its effects is, in my opinion, one of the main reasons to use choke input and worth the price of less voltage.
Disclaimer: I use choke input for virtually everything.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
Thanks for your response. Choke input also means better voltage regulation if I am not mistaken.
Choke input provides better average regulation. Peak regulation - which likely has just as much impact on the music - is much worse. For this reason, choke input supplies require more storage capacitance than would otherwise be required to merely eliminate ripple. The combination of L and C can also create resonances and other undesired behavior. It's a good idea to always use SPICE to simulate the output impedance of any supply powering an audio amplifier, particularly when it uses both chokes and filter capacitors.
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Buy Chinese. Bury freedom.
10 Henry/45 uF / 8 Henry / 45 uF... SE 45 5842 input tube... LED bias
Dead quiet through modified Khorns. Some audio guys would be quite surprised by the bass slam. I never use electrolytics in my builds.
DCR of both chokes.. the 10 @ 35 ohms, the 8 is 25 ohms
That iron is HARD to find
The Mind has No Firewall~ U.S. Army War College.
What do you use for rectification?
(that info would just make TK's sim better, if he doesn't mind running it again)
Thanks
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
275 volts before 1500 ohm resistor (45)/two 816 Mercury vapor rectifiers
Power transformer is not the 5 ohm one I wanted to use (not enough real estate) Is a.NOS 180 ma one ... Chicago I believe. All the filament transformers are separate, except for the 6 volt windings for the 5842.
Probably been running non stop for 4 months.
The Mind has No Firewall~ U.S. Army War College.
That filter sims really well. Output Z very low, doesn't do anything untoward until roughly 15 Hz. Nice!
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Buy Chinese. Bury freedom.
Hard to find and weighs a TON!
!
The Mind has No Firewall~ U.S. Army War College.
Hammond rates their power transformers for FULL WAVE Capacitor Input
For a full wave bridge, choke input it's 94% of that rating.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
You halve the current rating into a FWB Cap loaded and you get 1.41 times more voltage. In a FWB Choke loaded it is 0.9 DC voltage and 0.94 DC current.
He probably is cap loading if he wants the voltage boost.
How is it that at lower voltage output, the current capability goes lower than the 'DC current'. BTW, what is the 'DC current' referring to, and how is this rating achieved?
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
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