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In Reply to: RE: Full wave bridge into Choke PS posted by Triode_Kingdom on March 26, 2017 at 10:32:59
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?
Follow Ups:
"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"
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