|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
76.90.39.24
In Reply to: RE: GZ34: getting too much voltage drop posted by sideliner on February 11, 2017 at 12:20:38
0.9*Vrms(trans. sec.) for choke input works out to .45*Vrms when the transformer secondary has a grounded CT.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Follow Ups:
This is correct and it's not my point of contention. It's of course either 0.9x taking it from one end of the transformer to the CT or 0.45x taking it from end-to-end. My point is that at the input of the filter - be it choke input or cap input, the VAC RMS is equal to the RMS at the secondary minus whatever drop occurs at the rectifier.In this case the math simply doesn't work out to justify the 290V at the rectifier's cathode as shown on the attached schematic. That's why I suggested that the OP confirms that the no-load voltage at the secondaries is as it should be.
Edits: 02/11/17
"My point is that at the input of the filter - be it choke input or cap input, the VAC RMS is equal to the RMS at the secondary minus whatever drop occurs at the rectifier."No. A cap input filter will cause the voltage and charging currents to be higher at the cathode of the rectifier tube.
A critical inductance choke input will cause the voltage and charging currents to be lower at the cathode of the rectifier tube.
Cap vs. choke input filter changes the way the rectifier tube works.
The equation "VDC=0.9*Vrms(trans. sec.) for choke input" or "VCD=1.41*Vrms for cap input" is the input to the filter.
I just ran a sim 335-0-335 into a 5ar4 with a critical inductance input choke and depending on the DCR of the power transformer secondary and the total current draw, 290vdc at the cathode of the 5ar4 is about right.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 02/11/17 02/11/17 02/11/17
You are right, I thought more about this after I posted my last response and it occurred to me that the losses incurred in the filter from input to output can only be the resistive losses in the inductor (DCR) and/or resistors. From this realization alone it's obvious that the difference between 1.41x Vrms and 0.9x Vrms in the two types of filters is due to the topology.
The capacitor input simply charges to the peak value of the voltage waveform, hence the x1.41 factor. So to correct my earlier statement, the voltage at the output of the filter is that of the input minus the resistive losses of the chokes and resistors which of course depends on the current draw of the amp.
So, the voltage of 290V present at the rectifier's cathode is actually in line with the expected result.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
That looks like the diagram in the Hammond Transformers catalog.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: