|
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: Tube voltage doubler posted by Tre' on May 02, 2016 at 14:04:18
Here is a sim of the Typical Operation from the datasheet, 450vrms per plate and 85 ohms effective plate supply impedance per plate with the input cap at 40uf and a load current of 225ma.
The peak repetitive current maximum of 800ma., called "current forward repetitive maximum" by the simulator program and "Steady State Peak Plate Current Maximum" on the datasheet, is being exceeded by 11.51ma. repeatedly.
On the other hand if I decrease the DCR of the secondary winding to 50 ohms (25 ohms per half winding...per plate) the peak current goes to 916.89ma.
If the load current is decreased from 225ma. to 100ma. then the peak repetitive current drops to 507ma. with the DCR of the winding at 25 ohms per plate. and 456ma. when the DCR is 85 ohms per plate.
The point is, the DCR of the power transformer winding, the value of the input cap and the load current are all part of the equation when trying to discern if the peak repetitive current rating of the rectifier tube is going to be exceeded.
The capacitor value given in the datasheet is only the max value for the operating condition given. It's not a one size fits all value.
It's not the capacitor value given in the datasheet that shouldn't be exceeded, it's the peak repetitive current maximum rating of the tube that can not be exceeded without causing harm to the tube.
The maximum cap value will be different for each different set of operating conditions.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Follow Ups:
" 85 ohms effective plate supply impedance per plate with the input cap at 40uf and a load current of 225ma". 800ma peak repetitive, ouch! Ive juggled input cap values and their ESR in psud and noted the peak repetitive power transformer current. What really hit it home is 1sr hand experience feeling the transformer operating temp. Of a cap input vs choke input supply. It is not subtle. Needless to say I've been sticking to tiny c input supplies, just enough capacitance they snub and save sand rectifiers. JH
It's not front page NY Times news that the full VA capability of power transformers is unavailable, when cap. I/P filtration is employed.
I 2 R heating associated with cap. charging pulses must accounted for. I frequently call for LARGE caps. in the stacks of SS diode doubler B+ PSUs. If the winding being rectified is rated for n mA. RMS, only n/4 mA. is available as DC. TANSTAAFL!
Choke I/P filters are current rich and voltage poor. Cap. I/P filters are voltage rich and current poor. Did you ever get the impression that someone "has it in for us"? ;> )
BTW, if power magnetics are warm to the touch, but are not too hot to remain in contact with, things are OK. If the hand has to be withdrawn, correction(s) are required.
Eli D.
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: