Hello all
I've been given a power transformer and I know what the windings are rated at but I'm confused about the numbers on the secondary and how I should wire it up.
I have a project in the back of my mind which needs about 400VDC on the B+ so I'm wondering if this transformer will be any use to me for this.
The secondary is shown as 275-190-0 but there is a note which describes the options and that's what confuses me. It says;
0-275 winding for approx 360VDC
0-190 winding for approx 260VDC
190-275 winding for approx 115VDC
I thought 0-275 would be supplying 275VAC to the rectifier so depending on the tube I'd get a little bit less VDC out. The same principle would apply to 0-190 and 190-275 would be 85VAC to the rectifier.
Can someone please explain how this works.....
I've been given a power transformer and I know what the windings are rated at but I'm confused about the numbers on the secondary and how I should wire it up.
I have a project in the back of my mind which needs about 400VDC on the B+ so I'm wondering if this transformer will be any use to me for this.
The secondary is shown as 275-190-0 but there is a note which describes the options and that's what confuses me. It says;
0-275 winding for approx 360VDC
0-190 winding for approx 260VDC
190-275 winding for approx 115VDC
I thought 0-275 would be supplying 275VAC to the rectifier so depending on the tube I'd get a little bit less VDC out. The same principle would apply to 0-190 and 190-275 would be 85VAC to the rectifier.
Can someone please explain how this works.....
I reckon those DC numbers are for post-rectification by diodes, not tube rectifiers. Working with a raw DC value of 1.414x the AC voltage gives the following:
275VAC > 389VDC
190VAC > 267VDC
85VAC > 120VDC
Take into account the diode losses etc. you get very close to those stated approx. values
275VAC > 389VDC
190VAC > 267VDC
85VAC > 120VDC
Take into account the diode losses etc. you get very close to those stated approx. values
of course.... I must have my stupid head on today 
I forgot about the 1.414x thing.... I was thinking about the voltage drop in the tube (about 30V) and just taking that off 275 to get the VDC value.
Thank you.....
I forgot about the 1.414x thing.... I was thinking about the voltage drop in the tube (about 30V) and just taking that off 275 to get the VDC value.
Thank you.....
I know what you mean. I seem to vacillate between the stupid head and the vaguely-competent head most days. The kinda-smart head has been gathering dust on the hatstand for ages 😀
Depending on the tfmr secondary winding current rating and tfmr regulation multiplying by 1.35 might give you a more accurate DC figure, HV wndg's drop more too when loaded so 350v DC for the 0 - 275v might be a more accurate result.
To figure out if a tfmr is any good draw a load line or figure out what your OP stage needs, 1.5 times the quiescent current should be about right, then add on 10mA or so for the PS and other valves. For a stereo amp double it.
Using ohms law find a big resistor of about the right value, load the tfmr sec wndg, if the voltage drops by less than 10% you should be fine.
Andy.
To figure out if a tfmr is any good draw a load line or figure out what your OP stage needs, 1.5 times the quiescent current should be about right, then add on 10mA or so for the PS and other valves. For a stereo amp double it.
Using ohms law find a big resistor of about the right value, load the tfmr sec wndg, if the voltage drops by less than 10% you should be fine.
Andy.