Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Age-old question: reverse, perverse engineering of surplus power xfmrs.
Age-old question: reverse, perverse engineering of surplus power xfmrs.
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 9th September 2019, 03:13 PM   #11
Elvee is offline Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
Quote:
Originally Posted by multi-volti View Post

The V^2/R sum of the three secondaries (one for B+ with voltage doubler, and two for unrectified filament heater use) was about 12420...approximately 67% of the primary's.
It could be caused by a sloppy design (or the need to use certain wire gauges), or by very poor quality iron requiring a disproportionate magnetising current

Quote:
Interestingly, the smaller transformer with a tapped (high and normal 115 V) primary and three secondaries (only one was a very small filament winding) had a secondary V^2/R 'factor' of about 12400 also, but the primary calculation was less, about 7700. That's the disturbing thing...12400/7700 is 1.6, not less that 1.0.
The tap is too small to have a significant influence on the global result: things would be different for older multivoltage primaries: 110, 120, 140, 190, 220, 240V.
An explanation could be that not all secondaries are meant to be used simultaneously
__________________
. .Circlophone your life !!!! . . ♫♪ My little cheap Circlophoneİ ♫♪
Electrify your daily life!!! ....⚡⚡ ELEKTRIA ⚡⚡
  Reply With Quote
Old 10th September 2019, 04:17 AM   #12
multi-volti is offline multi-volti  United States
diyAudio Member
 
multi-volti's Avatar
 
Join Date: May 2005
Location: Michigan
Thank you.

The smaller one does produce multiple voltages from one winding (bridge and reversed HWR) in addition to powering a degaussing coil in parallel with a thermistor in series with the winding before it reaches the bridge.

I spent some time today comparing some filament winding ac VA to the windings that have a bridge or doubler to 'select' a derating factor. I use a VA reduction factor of 1.8 for bridge rectifier, and decided I should double that for doubler. I have not seen that in writing anywhere but it seems to 'adjust' the V^2/R to VA ratio to be in the range of the other windings' ratios.

Then I compare the c.m. value for each winding. I'll be choosing 'my' current rating and then find some load resistors next and see how warm it gets.
__________________
Murray
  Reply With Quote
Old 10th September 2019, 02:59 PM   #13
multi-volti is offline multi-volti  United States
diyAudio Member
 
multi-volti's Avatar
 
Join Date: May 2005
Location: Michigan
These also have
some of the the 'old-school' characteristics you mentioned...

In some cases a tapped primary, overlaid windings rather than split bobbin, and a maximum temperature rise with some 'test circuit'. The max. core losses & magnetizing current are also specified for the one I found data for.

Thanks for your help.
Hopefully, I'll choose my factors safely & conservatively.
__________________
Murray
  Reply With Quote
Old 10th September 2019, 04:22 PM   #14
Elvee is offline Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
Quote:
Originally Posted by multi-volti View Post
The smaller one does produce multiple voltages from one winding (bridge and reversed HWR) in addition to powering a degaussing coil in parallel with a thermistor in series with the winding before it reaches the bridge.
For the degaussing winding, it does not "exist" in the original planning of the transformer, because of the thermal time-constant.
Of course, if you decide to use it on a permanent basis, it has to be part of your new global calculation.

Quote:
I use a VA reduction factor of 1.8 for bridge rectifier, and decided I should double that for doubler. I have not seen that in writing anywhere but it seems to 'adjust' the V^2/R to VA ratio to be in the range of the other windings' ratios.
Contrary to a common belief, the PF of a doubler is not very different from a fullwave rectifier.
What I mean is that a winding capable of providing 12V/1A DC after rect+filt will deliver practically 24V/0.5 DC with any type of doubler.
I have made a thread on the subject several years ago


Quote:
Originally Posted by multi-volti View Post
These also have
some of the the 'old-school' characteristics you mentioned...

In some cases a tapped primary, overlaid windings rather than split bobbin, and a maximum temperature rise with some 'test circuit'. The max. core losses & magnetizing current are also specified for the one I found data for.

Thanks for your help.
Hopefully, I'll choose my factors safely & conservatively.
With overlaid windings, the primary is generally the innermost winding, meaning it will mechanically have a higher power coefficient because of the shorter turn length, yet it will be the most susceptible to heating, so all of that has been said has to be taken with an open mind, a pinch of salt and a good portion of context.
__________________
. .Circlophone your life !!!! . . ♫♪ My little cheap Circlophoneİ ♫♪
Electrify your daily life!!! ....⚡⚡ ELEKTRIA ⚡⚡
  Reply With Quote
Old 17th November 2019, 05:26 PM   #15
multi-volti is offline multi-volti  United States
diyAudio Member
 
multi-volti's Avatar
 
Join Date: May 2005
Location: Michigan
I found 24-year-old notes dating to when I actually had data for this no-longer-mystery transformer. Now I can compare specs to estimates.

primary 60 Hz 0-120(normal line)-128(high line)

sec. #1 derives two DC voltages
1) 59vct FWB across full winding(CT floating)+600 uF 77VDC@0.18ADC 0.020" AWG25 320 c.m.
2) ct to 500 uF produces 37.5 VDC @ 0.28A (appears to be HWR by one leg of the FWB)

sec#2 was drawn in notebook as two windings internally, and I did find two wire gauges. Schematic shows 0-125-200vac.
0-125 is 0.032", AWG21, 812 c.m. applied to FWB+300 uF: 158VDC@0.77ADC
'upper' 75 (125-200) is 0.015", AWG27, 202 c.m., HWR+100 uF adds ~100VDC in series with 158VDC: 268VDC/0.025ADC

sec#3 is strange. 1.3vac/0.9a ac, was in series with 5vac/0.9aac winding on 2nd transformer (I don't have) for CRT preheating/instant-on feature. Useless on this xfmr by itself, and wire is only 0.011", AWG30 100 c.m. (my diameter measurement was reference for c.m. and AWG 'labels'). Seems undersized by any c.m./A rule of thumb.

Looking at DC current ratings and contemplating c.m./A, I'm reminded that it is probably properly applicable to transformer AC VA rating and is skewed by rectification and filter capacitor size...the only winding I would want to 'squeeze' more out of is the 75 vac AWG27 winding in series with the 125 vac AWG21 one. If I used the 0-125-200 'series' winding with ONE FWB across the full dual winding, maybe 268 VDC upped to 200 mA. Or use the 158 VDC/0.77ADC winding with a doubler at half the current (or derate that a little if uptight), or move the ground point to have 75-0-125 vac, with a doubler on the 125 and FWB on the low-current 75vac winding & use for filament supply elevation for totem-pole circuit upper tubes, or negative HWR for a bias supply.

Murray
__________________
Murray
  Reply With Quote
Old 17th November 2019, 06:02 PM   #16
multi-volti is offline multi-volti  United States
diyAudio Member
 
multi-volti's Avatar
 
Join Date: May 2005
Location: Michigan
Or just put all windings in series:
125+75+59=259vac. The 0.18ADC rating of the 59 v winding is close enough to my target of 0.2ADC for the 125+75, limited by the 75v AWG27 winding.

Been saving a couple cartons of these since 1995, and they get heavier every year!

I have separate 6.3 V filament transformers.
__________________
Murray
  Reply With Quote
Old 27th November 2019, 04:30 AM   #17
Rick PA Stadel is offline Rick PA Stadel  United States
diyAudio Member
 
Join Date: Apr 2017
Location: greater Kansas City
Hi Murray,

I just have one little tip to add -- and it sounds like you came around to it already --

On 'compound' windings (where wire size changes at a tap) I always assign my '0' toward the heavier-gauge end.

Also, sure feel ya' on the 'heavier every year'. Thinking of how much harder it got between our last two moves, the next one gives me a real chill. And wives notice those cartons, too -- and how heavy they are!

Regards, Rick

Last edited by Rick PA Stadel; 27th November 2019 at 04:44 AM.
  Reply With Quote

Reply


Age-old question: reverse, perverse engineering of surplus power xfmrs.Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Reverse engineering Krell KMA 160 jwb Solid State 220 14th August 2019 12:01 AM
Attempted reverse engineering. ALPUY Analogue Source 14 22nd March 2017 03:38 AM
Reverse engineering to drivers kevinsullivan Multi-Way 21 6th October 2012 04:20 AM
reverse engineering a box Zero Cool Multi-Way 1 16th July 2007 11:00 PM


New To Site? Need Help?

All times are GMT. The time now is 04:58 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki