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

Bridge rectifier and voltage doubler from a single PT winding w/out CT?
Bridge rectifier and voltage doubler from a single PT winding w/out CT?
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 16th July 2019, 03:24 PM   #1
Sodacose is offline Sodacose  United States
diyAudio Member
 
Sodacose's Avatar
 
Join Date: Feb 2006
Location: mke, wi
Default Bridge rectifier and voltage doubler from a single PT winding w/out CT?

I'm having some trouble implementing the following schematic:

Click the image to open in full size.

I found the above in a schematic posted by Tubelab who was using it in a scrap box amplifier (powering heaters on B+ and screens with the 2x B+ I believe). I had a small PCB made for my purpose.

I get the expected voltages with a 12V PT and no load, but something is going wrong when installed with a 15VA 115V isolation transformer (I have verified unloaded AC voltage). The voltage droops and the PT starts heating up, this is without tubes installed.

In my build the ~150V B+ feeds a CLC filter and 40mA draw (transformer loaded tubes) and the ~300V 2x B+ feeds a MOSFET regulator with around 10mA load draw (low current phono circuit). I am testing without tubes and the regulator disconnected though.

The caps are all 250V rated. I've used bridge/Delon doublers in the past and with those, rating for 1/2 the doubled B+ (plus safety margin) is enough. But does that hold true with this doubler variation? In trying to wrap my head around the circuit, it still looks to me like the caps are charged to peak AC and standing on top of one another. Then again, a shorted cap might explain what I'm seeing (but no visible damage to the caps).

I've made plenty of dumb wiring mistakes before, but I'm not finding one here so I'm hoping someone else can double check the theory of this circuit.

Posting to the tube form because it seems to be a useful circuit for tubes IF I CAN GET THE DARNED THING TO WORK!

edit: link to the post where I found working version of the schematic Transformer secondary parallel out question

Last edited by Sodacose; 16th July 2019 at 08:23 PM.
  Reply With Quote
Old 16th July 2019, 04:11 PM   #2
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
diyAudio Member
 
JonSnell Electronic's Avatar
 
Join Date: Dec 2012
Location: The Jurassic Coast, England. GB
Why not use a voltage doubler.
Attached Images
File Type: png Screenshot 2019-07-16 at 17.10.21.png (30.2 KB, 145 views)
__________________
Support for Fender, Marshall and all Valve Equipment; Audio Innovations, Audiorama FU29, Quad and Leak. www.jonsnell.co.uk
  Reply With Quote
Old 16th July 2019, 04:50 PM   #3
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
I think the OP schematic is an attempt at a full wave doubler. There's something about it that seems strange, especially in combination with the bridge rectifier.
  Reply With Quote
Old 16th July 2019, 04:52 PM   #4
leadbelly is online now leadbelly  Canada
diyAudio Member
 
leadbelly's Avatar
 
Join Date: Dec 2002
Location: Calgary, Alberta
AFAIK all multiple tapped doublers of all types collapse when current draws from the taps are not matched.
__________________
Wise men speak because they have something to say; Fools because they have to say something. Plato
  Reply With Quote
Old 16th July 2019, 07:42 PM   #5
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
diyAudio Member
 
JonSnell Electronic's Avatar
 
Join Date: Dec 2012
Location: The Jurassic Coast, England. GB
It cannot work with full wave bridges. Think about what is happening. It is basically one supply rail and if one puts them in series, there is a diode at across the winding.
Keep it simple and it will work.
__________________
Support for Fender, Marshall and all Valve Equipment; Audio Innovations, Audiorama FU29, Quad and Leak. www.jonsnell.co.uk
  Reply With Quote
Old 16th July 2019, 08:13 PM   #6
Sodacose is offline Sodacose  United States
diyAudio Member
 
Sodacose's Avatar
 
Join Date: Feb 2006
Location: mke, wi
Quote:
Originally Posted by leadbelly View Post
AFAIK all multiple tapped doublers of all types collapse when current draws from the taps are not matched.
This is what I believe I've read elsewhere but I don't have experience to back it up.

An alternative solution to what I'm trying to do is here:

Tube Power Supply PCB

This uses a single winding but requires a center tap. Part of my goal was to use cheap and widely available isolation transformers to get multiple voltages. A transformer with a 230V CT secondary may work, but I'm still curious about the schematic in the OP.

It works at least according to Tubelab. I'll try to dig up the discussion where I found it.

edit: here's the post and schematic in quest: Transformer secondary parallel out question claims to be working amplifier

Last edited by Sodacose; 16th July 2019 at 08:20 PM.
  Reply With Quote
Old 18th July 2019, 10:04 AM   #7
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
The circuit in post 1 looks fine to me. None of the newbie errors we usually see when someone tries to run two PSUs off one secondary.

I am going to guess that you have one of the caps reversed. This would be just about OK on low voltage but would show up on high voltage.

15VA is a bit too small for this, as you are expecting to draw 9W DC.
  Reply With Quote
Old 18th July 2019, 10:17 AM   #8
tikiroo is offline tikiroo  New Zealand
diyAudio Member
 
Join Date: Nov 2007
Location: New Plymouth
It's described quite well in the best voltage doubler -the 4X8!
  Reply With Quote
Old 18th July 2019, 10:47 AM   #9
Tubelab_com is offline Tubelab_com  United States
diyAudio Member
 
Tubelab_com's Avatar
 
Join Date: Jul 2005
Location: West Virginia panhandle
Quote:
I think the OP schematic is an attempt at a full wave doubler.......It cannot work with full wave bridges.
I have built several of these and they DO work. The amp shown in the schematic that is linked in post #6 is still alive and well as built about 8 years ago.

I see two possible issues.

Quote:
The caps are all 250V rated.
This circuit will produce 330 to 350 volts in normal operation depending on line voltage and the fact that isolation transformers are not actually 1:1. It may produce quite a bit more unloaded if your live voltage is distorted or noisy. C4 should be a 400 volt cap. All the others can be 250 volts.

The current in any rectified power supply is drawn in short pulses at the peak of the AC cycle. Use of tube rectifiers blunt this peak somewhat, but this circuit uses silicon. On any given peak there are two diodes feeding hungry caps in parallel in this design since it is essentially two power supplies on one transformer. A small power transformer may be operating near saturation when operated into a resistive load, and may overheat when feeding rectifiers. This should not happen with no load at all though.

I have found that an isolation transformer needs to be derated a bit when feeding diode rectifiers. I tend to suck no more than 35 watts from a 50 VA Triad N-68X when using diode rectification. The amp design shown in the link on post #6 used a 100VA isolation transformer to feed a guitar amp that draws about 40 watts at idle and 70 watts at full power (17 watts output).
__________________
Tubelab, it's 5 year mission. To explore strange new tubes, to seek out new circuits and topologies, to boldly go where no tube has gone before......
  Reply With Quote
Old 18th July 2019, 12:06 PM   #10
Ketje is offline Ketje  Belgium
diyAudio Member
 
Ketje's Avatar
 
Join Date: Dec 2012
Location: Flanders
Drawing it a little different makes it more easy to understand.
To prevent charging the capacitor in the wrong direction, the original put bigger ones in the first stage of the doubler.
With two diodes you can use the same value for all.
Mona
Attached Images
File Type: png Single-Double.png (32.6 KB, 96 views)
  Reply With Quote

Reply


Bridge rectifier and voltage doubler from a single PT winding w/out CT?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
Voltage Doubler & Normal Full Wave Rectifier on Same Winding ballpencil Power Supplies 6 5th July 2014 12:23 PM
Damper rectifier tubes & voltage doubler jono1 Power Supplies 10 11th February 2012 05:05 PM
Bridge rectifier voltage question woody Power Supplies 1 1st May 2008 12:47 AM
Bridge Rectifier Replacements and Single-to-Quad Adapters?? Sampsa Parts 0 15th June 2004 03:09 AM
Voltage Doubler Rectifier suitable for GC? EnvisionAudio Chip Amps 0 3rd March 2004 03:22 AM


New To Site? Need Help?

All times are GMT. The time now is 06:12 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki