confused on power transformer ratings - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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 23rd August 2010, 01:22 AM   #11
diyAudio Member
 
Join Date: Feb 2009
1uf, 5 henry, then the main 100uf cap. I can use this scheme to adjust my b+ alot between 300 and 425 which is what im shooting for. Right now im using the antek AN-4T360 360vac @550ma in the simulations.

It seems to fit the bill as i need 350-450 swing for the el34's and kt120's. The kt120s seem to want 250ma per pair at the low 400v mark for max output, but the el34s only need 125ma per pair at 300-350v.


Thanks alot for the simulation help. It cleared things up alot.

PS: how do you sum 2 chokes in parallel since its hard to find a 3-5 henry choke in the high current range? If its 2 5 henry 150ohm units at 200ma, does that turn them into 2.5 henry 75ohm 400ma single unit for the simulator?

Last edited by nightanole; 23rd August 2010 at 01:25 AM.
  Reply With Quote
Old 23rd August 2010, 03:39 AM   #12
TheGimp is offline TheGimp  United States
diyAudio Member
 
TheGimp's Avatar
 
Join Date: Aug 2009
Location: Johnson City, TN
Yes, paralleling chokes of equal value will result in an equivalent choke with 1/2 the inductance. They may not share current equally if the values aren't close to each other and the dc resistances match closely.

One thing I've finally realized is that the ratings should be viewed as as VA. Look at your voltage at the first filter cap and use it to calculate the available current by dividing it into the VA rating. Then derate it.
  Reply With Quote
Old 23rd August 2010, 04:01 PM   #13
diyAudio Member
 
boywonder's Avatar
 
Join Date: Jan 2008
Location: So.Cal.
Quote:
Originally Posted by nightanole View Post

PS: how do you sum 2 chokes in parallel since its hard to find a 3-5 henry choke in the high current range? If its 2 5 henry 150ohm units at 200ma, does that turn them into 2.5 henry 75ohm 400ma single unit for the simulator?
Check out the Hammond 193 series of chokes, they have up to 10H @ 300ma. These are the enclosed, mount on top style.

Also keep in mind that the choke current rating needs to be at least equal to the sum of the desired B+ current + the ripple current.

For 60hz mains, the ripple current=Vin(rms)/(1386L), where L is the choke inductance in Henries.

Last edited by boywonder; 23rd August 2010 at 04:05 PM.
  Reply With Quote
Old 23rd August 2010, 04:10 PM   #14
TheGimp is offline TheGimp  United States
diyAudio Member
 
TheGimp's Avatar
 
Join Date: Aug 2009
Location: Johnson City, TN
Shouldn't the ripple current =(Vin(rms)-Voltage on cap) /1386L ?

Since the voltage across the inductor is the AC source minus the B+ at the first cap.
  Reply With Quote
Old 24th August 2010, 03:22 AM   #15
diyAudio Member
 
boywonder's Avatar
 
Join Date: Jan 2008
Location: So.Cal.
Quote:
Originally Posted by TheGimp View Post
Shouldn't the ripple current =(Vin(rms)-Voltage on cap) /1386L ?

Since the voltage across the inductor is the AC source minus the B+ at the first cap.

Gimp: The formula above is straight out of Morgan Jones' Valve Amplifiers, 3rd ed. Page 314.
  Reply With Quote
Old 24th August 2010, 03:34 AM   #16
TheGimp is offline TheGimp  United States
diyAudio Member
 
TheGimp's Avatar
 
Join Date: Aug 2009
Location: Johnson City, TN
Just seems logical to me that the DC voltage on the filter side of the choke should not contribute to ripple current.Only the ripple voltage (ie ac component) should be involved.

I'll go read the chapter as I am probably misinterpreting the formula.
  Reply With Quote
Old 26th August 2010, 03:49 PM   #17
diyAudio Member
 
Join Date: Feb 2009
So should i go with a 400vac choke/pi loaded transformer, or a 300vac crc loaded transformer? From what i gather, a choke loaded unit will heat up the power transformer half as much as a cap loaded input.
  Reply With Quote
Old 26th August 2010, 05:46 PM   #18
diyAudio Member
 
boywonder's Avatar
 
Join Date: Jan 2008
Location: So.Cal.
Among other things, think about cap voltage ratings at startup. A 400V secondary will exceed 550v B+ on start up with cold tubes; the 300v secondary will be about 420v or so. For the 400V transformer, you can always series stack the caps (with equal balancing resistors) for additional voltage rating at the expense of halving the uf, or series paralleling for twice the voltage rating, same uf, and 4 times the number of caps.

With a cap input filter, I would consider a CLC instead of a CRC.

If you need the 300V-425V B+ adjustability, a good compromise (as you've already modeled), is a transformer around 350V or so and varying the value of C1. This will also allow 500V caps to be used, which are reasonably available.
  Reply With Quote
Old 26th August 2010, 06:17 PM   #19
Brit01 is offline Brit01  United Kingdom
diyAudio Member
 
Join Date: Jul 2008
I have a similar question.

First time buy with a CT 350-0-350.

Using PSUII I need to select Full Wave and insert 350V as the voltage to get around 350 Volts(of course depending on the filtering I choose)?

If I need 700V I would connect the 2 outer cables to a bridge (Centre tap goes to ground?)
  Reply With Quote
Old 26th August 2010, 08:12 PM   #20
diyAudio Member
 
Join Date: Feb 2009
Quote:
Originally Posted by Brit01 View Post
I have a similar question.

First time buy with a CT 350-0-350.

Using PSUII I need to select Full Wave and insert 350V as the voltage to get around 350 Volts(of course depending on the filtering I choose)?

If I need 700V I would connect the 2 outer cables to a bridge (Centre tap goes to ground?)
I dont think you connect the center tap to anything, or you would get this:

http://i38.tinypic.com/14nzdro.gif
  Reply With Quote

Reply


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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Transformer Ratings jt1 Tubes / Valves 7 31st March 2010 10:36 AM
Output transformer current and power ratings boywonder Tubes / Valves 3 29th April 2009 10:00 PM
Question about Allied & Hammond Power Transformer Ratings Bitrex Tubes / Valves 2 6th March 2009 08:31 AM
Transformer ratings??? AR1 Power Supplies 2 2nd May 2005 08:02 PM
Power supply transformer ratings deskmate88 Chip Amps 4 29th January 2004 06:29 AM


New To Site? Need Help?

All times are GMT. The time now is 05:38 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2