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 11th February 2013, 03:37 PM   #1
diyAudio Member
 
Join Date: Feb 2013
Default Silly transformer question

Looking at output transformers, I see ones listed as push-pull, 8000 ohms center tapped. Is that 8000 in each leg, or 8000 from plate to plate?
  Reply With Quote
Old 11th February 2013, 03:52 PM   #2
rmyauck is offline rmyauck  Canada
diyAudio Member
 
Join Date: Apr 2009
Quote:
Originally Posted by sparkydave View Post
Looking at output transformers, I see ones listed as push-pull, 8000 ohms center tapped. Is that 8000 in each leg, or 8000 from plate to plate?
Not silly! Plate to plate is the usual way they are spec'd.

Randy
  Reply With Quote
Old 11th February 2013, 03:58 PM   #3
diyAudio Member
 
JohnAtwood's Avatar
 
Join Date: May 2006
Location: Rural Nevada
This usually means 8000 ohms plate-to-plate (often written as 8000 P-P). Don't forget that the impedance is proportional to the square of the turns ratio, so if the transformer primary was 8000 ohms each leg, then it would be 32000 ohms plate-to-plate (double the primary windings, thus 2^2 or 4 times the impedance.)

- John
  Reply With Quote
Old 11th February 2013, 05:13 PM   #4
diyAudio Member
 
Join Date: Feb 2013
Thanks! I was pretty sure it meant plate-to-plate. Interestingly, I stumped one of the electrical engineers where I worked when I wondered if one leg of this 8000 ohm transformer would look like 2000 ohms or 4000 ohms, but when I did the math it would be 2000 ohms as John pointed out. Glad I remember something about transformers from school.
  Reply With Quote
Old 11th February 2013, 10:42 PM   #5
diyAudio Member
 
Join Date: Aug 2008
Location: Broomfield, CO
Sorry to temporarily hijack this thread but I have a question for JohnAtood.

John, what is your preferred method to determine the input impedance of an output transformer? Is there a more accurate method than using the turns ratio?
  Reply With Quote
Old 11th February 2013, 11:52 PM   #6
diyAudio Member
 
the_manta's Avatar
 
Join Date: Nov 2006
Location: Munich, Bavaria
Quote:
Originally Posted by sparkydave View Post
Thanks! I was pretty sure it meant plate-to-plate. Interestingly, I stumped one of the electrical engineers where I worked when I wondered if one leg of this 8000 ohm transformer would look like 2000 ohms or 4000 ohms, but when I did the math it would be 2000 ohms as John pointed out. Glad I remember something about transformers from school.
Depends on the conduction angle.
Class A: 4000 Ohms
Class B: 2000 Ohms
__________________
Терпенье и труд все перетрут
  Reply With Quote
Old 12th February 2013, 10:29 AM   #7
N4BBQ is offline N4BBQ  United States
diyAudio Member
 
N4BBQ's Avatar
 
Join Date: Nov 2009
Location: Dahlonega, GA
Quote:
Originally Posted by ronaldw441 View Post
Sorry to temporarily hijack this thread but I have a question for JohnAtood.

John, what is your preferred method to determine the input impedance of an output transformer? Is there a more accurate method than using the turns ratio?
I'm not John, but you can easily measure a transformer's impedance yourself. See the link below.

Measuring the input impedance, bandwidth and efficiency of transformers
  Reply With Quote
Old 12th February 2013, 04:30 PM   #8
diyAudio Member
 
Join Date: Aug 2008
Location: Broomfield, CO
N$BBQ,

Thank you. That's just what I was looking for.

Ron
  Reply With Quote
Old 12th February 2013, 05:37 PM   #9
diyAudio Member
 
JohnAtwood's Avatar
 
Join Date: May 2006
Location: Rural Nevada
Sorry for being away from this thread. N4BBQ's link describes the technique better than I could! One thing I might add is that the choice of RL may have to be an educated guess. For example, if you have a mystery output transformer that has two secondary taps, you have to decide whether they are 4 and 8 ohms or 8 and 16 ohms. Vintage amps often had only 8 and 16, whereas modern tube amps more often opt for 4 and 8. If there are three taps, it is almost always 4, 8, and 16.

- John
  Reply With Quote
Old 12th February 2013, 10:59 PM   #10
N4BBQ is offline N4BBQ  United States
diyAudio Member
 
N4BBQ's Avatar
 
Join Date: Nov 2009
Location: Dahlonega, GA
Quote:
Originally Posted by ronaldw441 View Post
N$BBQ,

Thank you. That's just what I was looking for.

Ron
You're very welcome. I've used that method numerous times to identify scrap transformers.
  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
Silly question! :-) zerokelvin99 Power Supplies 2 6th December 2011 01:20 PM
Is this a silly question? Arizona Dan Digital Line Level 20 15th February 2010 08:02 AM
Silly question A Sanchez Power Supplies 8 19th May 2009 01:37 AM
Silly Question???? Zero Cool Solid State 7 16th October 2004 11:34 AM
A silly question, but... mjarve Solid State 2 3rd August 2004 09:50 PM


New To Site? Need Help?

All times are GMT. The time now is 04:56 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