Identifying output transformer leads - 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 22nd April 2009, 10:07 PM   #1
diyAudio Member
 
Join Date: Jan 2009
Question Identifying output transformer leads

Hi...once again thanks to all of you who have so freely offered your knowledge to this noob..I sucessfully built my first amp from scratch. Couldn't have done it without all your help !
Here's my question: I have and OT that I pulled from an Allied phono/mic amp a while back. I believe it is from the 1940s as there are no IEC codes or any other markings on it. I foolishly did not label the leads, as I hadn't planned on using it, but now I am going to give it a go. I know...lack of foresight on my part. The pimary is easy...2 plates and a CT...but the secondary has 7 taps including the common. I know they are: 4, 8, 16 ohm, and I believe 250 ohm and 70 volt? I know which is the common...the only black lead, but how do I deceipher the others? Physically, the 4 ohm would be the first off the bobbin no ? Then 8 and 16 ohm respectively? I just don't want to hook up a speaker to the other wierd taps and cook it. Any help would be greatly appreciated !!!

P.S. I guess that I should add that this OT was for a pair of 6V6s in cathode bias, with a 5Y3 rectifier.
  Reply With Quote
Old 22nd April 2009, 11:22 PM   #2
diyAudio Member
 
Join Date: Oct 2004
Location: Adelaide South Oz
Multimeter on Ohms will tell the tail.
More turns on the secondary means more winding resistance means higher impedance tap.
So measure from the common.
Wire with lowest resistance to common will be 4 Ohm tap.
Next highest resistance will be 8 Ohm etc.
Cheers,
Ian
  Reply With Quote
Old 22nd April 2009, 11:23 PM   #3
diyAudio Member
 
HollowState's Avatar
 
Join Date: Aug 2006
Location: Taxland, New Jersey
Assuming the secondary is a single tapped winding, not multiple windings, you could use an ohmmeter to measure incremental increases in the DC resistance, You will need a good meter, preferably digital, and one that uses a constant current source like the better HP's or Keithley's. Also one that is comfortable in the sub ohm range. Many cheap battery operated meters are difficult to interpret at very low ohms, but they can serve if you are familiar with it. Good tight connections are necessary.

Lacking this, you could connect the primary to a low level AC voltage source and then measure the incremental secondary voltage. If you use a low voltage for the primary, you will need a good AC level meter that is comfortable with fractional voltage. If you have access to an oscilloscope, that will show low levels quite well.

Since the transformer can withstand higher voltage on the primary, you can go as high as 120 volts to get the secondary output to a more convenient level. Use an isolation transformer if you chose this method and be carful with the connections.
__________________
"It is hard to imagine a more stupid or more dangerous way of making decisions than by putting those decisions in the hands of people who pay no price for being wrong." ~Thomas Sowell
  Reply With Quote
Old 22nd April 2009, 11:56 PM   #4
diyAudio Member
 
Join Date: Jan 2009
Gingertube: Thanks...I kind of figured I could use that type of deduction to deceipher the OT. I just wondered how to identify the wierd taps...i.e. 70v and that. I did use my multimeter and two of the taps read exponentially higher than the rest. Can I assume these are the 250 ohm and 70v taps? Also, where should I find continuity between taps ? I guess all of them since they share common windings, right?
Hollowstate: So you're saying I can hook the primary to say a variac set low and mesure voltage differences between the taps...from common to individual taps? I would hook the two plate leads to the AC source? Then I would need to be careful of the CT , huh?
  Reply With Quote
Old 23rd April 2009, 12:13 AM   #5
diyAudio Member
 
HollowState's Avatar
 
Join Date: Aug 2006
Location: Taxland, New Jersey
Quote:
Originally posted by bereanbill

Hollowstate: So you're saying I can hook the primary to say a variac set low and mesure voltage differences between the taps...from common to individual taps? I would hook the two plate leads to the AC source? Then I would need to be careful of the CT , huh?
You got it!
__________________
"It is hard to imagine a more stupid or more dangerous way of making decisions than by putting those decisions in the hands of people who pay no price for being wrong." ~Thomas Sowell
  Reply With Quote
Old 23rd April 2009, 04:37 AM   #6
rlschow is offline rlschow  United States
diyAudio Member
 
Join Date: Dec 2007
Here's something you should read
http://www.radioremembered.org/outimp.htm
  Reply With Quote
Old 24th April 2009, 01:44 AM   #7
diyAudio Member
 
Join Date: Jan 2009
rlschow..THANKS...that's a great bit of info. I will print it out for future reference.!!!
  Reply With Quote
Old 24th April 2009, 02:27 AM   #8
Vargas is offline Vargas  United States
diyAudio Member
 
Join Date: Apr 2008
Location: Michigan
Here's some more reading. http://www.angelfire.com/electronic/...nsformers.html
It's long but for more of what you are looking for, scroll down to the bottom of the page. Cheers
__________________
When you got'em by the ball's their heart's and mind's will follow!
  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
Steel Leads and Tinned Copper Leads impsick Parts 0 19th April 2009 10:01 AM
Help identifying Output transformer georgepw Parts 2 4th March 2009 08:02 AM
Help identifying transformer? dclapp Parts 2 2nd May 2007 01:28 AM
Identifying output tx. Trebla Tubes / Valves 3 29th September 2006 10:16 PM
Long output lead or long output transistors leads? which one to pick? chris ma Everything Else 3 6th June 2003 12:06 PM


New To Site? Need Help?

All times are GMT. The time now is 03:48 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