SE OT impedance question - 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 13th January 2012, 09:16 AM   #1
johi is offline johi  Sweden
diyAudio Member
 
Join Date: Feb 2011
Default SE OT impedance question

Hi,

As newbie in diy world I purchased a pair of SE OT from eBay Germany not knowing much more that they were type S2 (whatever this means) and that theyare suited for SE projects, 4 Ohm out, 4 - 8 W. Seller proposed EL95, ECL86 tubes as candidates.
So I wanted to check impedance of the OT to see which more tubes could be suitable. I fed 16,8 VAC, 50 Hz in and got 0,2 VAC out, which gives turn ratio 84:1. Further calculation gives 28k primary for the 4 Ohm. I do not see how this fits with ECL86 or any other tube.
So please help me to understand 1) where this OT can be used, or 2) what I did wrong when checking turn ratio.
Thanks in advance
John
  Reply With Quote
Old 13th January 2012, 10:29 AM   #2
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
A small transfomer, probably intended for a radio set or guitar practice amp, might not work too well at 50Hz. Measure the primary and secondary inductance (some DMM can do this). The ratio of inductance will be fairly close to the impedance ratio, as both depend on turns squared.

Another issue is that some transformers need some DC through them to boost inductance.
  Reply With Quote
Old 13th January 2012, 02:39 PM   #3
diyAudio Member
 
Tom Bavis's Avatar
 
Join Date: Jun 2002
Location: Macedon NY
If your meter resolves only 0.1V steps (and has a typical accuracy of 0.7% plus or minus a digit) your measurement accuracy is +/- 50%, possibly worse. Use a higher voltage (even 240VAC is NOT out of the question) or a meter with better resolution. Obviously take precautions for safety - connect meter with clips before connecting input. I would expect 6-10K primary.
  Reply With Quote
Old 13th January 2012, 07:01 PM   #4
cerrem is offline cerrem  United States
diyAudio Member
 
Join Date: Jun 2005
Location: San Diego, CA
Place mains voltage across the primary..... Just be cautious...
Then measure the secondary unloaded to obtain the voltage ratio of the windings....I belive you know the rest of the steps...

Chris
  Reply With Quote
Old 15th January 2012, 09:33 AM   #5
johi is offline johi  Sweden
diyAudio Member
 
Join Date: Feb 2011
Thanks for advice. True that transformer does not handle low frequencies well so I used pc sound card as tone generator, attached it to the secondary and measured voltage on primary. Quite as you guys wrote impedance Z=~7,5k for 8 Ohm. Of course neither pc or DMM are wonders of high precision but these two OT are on their way to a small SET.
Thanks again
/John
  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
OT primary impedance calculation cb951303 Tubes / Valves 14 12th April 2013 04:18 AM
Using SE OT for PP. Cassiel Tubes / Valves 10 15th July 2010 10:44 AM
OT/Speaker impedance mismatch Rob11966 Tubes / Valves 3 14th July 2010 07:52 PM
OT impedance problem m0rg Tubes / Valves 2 9th July 2004 04:58 AM
SE used as step down OT redofneck Tubes / Valves 2 7th March 2004 07:26 PM


New To Site? Need Help?

All times are GMT. The time now is 02:54 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