testing for the ratios on old opt's - 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 7th June 2009, 10:16 AM   #1
diyAudio Member
 
aardvarkash10's Avatar
 
Join Date: Mar 2007
Location: Auckland, NZ
Default testing for the ratios on old opt's

problem - I have a sackful (well, a dozen pairs) of old se and pp opt's. Look similar to the small hammond and edcor open-frame jobbies, and mostly recovered from old consoles and the like.

To be really useful, it would be good to know their electrical specs - winding and inductance ratio, max DC current, etc.

I figured, hook the secondary side to a 50hz low voltage supply and measure what comes off the primaries to get a ratio. So, using a 230v-12v 4A halogen lighting transformer (a real one, not a switch mode) I have proceeded.

First few seemed ok - small pp units with between 30:1 and 60:1 voltage ratios @ 50hz.

BUT - I'm getting distinctly odd readings on some of the se units, and I'm beginning to doubt my reasoning.

Am I missing something here? Do I have a problem because I am using a 50hz cycle and the trannies aren't able to deal with that?

And more to the point, how whould YOU do this, in the absence of a reliable signal generator or 'scope?
__________________
"Folks, you can't prove truthiness with information. You prove truthiness with more truthiness. In a process known as truthinessiness." - Stephen Colbert, The Colbert Report
  Reply With Quote
Old 7th June 2009, 10:47 AM   #2
diyAudio Member
 
Steerpike's Avatar
 
Join Date: Jan 2006
Location: Johannesburg, South Africa
SE transformers have an airgap in the core, which will make them behave 'oddly' as they near saturation. You'd need to energise them at lower voltages. 12V into the seondary might be a bit much for them.
__________________
Steerpike's Toybox
  Reply With Quote
Old 7th June 2009, 11:21 AM   #3
diyAudio Member
 
Ty_Bower's Avatar
 
Join Date: Mar 2007
Location: Newark, DE
You're on the right track. I usually stick the 12 volt supply on the primary side instead. You'll only get a few tenths of a volt out the secondary, but most meters are good enough to provide useful data. Here's some notes on one I measured:

http://www.diytube.com/phpBB2/viewto...t=3180&start=1
  Reply With Quote
Old 7th June 2009, 03:36 PM   #4
Stixx is offline Stixx  Germany
I am
diyAudio Member
 
Stixx's Avatar
 
Join Date: Sep 2003
Location: Southern Germany
Funny...
I just did that on an old Saba SE-OPT from one of their "famous" radios.
I am planning to use them in a headphone amp. Putting around 9V
from a small heater transformer on one of the windings gave me a clue on the winding ratio
(what will be something like a 6K:300R impedance ratio).

PS. Of course i have two of them...

  Reply With Quote
Old 7th June 2009, 04:00 PM   #5
diyAudio Member
 
Michael Koster's Avatar
 
Join Date: Jan 2008
Location: Eureka, CA
Quote:
Originally posted by Steerpike
SE transformers have an airgap in the core, which will make them behave 'oddly' as they near saturation. You'd need to energise them at lower voltages. 12V into the seondary might be a bit much for them.

Agreed. Applying 12V RMS to the 8 ohm output of an OPT generates
the equivalent signal voltage of an amplifier operating at 18watts
output power. This would take a pretty big SE OPT not to saturate.
Plus, your step down transformer might put out more than 12V when
lightly loaded as in your test. The formula is E^2/R where E is the
RMS signal voltage and R is the design Zout of the transformer.
12^2/8 = 18 watts. 50 Hz should be fine for most OPTs at lower
voltages. I think using ~12V on the primary is a great suggestion
if that's all you have. Measure the actual primary voltage with your
meter, of course.

Cheers,

Michael
  Reply With Quote
Old 7th June 2009, 07:30 PM   #6
diyAudio Member
 
aardvarkash10's Avatar
 
Join Date: Mar 2007
Location: Auckland, NZ
Default thanks guys

saturation, as I suspected...

THanks for the great tips!
__________________
"Folks, you can't prove truthiness with information. You prove truthiness with more truthiness. In a process known as truthinessiness." - Stephen Colbert, The Colbert Report
  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
Ratios for internal dimensions of speaker box bm_mode Multi-Way 6 18th July 2008 09:06 PM
Irrational ratios/enclosure dimensions Vikash Multi-Way 26 17th December 2005 06:03 AM
s/n ratios curtis73 Car Audio 11 17th December 2003 02:03 AM
Golden ratios and standing waves Vikash Multi-Way 36 27th September 2003 02:12 AM


New To Site? Need Help?

All times are GMT. The time now is 09:22 PM.


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