SANSUI AU-70 or 1000A??? - 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 2nd August 2012, 01:05 AM   #1
diyAudio Member
 
Join Date: Jun 2009
Default SANSUI AU-70 or 1000A???

Hello everyone.

I have a pair of SANSUI output transformers labeled “AU-70”. I am not certain which amplifier they came from. As far as size and dimensions, my OPTs are comparable to other OPTs that can deliver 30-35W.

First guess would be the Sansui AU70 integrated amp, which uses 7189’s in a PP configuration for the final stage. However, I estimated the transformers’ primary impedance to be 6,300 ohms, which is somewhat low for the 7189’s.

On the other hand, 6,300 ohms is suitable for a final stage using 7591’s in PP as used in the Sansui 1000A amp.

Could anyone, please, clarify the mystery and put an end to my dilemma? I would like to build an amp and use these OPTs, but I am not sure what tubes to use.

Thank you in advance for your help and advice.
  Reply With Quote
Old 2nd August 2012, 03:08 AM   #2
AJT is offline AJT  Philippines
diyAudio Moderator
 
AJT's Avatar
 
Join Date: May 2003
Location: Palatiw, Pasig City
as long as you know the transformer specs you can use them in any project you desire....
__________________
the best advertisement for a good audio design is the number of diy'ers wanting to build it after all the years....never the say so of so called gurus....
  Reply With Quote
Old 2nd August 2012, 03:50 AM   #3
korey is offline korey  United States
diyAudio Member
 
Join Date: Mar 2008
Quote:
Originally Posted by aandre2200 View Post

I have a pair of SANSUI output transformers labeled “AU-70”.
You just answered your own question! They are from the AU-70.
  Reply With Quote
Old 2nd August 2012, 04:10 PM   #4
diyAudio Member
 
Join Date: Jun 2009
@ Tony:

You are absolutely correct. Unfortunately I do not have all the transformer specs. I used a rather empirical method to measure the primary impedance, which is about 6,300 ohm. I have no idea about the power handling capabilities of these transformers. This is why I need to know which amp they came from. I would really hate to fry a pair of perfectly good transformers.

@Korey:

AU-70 is indeed the obvious first guess. However, as I said before, the 6,300 ohm impedance is rather low for the 7189 tubes used in the AU-70 (data sheet indicates a plate to plate resistance of 8,000 ohm, even 10,000 ohm in class AB1 – triode mode). On the other hand, the data sheet for the 7951 tubes used in the 1000A indicates a plate to plate load of 6,600 - therefore my dilemma.

Perhaps someone on this forum has one of these amps and is kind enough to check for me the label on the output transformers?............. It would be greatly appreciated!

Thank you.
  Reply With Quote
Old 2nd August 2012, 08:11 PM   #5
diyAudio Member
 
directdriver's Avatar
 
Join Date: Nov 2005
I have output transformers from the Sansui 1000A receiver and their transformer number is 410-5234 and sometimes they are labeld 1000A and sometimes both numbers are labeled on the end bell. So most likely your transformers are from the AU70 integrated amp which uses 7189 tubes. Although according to this schematic the impedance should be 8K.
Click the image to open in full size.

Does your irons shape like these? Too bad I couldn't find a picture showing the transformer number...
http://images02.olx.com.my/ui/7/65/0...1286515715.jpg
  Reply With Quote
Old 2nd August 2012, 09:14 PM   #6
diyAudio Member
 
Chris Hornbeck's Avatar
 
Join Date: May 2011
Location: Little Rock
We all easily lose sight of the fact that the real working load of an amplifier is a loudspeaker, something very, very far from a resistor. Variations of 25%, that seem so important to us when designing, are *nothing* compared to the real world use. You certainly cannot hurt your transformer by a slight mismatch - if so, they'd all be dead already.

If you want to use them with 6BQ5/EL84's and are concerned with linearity, just keep working voltages down and idling current up, connect as triodes. Not tons of power output, maybe +7 or +8dBW, but clean.

All good fortune,
Chris
  Reply With Quote
Old 2nd August 2012, 11:16 PM   #7
diyAudio Member
 
Michael Koster's Avatar
 
Join Date: Jan 2008
Location: Eureka, CA
What is your empirical method to estimate the primary impedance? I.e. what is the turns ratio and how did you determine it?

Thanks!

Last edited by Michael Koster; 2nd August 2012 at 11:38 PM.
  Reply With Quote
Old 2nd August 2012, 11:59 PM   #8
diyAudio Member
 
Join Date: Jun 2009
@directdriver

Thank you very much for your effort and the detailed information. The schematic you attached shows the OPT impedance as 8K, just as the 7189 data sheet. Judging by the labeling of you 1000A transformers that shows “1000A”, it appears that mine are indeed from an AU-70. I have to get to the bottom of this impedance discrepancy. Could my transformers be shorted? Who knows!!! I bought them as a set including the mains transformer, which was definitely shorted. Thanks again, directdriver!!!


@ Chris Hornbeck

I understand perfectly what you are saying and you are correct. The idea was to figure out if I can get 30-35W out of these babies instead of just 15-17W. Thanks for your input.


@Michael Koster

The method to estimate the primary impedance consisted of multiplying the impedance of each speaker tap with the turn ratio squared (turn ratio different for each of the 4, 8, and 16 ohm taps). Because of measurement inaccuracies, the calculated impedance values ranged between 6,150 and 6,600 ohm, the average being 6,300.
  Reply With Quote
Old 3rd August 2012, 12:09 AM   #9
diyAudio Member
 
Join Date: Jun 2009
By the way, I determined the turn ratio by applying 15, 10, and 5 volts and measuring the voltage on each speaker tap. I did a total of 9 tests, good enough for estimating purposes.
  Reply With Quote
Old 3rd August 2012, 01:09 AM   #10
diyAudio Member
 
Michael Koster's Avatar
 
Join Date: Jan 2008
Location: Eureka, CA
Quote:
Originally Posted by aandre2200 View Post
I made a mistake in my previous post. The average impedace is 6,300 ohm, not 6,600. Sorry.

By th way, I determined the turn ratio by applying 15, 10, and 5 volts and measuring the voltage on each speaker tap. I did a total of 9 tests, good enough for estimating purposes.
One measurement should be good enough under the right conditions: e.g. midband frequency 400 Hz or thereabouts, with a resistive load on the output, and preferably at at least a volt output or more. Also did you observe the output waveform on a scope?

What I'm saying is that low voltage unloaded measurements at certain frequencies could introduce gross voltage errors. Even the simple winding DCR can account for 10% difference in actual turns ratio vs. measured voltage ratio. If the 8K ohms specified includes say 10% DCR (primary plus reflected secondary), and you measure without a load, then your impedance ratio could be off by something like 20%. Add to this a little overshoot due to leakage inductance at low voltage and you may have explained your discrepancy.

In fact, if your most representative measurement was the highest, 6600 ohms, and your DCR component causes a 10% voltage error in an unloaded measurement, you have exactly 8K... Assuming the 8K is measured with the rated load.

Last edited by Michael Koster; 3rd August 2012 at 01:19 AM.
  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
sansui 1000a maintenance dognut Tubes / Valves 1 18th February 2009 12:51 AM
Sansui AU-3900 mot on/off Solid State 18 30th May 2007 04:10 PM
Sansui 1000A output transformers JohnG Swap Meet 7 27th February 2006 10:39 PM
Sansui 1000A OPT's jlsem Tubes / Valves 1 7th July 2005 05:10 PM
Sansui Au-517&au-717 ManUtd Solid State 4 29th March 2004 01:13 AM


New To Site? Need Help?

All times are GMT. The time now is 05:39 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