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8th October 2011, 03:32 AM  #1 
diyAudio Member
Join Date: Jan 2005
Location: Denmark

100 V OPT
Hey
I was up in landfills, where I bought a pair of used speakers in their hand shop. The speakers are damaged but there was a transformer at each speaker box. After I have googlet a little I found out it was 100 V types from PROsignal. I found a data sheet here: http://www.farnell.com/datasheets/483955.pdf type is PO38A. How do I measure the primary impedance so I can use them in a little tube amp. Benny Last edited by Hojvaelde; 8th October 2011 at 03:38 AM. 
8th October 2011, 05:54 AM  #2 
diyAudio Member
Join Date: Feb 2009
Location: Melbourne, Oz

This link may help:
Cheap Output Transformers 
8th October 2011, 07:58 AM  #3 
diyAudio Member
Join Date: Feb 2010

What version ( power ) is your transformers ?
Try first to determine the turns (transforming) ratios available with different primaries. Feed a known ACvoltage, say 1 V and 1kHz in the 8 ohms secondary and read the voltages from all pirimary outputs and tell us. 
8th October 2011, 01:17 PM  #4 
diyAudio Member
Join Date: Feb 2010

Let's calculate an example based on the specification you linked.
We know that there is constant voltage 100 V at the primary. If we select the primary taps for 1.25 W and 8 ohms secondary. We can now calculate the voltage across the secondary. This is: U = √ P x R, which is √ 1,25 W x 8 ohms = 3,16 V. Then we can determine the transforming ratio µ = ( Uin / Uout) = 100 V / 3,16 V = 31,6. The impedance ratio is µ2 = 1000 and finally the reflected impedance from 8 ohms secondary to 1.25 W primary = 1000 x 8 ohms = 8 kilo ohms. For 2.5 W primary, the reflected impedance is 4 k and for 5 W primary it is 2 k. etc. Last edited by artosalo; 8th October 2011 at 01:46 PM. 
8th October 2011, 02:05 PM  #5 
diyAudio Member
Join Date: Jan 2005
Location: Denmark

Yargh
Those 100 trafoes have a Zaa at only 1k. (8 ohm on 8 ohm tap) The tabs are named Com, 40watt, 30watt, 20watt and 10watt. Using 40 watt as B+ and COM and 10W for plate connections. Are they useless or what What tube can use so low impedance? Benny 
8th October 2011, 03:55 PM  #6 
diyAudio Member
Join Date: Sep 2008

Use them in a circlotron
__________________
Real tubes have topcaps 
8th October 2011, 07:05 PM  #7 
diyAudio Member
Join Date: Apr 2010

Put a 16 ohm speaker on them and use a couple of EL86's for around 25W. Or double up the output and 50W into 8 ohms, going to need a 1:1 power transformer with a decent amount of current as the tubes run in the 170250V range.
http://www.hifitubes.nl/weblog/wpco...ctric6cw5.pdf 
9th October 2011, 12:46 AM  #8 
diyAudio Member
Join Date: Feb 2009
Location: Melbourne, Oz

Benny, which part number do you have?
"Using 40 watt as B+ and COM and 10W for plate connections"  I think you may have misinterpreted the use of these line transformers. Ciao, Tim 
9th October 2011, 01:47 AM  #9 
diyAudio Member
Join Date: Jan 2005
Location: Denmark

Hi
"Using 40 watt as B+ and COM and 10W for plate connections" I meant: Using "40 watt" tap as B+ and the two taps "COM" and "10Watt" as plate connections. This gives Raa at 1k and the impedance from B+ to "COM" and "10 Watt" are indentical. Yes I know that they are not designed for use in tube amplifiers, but there are a number of articles showing that they can be used. See the link in your first post. Unfortunately mine is not as useful as other types. I have 1520 used EL86/PL84 tubes. Then I can use a PPP solution to eleminate the low impedance. Benny 
9th October 2011, 02:14 AM  #10 
diyAudio Member
Join Date: Feb 2009
Location: Melbourne, Oz

Appologies  I misinterpreted your post and thought you had a 5W tapping.
Philips made many PA amps using 6CM5/EL36  they have a relatively low PP impedance requirement  which could probably allow 1k PP with B+ and screen around 200230V, from a quick peruse of the datasheet. I have a restored quad 6CM5 amp, which worked out quite well. Ciao, Tim 
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