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 Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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 8th October 2011, 02:32 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 PRO-signal. 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 02:38 AM.
 8th October 2011, 04:54 AM #2 diyAudio Member     Join Date: Feb 2009 Location: Melbourne, Oz This link may help: Cheap Output Transformers
 8th October 2011, 06:58 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 AC-voltage, say 1 V and 1kHz in the 8 ohms secondary and read the voltages from all pirimary outputs and tell us.
 8th October 2011, 12:17 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 12:46 PM.
 8th October 2011, 01:05 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, 02:55 PM #6 diyAudio Member     Join Date: Sep 2008 Use them in a circlotron __________________ Real tubes have top-caps
 8th October 2011, 06:05 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 170-250V range. http://www.hifitubes.nl/weblog/wp-co...ctric-6cw5.pdf
 8th October 2011, 11:46 PM #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, 12:47 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 15-20 used EL86/PL84 tubes. Then I can use a PPP solution to eleminate the low impedance. Benny
 9th October 2011, 01:14 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 200-230V, 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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