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Old 8th October 2011, 03:32 AM   #1
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Default 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 03:38 AM.
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Old 8th October 2011, 05:54 AM   #2
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This link may help:
Cheap Output Transformers
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Old 8th October 2011, 07:58 AM   #3
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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.
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Old 8th October 2011, 01:17 PM   #4
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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
= ( Uin / Uout) = 100 V / 3,16 V = 31,6.
The impedance ratio is 2 = 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.
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Old 8th October 2011, 02:05 PM   #5
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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
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Old 8th October 2011, 03:55 PM   #6
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Use them in a circlotron
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Real tubes have top-caps
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Old 8th October 2011, 07:05 PM   #7
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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
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Old 9th October 2011, 12:46 AM   #8
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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
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Old 9th October 2011, 01:47 AM   #9
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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
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Old 9th October 2011, 02:14 AM   #10
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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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