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Author Topic: Where to find 1K CT to 8 Ohm audio transformers?  (Read 302 times)

WD8SBB

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Where to find 1K CT to 8 Ohm audio transformers?
« on: August 30, 2022, 02:04:01 AM »

I'm wanting to do some experimenting with audio filtering and could use some "old time" transistor audio transformers for impedance matching and isolation.   

1K ohm center taped to 8 ohm 

73 and TIA
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K0RO

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Re: Where to find 1K CT to 8 Ohm audio transformers?
« Reply #2 on: August 30, 2022, 08:24:39 AM »

Chances are a 110v to 6.3 v filament transformer would do the job.  The trick would be finding one with a center-tapped primary.  Check out this website to calculate other possible configurations. I based my comment about the filament transformer on the formula therein.  ...assuming I did the math correctly  ;)
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W9IQ

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Re: Where to find 1K CT to 8 Ohm audio transformers?
« Reply #3 on: August 30, 2022, 08:37:54 AM »

Chances are a 110v to 6.3 v filament transformer would do the job.  The trick would be finding one with a center-tapped primary.  Check out this website to calculate other possible configurations. I based my comment about the filament transformer on the formula therein.  ...assuming I did the math correctly  ;)

The turns ratio for a 120 V to 6.3 V transformer is 120/6.3 = 19. The impedance transformation ratio is the square of the turns ratio 192 = 361. The impedance transformation ratio of a 1000 ohm to 8 ohm transformer is 1000/8 = 125. So I don't think this is a close substitute. A 120 volt to 12 volt transformer would be very close, at least from an impedance ratio.

- Glenn W9IQ
« Last Edit: August 30, 2022, 08:40:22 AM by W9IQ »
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

K0RO

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Re: Where to find 1K CT to 8 Ohm audio transformers?
« Reply #4 on: August 30, 2022, 09:57:37 AM »

Glenn, thanks.  Hence my caveat re the math ;)
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W1VT

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Re: Where to find 1K CT to 8 Ohm audio transformers?
« Reply #5 on: August 30, 2022, 11:02:26 AM »

10pcs 1300: Audio Transformer 8 Ohm Transformer EE14 POS Transformador

At ten for  $12 on eBay, I'd figure out how to make it work while waiting for it to arrive from China.
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W9AC

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Re: Where to find 1K CT to 8 Ohm audio transformers?
« Reply #6 on: August 30, 2022, 11:28:19 AM »

This transformer is close to what one would find in a ca. 1960s AM transistor radio's output stage.  It's rated for 200 mW and a +/-3dB response of 300 Hz to 3.4 kHz:

https://www.mouser.com/ProductDetail/Xicon/42TM013-RC?qs=h3Xc2LqAealCgSV7Tuf2oQ%3D%3D

Or, dig one out of an old 9V transistor radio. 

This transformer would be good to just under 1W of audio power with better distortion and response characteristics, but more $$$:

https://www.mouser.com/ProductDetail/Hammond-Manufacturing/146K?qs=cEOXnW3%2Fj38rUsAZF%252B7esQ%3D%3D

Paul, W9AC
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W9FIB

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Re: Where to find 1K CT to 8 Ohm audio transformers?
« Reply #7 on: September 02, 2022, 02:48:43 AM »

Was on the HAMMOND web site the other day and saw they have a line up of audio transformers. W9AC references them through a reseller. Just saw that.

FWI they are also making Dahl transformers for many old amps and rigs.
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73, Stan
Travelling the world one signal at a time.

KD6VXI

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Re: Where to find 1K CT to 8 Ohm audio transformers?
« Reply #8 on: September 02, 2022, 09:58:29 AM »

Was on the HAMMOND web site the other day and saw they have a line up of audio transformers. W9AC references them through a reseller. Just saw that.

FWI they are also making Dahl transformers for many old amps and rigs.

They make some Dahl iron.  They had a problem where they couldn't get all the designs off a hard drive Jeff had supplied (the original purchaser of Dahl after he went SK).  Those designs I believe where finally able to be deciphered.  They where making all his iron for a period of time.  Then they dropped some (a lot) of them again.

I believe Hammond doesn't want to compete with inferior products that are available today.  EPD is supposed to be a Dahl substitute, but they aren't. They make voltage, they make current.  But they sure don't make the KVA the original Dahl did.

--Shane
WP2ASS / ex KD6VXI
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