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Author Topic: Audio output transformer for AA5 etc.  (Read 6401 times)
N3QE
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Posts: 2097




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« on: May 27, 2014, 09:07:26 AM »

I'm looking for a source for a "low-fi" audio output transformer as would've been used in an AA5 set or any tube radio at the very low watt level to drive an 8 ohm or 16 ohm speaker.

I think Radiodaze used to sell cheap low-fi AA5 output transformers but I cannot find them on their website. I do find the Hammond 144 series which seems too pricey to be a cheap AA5 audio output transformer.

Maybe the cheapest choice is to cannibalize a basket-case AA5.
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KD0REQ
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« Reply #1 on: May 27, 2014, 09:19:18 AM »

when all else fails, try one of these for 7 bucks.

http://www.parts-express.com/70v-15w-line-matching-transformer--300-039

antique radios forums suggest at full power, the cores saturate from DC impression, but since the AA5 used 3 to 5 watt output tubes, it should do the job.  impedance may be a hair off, use the lowest tap for the speaker output.  most of those AA5 tubes wanted to look at 4000 to 5000 ohm impedance.  some wanted 2500, which would make this a better match.  if not, change output taps for max volume.
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N2LXM
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« Reply #2 on: May 27, 2014, 09:47:16 AM »

Try a Small 6.3 volt filament transformer. For AA5 with a 50C5 output tube it's close enough.
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AA4PB
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« Reply #3 on: May 27, 2014, 10:05:44 AM »

For a tube type output transformer the impedance match is only one issue. You also need to make sure that the primary winding is able to handle the high voltage to ground and the DC current.
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WX7G
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« Reply #4 on: May 27, 2014, 02:09:27 PM »

Antique Electronic Supply might have the transformer you need.

     http://www.tubesandmore.com/products/transformers_chokes
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W8AAZ
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« Reply #5 on: May 27, 2014, 05:28:53 PM »

Yea, you could can. one.  If you work on old radios,  eventually you will have chassis setting around with parts on them, often with the output transformer and speaker.  The trans do not seem to be bad in my experience.  Usually it is something else that scraps them, like bad IF transformers, or some unique to radio part.  Or just damage and rust.  Ask around to other radio or ham types and I would be surprised if no one has a junker table radio chassis.  That is probably worth waiting for if you want to save money.  New trans for tube/radio audio these days are for a niche market and priced beyond what they seem to be worth, to me.    Especially with my junkpile.  IF you know the radio model you can even look up a schematic to see what sort of tube it was used with, probable power level, and speaker impedance rating, such as on Nostalgia Air.  Don't overlook other tube type junk, such as busted old tube type small record players, or intercoms, etc.
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KG8LB
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« Reply #6 on: May 28, 2014, 04:22:33 AM »

For a tube type output transformer the impedance match is only one issue. You also need to make sure that the primary winding is able to handle the high voltage to ground and the DC current.


  This is an All American 5 tube . The voltages and currents are well within the ratings of most small filament transformers . I have seen them used in the past for just this purpose .
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QRP4U2
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« Reply #7 on: May 28, 2014, 08:22:00 PM »

The Bogen T-725 is a universal output transformer.

Also, one could use a

http://www.tubesandmore.com/products/P-T31

Phil - AC0OB
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KC5LY
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« Reply #8 on: June 09, 2014, 04:40:04 AM »

Filament transformers have been used for replacements in AA5 sets for years. Another source is a vertical output transformer from a tube type television chassis if you can locate one.

Joe
KC5LY
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KH2G
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Posts: 243




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« Reply #9 on: June 14, 2014, 12:40:36 PM »

Any of the old "kitchen" radios output transformer wouild work. Most of them used a 50c5 for output tube. Check the local dump.
regards,
Dick KH2G
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WA2ISE
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Posts: 123




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« Reply #10 on: June 19, 2014, 12:39:32 PM »

I'm looking for a source for a "low-fi" audio output transformer as would've been used in an AA5 set or any tube radio at the very low watt level to drive an 8 ohm or 16 ohm speaker.

...

Maybe the cheapest choice is to cannibalize a basket-case AA5.

Most AA5 radios used speakers of 3.2 or 4 ohm impedance, rarely 8 ohms.  However, if you cannibalize an old AA5 radio, you may be able to use its speaker along with the transformer.  But here I'm assuming you are looking to repair an AA5 type radio set, maybe one of those SW radios sold for novices back in the early 60's. 
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