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Author Topic: 1000 Ohm Speaker  (Read 67 times)

Sooner

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1000 Ohm Speaker
« on: November 26, 2019, 09:10:51 AM »
Here a video clip of an early 1920's radio speaker that I restored and built a Bluetooth receiver/amplifier for. Back in those days the speakers were connected directly to the output tubes (no output transformer), thus the high impedance.  The Bluetooth board came from China and the replica decal from Peru, both off eBay. Since the amplifier was designed for 8 ohms I needed a transformer to match the 1000 ohm speaker and it turns out a 9V AC adapter had just the right primary/secondary ratio. 
https://www.youtube.com/watch?v=doGrMMZfWn0
Sooner AD1512 Serial No. 001

"Paranoia strikes deep. Into your life it will creep." - Neil Young

Orange

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Re: 1000 Ohm Speaker
« Reply #1 on: November 26, 2019, 09:39:44 AM »
I like how the modern bluetooth interfaces requires a step-up transformer - but the old tube interface is transformerless!

I wonder how the original design prevented the DC bias of the output tube from going into the speaker voice coil.   Did the original design employ the use of some type of balanced design (like an H bridge)?   Doesn't seem like it'd be economical to do so. 


Sooner

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Re: 1000 Ohm Speaker
« Reply #2 on: November 26, 2019, 11:18:57 AM »
I wonder how the original design prevented the DC bias of the output tube from going into the speaker voice coil.   Did the original design employ the use of some type of balanced design (like an H bridge)?   Doesn't seem like it'd be economical to do so.

Beats me. I wonder what voltage was going to the speaker. Could you get a buzz from it?

Also it's interesting that this speaker used a permanent magnet. I wonder why they switched to  "field coil" electromagnets later and then back to permanent magnets. 
Sooner AD1512 Serial No. 001

"Paranoia strikes deep. Into your life it will creep." - Neil Young

 

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