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A New Ultrasonic Heater

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Posted on January 6, 2017 at 19:39:44
Triode_Kingdom
Audiophile

Posts: 5809
Location: Texas
Joined: September 24, 2006
I've been working on a revised circuit for this in my spare time. The design below is the result. It may look complex, but it's really only a small handful of parts, and it could be built on a very small circuit board. The output transformer can be wound to produce exactly the voltage needed for tubes like the 211 and GM-70. An additional, external transformer can be added for tubes that need 2.5V or 1.5V.

To explain the operation, this circuit is powered by +160V produced by a bridge rectifier/filter attached directly to the AC mains. When power is turned on, the startup circuit supplies about +5.5V to the comparator, sufficient to start the oscillations. A VCC winding on the transformer then produces a rectified voltage that takes over from the startup circuit and operates the comparator at full power, about +10V. Not shown, a 2A fuse between the +160V source and the primary of the output transformer protects the components from overload if oscillation ceases or the output is shorted. This circuit will oscillate at frequencies to at least 200kHz, depending on the RC values at the comparator.

This circuit was interesting to design, but to be honest, I don't have a lot of interest in building it myself. My SETs operate satisfactorily on the halogen units, and I don't plan to use ultrasonic heating on drivers or preamps. Any engineer interested in pursuing this should be able to take it from here. I modeled the circuit using a LT1713 differential comparator and IPB65R420CFD MOSFET, both included in the latest version of LTspice IV.





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RE: A New Ultrasonic Heater, posted on January 6, 2017 at 21:07:03
deafbykhorns
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Posts: 650
Location: Florida
Joined: October 17, 2003
If there's some interest, I might take on the circuit board design. Im not a EE by law but have made some gerber files in the past, there's a couple sites that also have some online software to produce a simple circuit board.
Attach the spice file and I'll search for some transformers, do some testing and put together a mouser job file. My window is Jan-March, or until fishing season starts....

 

RE: A New Ultrasonic Heater, posted on January 7, 2017 at 07:42:24
Triode_Kingdom
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Posts: 5809
Location: Texas
Joined: September 24, 2006
E-mail sent.

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Buy Chinese. Bury freedom.

 

RE: A New Ultrasonic Heater, posted on January 7, 2017 at 08:36:12
vinnie2
Audiophile

Posts: 2520
Joined: September 28, 2013
You might get a nice little side business going if you built and sold.

 

RE: Maybe if we were retired, posted on January 7, 2017 at 15:26:59
deafbykhorns
Audiophile

Posts: 650
Location: Florida
Joined: October 17, 2003
I'm sure Jack's daytime job pays more....I know mine does.
Besides, its just a hobby and fun for the rest of us.

 

RE: A New Ultrasonic Heater, posted on January 7, 2017 at 16:22:51
deafbykhorns
Audiophile

Posts: 650
Location: Florida
Joined: October 17, 2003
Thanks, I'll order some parts in the next week and start some bread boarding.
That MOSFET you chose looks robust enough to power our transmitting tubes.
The step down may be the tricky part, probably need to go custom.

 

Output Transformer, posted on January 7, 2017 at 17:58:13
Triode_Kingdom
Audiophile

Posts: 5809
Location: Texas
Joined: September 24, 2006
Before proceeding, I want to caution you and anyone else reading this about the lethal voltages involved. In addition to the usual precautions necessary when working with tube-type equipment, I urge you not to work with a circuit of this type without using an isolation transformer. "ONE HAND IN YOUR POCKET" WON'T PREVENT ELECTROCUTION if the circuit is powered directly from the AC mains without a transformer. Please remember this. It only takes a moment's distraction or inattention to be seriously injured or killed, and the risk is MUCH greater without an isolation transformer.

"The step down may be the tricky part, probably need to go custom."

The toroidal output transformer from the halogen lighting unit will work fine. It should output the same voltage as in the original design, roughly 30V pk-pk. I don't recommend attempting to perform the entire step-down to 2.5V or 1.5V in one transformer. The advantage of the new design (in addition to higher frequency) is that it will oscillate with no load. This allows attaching a second transformer onto the first for the final step-down. FWIW, the use of multiple transformers is a normal and accepted approach in broadband RF work for higher ratios, meaning anything more than about 4:1. I don't think it's possible to transform a 160V square wave to 2.5V in one transformer without losing considerable efficiency. That's a 64:1 ratio. Accomplishing this even with two transformers at 8:1 each can be tricky and may require transmission line techniques (multifilar windings) for good efficiency. Did you see my earlier post linking to the green cores? That's what I would use for the external transformer. Also, bear in mind that the first transformer is the only thing providing isolation between the output of the unit and the AC mains. It needs reliable, heat-resistant insulation between primary and secondary. Requirements for the second transformer aren't quite so rigorous.




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Buy Chinese. Bury freedom.

 

RE: Maybe if we were retired, posted on January 7, 2017 at 17:59:06
vinnie2
Audiophile

Posts: 2520
Joined: September 28, 2013
We are talking extra income here, not full time. Help pay for the audio hobby type of thing.

 

RE: Output Transformer, posted on January 9, 2017 at 17:44:43
deafbykhorns
Audiophile

Posts: 650
Location: Florida
Joined: October 17, 2003
The second transformer works fine, I tried it with the halo supplies and it works fine. I got about 1.6v with the second toroidal playing around with the windings.

Your circuit seems to work with a 24-48v rectified supply at the primary which would give some isolation and lower the voltage. Its not a perfect sq. wave but looks better than the Halo.

As triode_kingdom said, use an isolation transformer whenever possible as an extra precaution.

 

RE: Output Transformer, posted on January 10, 2017 at 05:38:23
Triode_Kingdom
Audiophile

Posts: 5809
Location: Texas
Joined: September 24, 2006
Do you mean that you added an external transformer to the "standard" halogen supply? Mine wouldn't oscillate when I did that. Can you provide a few more details about the transformer and the work that was done?




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Buy Chinese. Bury freedom.

 

RE: Output Transformer, posted on January 10, 2017 at 06:56:25
TomWh
Audiophile

Posts: 624
Location: Tucson Az
Joined: August 7, 2003
I am with Triode. Would love to see a schematic with values and transformers you used.

I was wondering, because there are many halogen transformers out there, if using a additional step down might work on some if you loaded it with minimum rating?

Thanks Tom

 

RE: A New Ultrasonic Heater, posted on January 10, 2017 at 16:17:50
megasat16
Audiophile

Posts: 196
Location: SoCal
Joined: April 15, 2015
HF heating is an interesting concept and I think this would work better than the Halogen transformers on it's own.

I recall seeing an article in the VTV magazine before so I tried looking for it. VTV issues 15 has something similar called RF powered amplifier by John Atwood (of One Electron) and the results were interesting to read.



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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: Maybe if we were retired, posted on January 11, 2017 at 07:47:24
vinnie2
Audiophile

Posts: 2520
Joined: September 28, 2013
It's just a hobby and fun for me too. Just because I am retired doesn't mean I have nothing else to do, far from it. It just means I usually get to choose the time I want to do things.

 

Pete Millet design!!!, posted on January 11, 2017 at 08:26:21
TomWh
Audiophile

Posts: 624
Location: Tucson Az
Joined: August 7, 2003
Read through the VTV article it was interesting. Also ran across Pete Millet design on his web site. His sine wine on 100k looks impressive. They also did some good listening tests.

It is going to cost a little more and of course you have to bread board it but that 15 year old design looks pretty good if a sine wave makes a real difference.

Well I hope the smart sand guys will keep this going maybe the holy grail is down this ave???

Enjoy the ride
Tom

 

RE: Output Transformer, posted on January 12, 2017 at 04:29:33
deafbykhorns
Audiophile

Posts: 650
Location: Florida
Joined: October 17, 2003
I just used another tube behind the first TX to get it oscillating.
Not practical but got the job done.

 

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