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Old 13th January 2011, 06:06 AM   #1
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Default Transistorised-Tubed-Magnetic Amplifier

Hey gang!

Here is my Transistorised-Tubed-Magnetic Amplifier Idea.

As I sifted though my computer tonight, I found my old magnetic amplifier research and dormant plans to build a MAG-AMP based audio amplifier. So I resurected the mag-amp papers and diagrams. This morning I totally redrew Nile Steiner's diagram as it was sloppy. I made some minor circuit changes. I believe the MAG-AMP Mr. Steiner recreated was from some old Navy book, and that was a single-ended one? Anyways I kept it mono for modding by others who choose to double it and make stereo.

I was looking for an apropriate HF AC power supply for this and asked around and I didn't find what I liked. Amazingly just tonight I found exactly what I wanted in my own collection of files, on my HD! I'd downloaded it five years ago and forgot about it. Wow.

Originally it was a chunky transistor inverter circuit to run a flyback transformer and produce HV/HF AC output. I put on my idea cap and completly redesigned the circuit. I had to drew a totally new diagram of it by hand with MS paint. It was grossly drawn in the first place years ago, then saved in JPG format which made it look just like bird ****.
It wouldn't "fit" with my neatly drawn MAG-AMP diagram at all. I redesigned the circuit, made it a two transistor HF AC supply delivering 40khz AC at 12v for the MAG-AMP circuit. The MAG-AMP circuit also needed 12v DC for the bias portion.
So I used a rectifier tube to change the 12v AC @ 50hz to 12v DC. The transformer has windings for the 6.3v AC tube heater.

This is just an interesting, funky chunky little piece of vintage hybrid tech. It is probably inefficent and stuff like that, but thats not the point; this was made just for fun with the tube, transistor, history buffs in mind.

I worked hard and too long right into the early morning hours. I admit I am quite "green" so if there are flaws in the PS section it is mine. Truthfully I am having trouble making the tube section. I don't knw if the input to the tube has to be highvoltage and the DC output of the tube would have to be put though a power resistor to get the 12v DC thats wanted.

I am open to ALL constructive critisism, ideas, circuit change ideas, improvments. Just not talk that this is pointless obsolite inefficent tech. Thanks, I hope you like my drawing and my idea!


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Last edited by CivicProtection; 13th January 2011 at 06:15 AM.
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Old 13th January 2011, 08:25 AM   #2
Arnulf is offline Arnulf  Europe
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Have you considered using stepper motor as your HF AC source in order to avoid transistors alltogether ? I used to tinker with the idea of making a magamp and even have the motor ready (it's one of those beasts from large printers and/or plotters, 200 or 400 steps per revolution I believe), I gave up at building a suitable magamp iron itself.
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mod verb, transitive /mod/ to state that one is utterly clueless about the operation of device to be "modded" and into "fixing" things that are not broken; "My new amplifier sounds great so I want to mod it."
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Old 13th January 2011, 08:52 AM   #3
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OK. I took another stab at this: I redesigned the circuit and redrew the diagram....AGAIN. Replaced the tubed power supply in favor for a solid-state bridge rectified one.

Obviously solid-state supply simplifies things, and I really don't have the hang of designing a tube powersupply. I saw errors in my tube power supply I don't understand how to repair.

In redesigning the circuit; I figured out a NEW ground rail that links the sections together properly.

At the moment; I am worried about bias power sneaking back though the circuit to the audio input source. Possible?

Mr. Steiner used generic farite toroids for his audio MAG-AMP.
I don't really see why standard transformers wouldn't work.
However I think the idea is that the rings would work better but the normal ones would still work.

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Last edited by CivicProtection; 13th January 2011 at 08:57 AM.
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Old 13th January 2011, 09:13 AM   #4
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Quote:
Originally Posted by Arnulf View Post
Have you considered using stepper motor as your HF AC source in order to avoid transistors alltogether ? I used to tinker with the idea of making a magamp and even have the motor ready (it's one of those beasts from large printers and/or plotters, 200 or 400 steps per revolution I believe), I gave up at building a suitable magamp iron itself.
No, I am not interested in that aproach at all. Transistors are fine by me.
Tube would be more retro and interesting though.

In regards to giving up: if you think you can, you CAN. If you think you can't; you're right!

MAG-AMP based audio systems HAVE been built before. You can find SUCCESSFUL home-brewed MAG-AMP's on youtube. It has been built with expensive setups and its been built with junk. You had NO good reason to "give up". The information is out there to find.
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Old 13th January 2011, 09:28 AM   #5
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I was looking at a diagram explaining various charactoristics of audio MAG-AMP's
There is a diagram which closely matches the design I have used and the article said it was a "push-pull" amp? So this design I have made is NOT either a class A or a "single ended".
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Old 13th January 2011, 12:31 PM   #6
Arnulf is offline Arnulf  Europe
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There is nothing "pushing" or "pulling" the output, there is only one device doing the output work so how can it be a push-pull ?


I need to locate a suitable magamp (= the iron involved) in order to proceed any further. That's the part I gave up on, it just happens to be crucial to get things working The improvised magamp I wound on salvaged ferrite E-I core with oscillator + power MOSFET driver as the AC source started buzzing and the driver was overheating, indicating inductance was faaaaar from what I anticipated. I have everything else ready though.

Now that you reminded me again of this, I think I'm going to try my "HF generator" and see how it works while I still have a DSO (borrowed to help me fix problems with guitar amplifier I'm building, described in another thread) at my disposal.
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mod verb, transitive /mod/ to state that one is utterly clueless about the operation of device to be "modded" and into "fixing" things that are not broken; "My new amplifier sounds great so I want to mod it."
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Old 13th January 2011, 05:25 PM   #7
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Originally Posted by Arnulf View Post
There is nothing "pushing" or "pulling" the output, there is only one device doing the output work so how can it be a push-pull ?


I need to locate a suitable magamp (= the iron involved) in order to proceed any further. That's the part I gave up on, it just happens to be crucial to get things working The improvised magamp I wound on salvaged ferrite E-I core with oscillator + power MOSFET driver as the AC source started buzzing and the driver was overheating, indicating inductance was faaaaar from what I anticipated. I have everything else ready though.

Now that you reminded me again of this, I think I'm going to try my "HF generator" and see how it works while I still have a DSO (borrowed to help me fix problems with guitar amplifier I'm building, described in another thread) at my disposal.
Sorry if I was harsh, but I have little patience for those who give up totally. But I am sincerley pleased that you are back in the game. I have collected a bunch of mag-amp books, related information, a TON of tube books, all kinds of goodies. If you like, you can have some of it to help you in your venture. PM me.

By the way; this HF generator you mentioned. Remindes me that Tesla had a HF alternator with MANY poles on it. Here is the patent number if you feel like looking it up. 447920
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Old 13th January 2011, 06:02 PM   #8
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I attempted to obtain a copy of "Magnetic Amplifiers A Rising Star in Naval Electronics"
the one from around 1951. It is apaerently the base for some later mag-amp books and full of useful information. I was looking for the full copy, not parts of it.
There is a site I found, and alot of other dead links. The site that DID have it made you make an account there, then when you did that, try and open the pdf link, and they want you to PAY for it. Pay for a public released 59 year old historical document. And the quality was extremely poor photocopy. SHAMEFUL GREED!

Last edited by CivicProtection; 13th January 2011 at 06:07 PM.
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Old 13th January 2011, 07:01 PM   #9
Doz is offline Doz  United Kingdom
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Quote:
Originally Posted by CivicProtection View Post
I attempted to obtain a copy of "Magnetic Amplifiers A Rising Star in Naval Electronics"
the one from around 1951. It is apaerently the base for some later mag-amp books and full of useful information. I was looking for the full copy, not parts of it.
There is a site I found, and alot of other dead links. The site that DID have it made you make an account there, then when you did that, try and open the pdf link, and they want you to PAY for it. Pay for a public released 59 year old historical document. And the quality was extremely poor photocopy. SHAMEFUL GREED!
Unless I am very mistaken, the MV Ross Revenge (home of Radio Caroline) has a tube/mag-amp to control the steering flats... it was built in 1960
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Old 13th January 2011, 11:31 PM   #10
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Keep the comments flowing! I'm still working on new diagrams.
This ought to be right up your alley. Tubes, transistors, audio amplification and old history.
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