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Low Voltage Vacuum Tube OTL Audio Amplifier By Usagi Electric

iMickey503

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I want to get this out of the way. The schematic.
OTL-AMP-Full.png


The Video:


I wonder if there is any real reason to even dabble into something like this because to me I don't really see much practical application since there are a multitude of wonderful tube amplifier designs and kits.

But I have yet to see a low voltage version of one. And one that works on DC. So no transformer needed.

I know that solid-state amplifiers just run circles around tube based amplification except in where you prefer to hear Distortion or the so-called tube sound. I still like them. They look like nice. Fun to build. And in my sons case? Fun to blow up when you use the wrong power supply: (12v vs 25volts)
get_hangouts_attachment_url

The Cap seems to have had a NASA Lift off event.
get_hangouts_attachment_url


My son described it as:
1645707175439.png

You know. That IEC mains powered amp looks really good right about now :cool:


After seeing this From Mr. Carlson Labs about a tube based Op Amps, I kind of like the idea of 600volts doing its thing.

So I was thinking of sending him another kit for a really nice Headphone Tube amp. Something simple enough to put together and would teach him a few things about electronics. And its always a good idea to build something and learn how it works.


Do you guys have some Intro level kits that a kid could build and put together for a headphone amp?
I really like the idea of tubes as it shows you how things work. But the kit needs to be simple so he can do it himself as I'm not able to do it with him at this time.


I would like it to look nice an be a nice display item so he takes pride in it.
Thank you bros!
 

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mhardy6647

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Pete Millett still has designs for one or two viable low voltage amps (for headphones or 'linestage' use) at his wonderful website.
In some cases, PC boards are (i.e., were) available for some of his projects.

I've built a couple of his original low voltage hybrid headphone/preamps and find them to be tons (tonnes!) of fun, FWIW.

realhifiglows.jpg


So -- I don't have 20 minutes to invest right now in that video -- what triodes is he using in the titular OTL amplifier?
 

SIY

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Pete Millett still has designs for one or two viable low voltage amps (for headphones or 'linestage' use) at his wonderful website.
In some cases, PC boards are (i.e., were) available for some of his projects.

I've built a couple of his original low voltage hybrid headphone/preamps and find them to be tons (tonnes!) of fun, FWIW.

View attachment 188834

So -- I don't have 20 minutes to invest right now in that video -- what triodes is he using in the titular OTL amplifier?
12B4. Not a great choice.
 
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iMickey503

iMickey503

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Pete Millett still has designs for one or two viable low voltage amps (for headphones or 'linestage' use) at his wonderful website.
In some cases, PC boards are (i.e., were) available for some of his projects.

I've built a couple of his original low voltage hybrid headphone/preamps and find them to be tons (tonnes!) of fun, FWIW.

View attachment 188834

So -- I don't have 20 minutes to invest right now in that video -- what triodes is he using in the titular OTL amplifier?

That looks simple enough. I don't see the normal kit there. But will check out further. THanl you!
 

mhardy6647

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Check DIYAudio, maybe?
Pete's designs are more for DIY, but there may well be boards available. That's at least halfway to a full kit! ;)
I am also sure there are other options in the form of full kits.

Note that there were a number of tubes purpose-built for low (plate) voltages. Unfortunately, the ones that were "good for hifi" have generally been scarfed up by modern hobbyists and thus aren't cheap/plentiful any more. :(
Here's a good one-stop shopping resource for info on the purpose-built "space charge" tubes from the late '50s/early '60s:
It is also possible to operate "normal tubes" in a similar mode, as, e.g., ASR's own @SIY has pointed out elsewhere.

Oh, while you're looking into all of this -- if you haven't already done so, you should acquire at least a couple different versions of the RCA "Receiving Tube Manuals"! Lots of useful information on not just the tube types, but also some basic theory, practice, example circuits, etc.
You can find some on Pete Millett's excellent resource www.tubebooks.org (look under "tube data") and even more at the truly amazing www.worldradiohistory.com site.
Specifically, see:

1645717685683.png
 

mhardy6647

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12B4. Not a great choice.
Ahh, I see. Thanks.
12B4 is a neat & fascinating tube, but, yeah, not (necessarily) for low-voltage -- although I see it does have a history of such(!?).

EDIT: I don't think 12B4s are cheap any more, either -- which would disincentivize me, at any rate. ;)
 

SIY

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Ahh, I see. Thanks.
12B4 is a neat & fascinating tube, but, yeah, not (necessarily) for low-voltage -- although I see it does have a history of such(!?).

EDIT: I don't think 12B4s are cheap any more, either -- which would disincentivize me, at any rate. ;)
Perveance is your friend. :cool:
 

mhardy6647

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Perveance is your friend. :cool:
Gotcha.
In full disclosure, that's one of those terms that still kind of flummoxes me. Sort of like snivets. At least, we don't have to worry about snivets in audio applications -- at least I don't think we do. :)

EbO_eQ5U0AAEBB1
 

SIY

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Gotcha.
In full disclosure, that's one of those terms that still kind of flummoxes me. Sort of like snivets. At least, we don't have to worry about snivets in audio applications -- at least I don't think we do. :)
Akshully... sometimes we do. Especially when we use sweep tubes (which I do on the regular).
 

mhardy6647

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Akshully... sometimes we do. Especially when we use sweep tubes (which I do on the regular).

Curses! Sniveted again!
I'd ask you how Barkhausen manifests itself at audio frequencies, but even I draw the line at going too far off-topic in any given thread!
:eek:
 

mhardy6647

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Oh, for the OP's benefit (and/or the OP's son's benefit): I'd characterize blowing up an electrolytic as a rite of passage. ;)
Usually, though, it's because one inadvertently installs a regular, polarized electrolytic backwards in the circuit. Don't ask me how I know this. :rolleyes:
 

JeffS7444

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Do you guys have some Intro level kits that a kid could build and put together for a headphone amp?
I really like the idea of tubes as it shows you how things work. But the kit needs to be simple so he can do it himself as I'm not able to do it with him at this time.
Yes, Elekit:
https://www.vkmusic.ca/TU-8100.htm
Runs off of 12V 2A brick. Haven't built this particular one but love the super tidy design which is almost completely free of wires.
 
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iMickey503

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I'll run it by my kid and ask him if this looks like something he can put together.

Are you cool with answering questions from a teenager? His 15. And will be his first real kit.

I already got him a soldering station. But his still learning the temps of stuff.

Do you have like Build of this on a Youtube video for it?
That would really help out a lot. That's kind of how kids learn how to do things these days.
I don't think I will be able to help him out with it anytime soon.

If you got a build video I could show him, I think he would say yes to it today. And I can put in an order today as well.
 

mhardy6647

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Yes, Elekit:
https://www.vkmusic.ca/TU-8100.htm
Runs off of 12V 2A brick. Haven't built this particular one but love the super tidy design which is almost completely free of wires.
That is dandy. the PCL86 is a triode (voltage amp) and pentode (power amp) in a single package, so one physical tube ("bottle") per channel.
A "spud" amp (one tuber), as... well... some of us like to call them. :)

The 6V filament version of this tube was widely used for entry level "hifi" amplifiers and kits in the 1960s; but these "odd" filament voltage variants (used in transformerless, series-filament string, "killer" radios or TVs) are still out there in warehouses! This little amp kit, of course, does include a power transformer to isolate it from the AC mains.

1645746048268.png


 
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iMickey503

iMickey503

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Yes, Elekit:
https://www.vkmusic.ca/TU-8100.htm
Runs off of 12V 2A brick. Haven't built this particular one but love the super tidy design which is almost completely free of wires.
1645745484087.png


How to order? Is it just me? Or are people who sell audio kits allergic to shopping carts?
I have to send an email to buy it? THen Paypal? Okay..

I'm sure its a great design. But I don't love my kid $275 plus shipping and then it does not seem to come with the tubes? Or the Feet or the nice knob? That/s extra?

My kids 15 and it will be his first kit. I don't think this will work out.
Its nice an all. But it seems this kits more for the advanced folks. Its nice don't get me wrong. But this one seems a bit to advanced for the beginner. And the manual is in Japanese.


Yea. A bit to high of a bar I think for his first kit. But thank you for the suggestion. I appreciate it. Maybe later on when he wants something more advanced.
 

solderdude

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and/or design? :)

I design the schematics for G1217.
Nor the PCB design (though I do give feedback on it) but am not part of G1217 nor do I make any money of it.
I do some repairs for G1217 if needed (for EU only).
Are you cool with answering questions from a teenager? His 15. And will be his first real kit.

Yes.
Do you have like Build of this on a Youtube video for it?

I don't think so. Jeremy does provide a complete kit and a construction manual.
He could check if he can do this.

This design works on a safe 24V and can drive most headphones pretty well. One can experiment with tubes and op-amps.
 

mhardy6647

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Oh, it probably is worth mentioning that the adorbs little Elekit is not a low-voltage component.
Always keep Alanis Morissette's wise counsel in mind when working with (e.g., measuring) high voltages:
One hand in my pocket...

;)

@solderdude: Thanks -- that is too cool. Those little kits look like great projects. I had no idea. :oops:
 
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iMickey503

iMickey503

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After all that.. He decided not to get a replacement. And just stuck with the stupid mini amp I sent to him by mistake. Go figure...

I have to send in his headphones back to Massdrop for repair. This model:
1647787084616.png



The Left side earcup has going bad. Glad I got the 3 year Warranty. They only lasted in Good working condition for about 3 months of use. And slowly the left side started going out.

I emailed then on Friday, and should get a response today.

Thank you for everyone who gave advice and helped out.

Please send me your Paypal so I can tip each one of you above this post.
I really appreciate your help. Thanks!
 
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