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a suitable transistor substitution for Delite amp
a suitable transistor substitution for Delite amp
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Old 18th May 2018, 12:48 PM   #1
gmurray618 is offline gmurray618  United States
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Default a suitable transistor substitution for Delite amp

Can someone please steer me towards a suitable transistor substitution for Nelson’s simplest delite amp. I’m not real concerned with the audio quality (perhaps wrongly), just that we get that magic moment when music comes pouring out of the speakers. Kind of a “hay look what you can do” project.
From Nelson’s Delite article, “This transistor is an unusual part, the Ixys IXTH20N50 depletion mode Mosfet. I got them from Digikey for about 6 bucks (and I had to buy 60).”
When I priced them they at mouser.com they were $21 and I had to get 30 and they were out of stock.
And so, …
I’m hoping to find something for a good bit less that I can use in my classroom to teach about electricity in an ‘introduction to engineering’ class that I’m putting together for next year. I pretty much have free rein to incorporate whatever projects I want to, but not such an open ended budget, so some of this may fall on me. If I/you can find something cheap enough I’ll get a bunch for the whole class and they can do little mods and see what happens etc.
http://www.firstwatt.com/pdf/art_delite.pdf

I don’t have a lot of experience (hence my rather basic question). I have built the F5 (I’ve meant to thank you for your help 6L6. You Rock!)

Thanks all in advance
George
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Old 19th May 2018, 04:11 AM   #2
aspringv is offline aspringv  Australia
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a suitable transistor substitution for Delite amp
Why not make the zen with a light bulb? Then you've a mountain of parts that are cheap and available to choose from.
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Old 19th May 2018, 04:15 AM   #3
PRR is offline PRR  United States
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Quote:
Originally Posted by gmurray618 View Post
...“This transistor is an unusual part, the Ixys IXTH20N50 depletion mode Mosfet....”
http://www.firstwatt.com/pdf/art_delite.pdf
...use in my classroom to teach about electricity in an ‘introduction to engineering’ class
Note that this amp is suggested for 60V-100V. This is awful close to high voltage for a non-college classroom. (OK, we played with a 3KV supply in my high school....)

{sigh} Did you even look for the Fig 7 device, IXTH6N50D2? Mouser has 120 to sell one by one, six bucks.

{what I was gonna say} The description may be more helpful than the actual part #. Putting "depletion mode Mosfet" in Google turns up hits. One at Mouser, where you were. They come very small and very large. Selecting Pd 20W-100W gets all sub-Amp devices. Selecting Id >1A gives some oddballs, but IXTH6N50D2 and IXTH10N100D2 are promising. IXTH10N100D2 will sit at 1.5A with -2V bias, which is the right ballpark, except return gate to zero instead of to source. SADLY this is the 12-buck part, but they do have 120 and will sell you just one.
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Old 19th May 2018, 05:35 PM   #4
gmurray618 is offline gmurray618  United States
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PDR $6 is reasonable. Thanks for the pointers on finding replacements. I really want to keep this as simple as possible. Which leads me to thank aspringv. I had forgotten about the Zen amps. Read about them five or six years ago, but without the intention of building one. But now I think that’s what I want. Single transistor, a simple circuit without the need of a PCB (more $). Perhaps one or two of my budding electrical engineering students will get hooked and continue on. I teach in a poor district so seeing that light of excitement and understanding is just wonderful.
Of course I love it too.
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Old 19th May 2018, 08:45 PM   #5
gmurray618 is offline gmurray618  United States
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Just to make it easy: Zen amp 404 Not Found

Looking at fig. 5, am I correct that C1, 2 and 3 are electrolytic caps and C4, 5 and 6 are film caps?

Sticking with the IRFP240 transistor, it’s only about $2 at mouser

I don’t see much guidance on a heat sink so I’ll have to dive into that next I think.
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Old 19th May 2018, 10:20 PM   #6
Nelson Pass is offline Nelson Pass  United States
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a suitable transistor substitution for Delite amp
Quote:
Originally Posted by gmurray618 View Post
I teach in a poor district so seeing that light of excitement and understanding is just wonderful.
Yes, and it recalls an early Burning Amp Festival when my talk consisted
of assembling a DeeLite from scratch, clip leads and all, culminating in the
moment when the lights came on and the music played.

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Old 19th May 2018, 10:44 PM   #7
aspringv is offline aspringv  Australia
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a suitable transistor substitution for Delite amp
The heatsinks are the beefy bits, and I'd imagine you're going to have an interesting time with the eventual case and power supply too. Particularly if said students are going to take these home eventually?

Anyway. The most budget heatsink I've used was a piece of ally extrusion used for solar panel framing cut into pieces (the 'fins') and bolted to a ally plate. The extrusion pieces were free (offcuts) and the plate was a few bucks.
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Old 30th May 2018, 06:35 PM   #8
gmurray618 is offline gmurray618  United States
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So far I've found parts for 15 Zen amps for about $100 - $130 each. I think that's pretty awesome!

Zen Variations 1 | Pass DIY

I do have a heat sink question.
I have a heat sink that was used for an old desk top computer (Intel® Celeron Dual-Core 3300/2.50GHz). It has a copper base and four heat pips that pass through 32 plates. The plates are 3.5in x 2.5in (9cm x 6.5cm).

It looks like the one towards the top of the page. Understanding CPU Heatsinks: Picking the Best CPU Cooler | GamersNexus - Gaming PC Builds & Hardware Benchmarks
The anatomy of a heatsink.


I have the fans if necessary (I was thinking they might be large enough with the fans and using a voltage source closer to 40V than 80V).

I was also wondering if a 20V laptop charger (with some smoothing of ripples) would work. The cost up above does not have a power source yet.

Last edited by gmurray618; 30th May 2018 at 06:37 PM. Reason: got rid of bad link.
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Old 30th May 2018, 10:24 PM   #9
woody is offline woody
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Have you considered just building the ACA they use a laptop power supply and don't need any extra filtering .
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Old 31st May 2018, 12:06 AM   #10
gmurray618 is offline gmurray618  United States
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I thought about the ACA but like the simplicity of the Zen. My students have (like almost all high school kids) no experience with resistors capacitors or circuits in general forget ever having soldered. The Zen has a single transistor which I think is an easier concept than the push pull of the ACA - and we can play with the circuit more easily and safely (I’ll have a few extra of parts).
Also the ACA kit is a kit. Just not as cool as a buch of parts and a diagram and point to point soldering. And it’s about twice as much money. Most of that is the case which is very nice, but I’m going for student creativity here. The only ground rule is to have (and understand) good grounding.
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