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Author Topic: Heathkit "Basic Radio" Course  (Read 18805 times)
KB1WSY
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« on: August 06, 2012, 07:26:16 PM »

Greetings,

Heathkit had a "Basic Radio" course based entirely on tube technology in the late '50s and through the mid '60s. It was a two-part set. The EK2-A starting with very basic radio concepts and culminating with a Regen set. Then, EK2-B culminating with a Superhet covering BC and SW (including ham 80m and 40m) with a BFO. There's also the AK-8 but that's just a vinyl-covered wooden cabinet to "embellish" your finished radio.

Until recently I thought this whole thing was surely a silly "toy" but then I bought (on Amazon.com) used paper copies of the manuals. You can also find these manuals online BTW although I am not sure what the legal situation is, so I played it safe.

Anyway, I was just blown away by the manuals. They are not the Heathkit manuals I remember: not only are the construction details very, very well done (as with all Heath manuals ) but there is heavy emphasis on teaching you the theory: all of the minutiae of tube electronics, the role of each element, biasing, tube capacitance, bypassing, just wonderful. The manuals are each about 100 pages. Bravo! I don't remember seeing these particular "educational" projects in the Heathkit catalogues of my youth but I must be slightly too young (born in 1957).

Fast forward to 2012. The problem is the current fetishism with "unbuilt Heathkit." On eBay the EK2A/B and AK-8 combo "unbuilt" fetches at least $300 -- that's what I've seen in an auction a few weeks ago and also in one tonight that has already hit $297 (including shipping) with 19 bidders and the auction isn't even over yet. That's daft. There would be no point actually building the kit because it would lose all of its value the moment you made the first solder joint!!!! In fact, I suspect that some of these kits are bought by collectors who wouldn't consider ever actually building the thing.

So here's what I've done:
--Obtained used copies of the manuals.
--Picked up a cheap, run-down, already-built EK2-B superhet complete with its sad looking vinyl covered wood cabinet and overall "orphan abandoned in the garage for 50 years" sheen.
--I am disassembling the radio and salvaging the chassis and the key "relatively valuable" components in a 21st Century context (the variable cap, the dinky dial, the coils, the power transformer, the tubes).
--There are components missing (because building the EK2-B involved removing EK-2A components from the chassis and the original builder tossed those years ago) but it looks like I already have most of those in the junkbox.
--Plus many of the original components, such as the caps, will be replaced with modern or NOS equivalents from the junkbox.

Total cost so far, about $60 including the notional cost of the stuff that came from the junkbox. Not cheap, but not ridiculous either.

Yeah, tube-radio-building nirvanah! The manuals have been bedtime reading for a couple of days and there is extensive assembly/disassembly with the soldering iron, interweaved with solid theory, much of which I supposedly "already know" but have never been taught "interactively."

Bravo Heathkit! Until now I'd never quite realized the educational impact they had -- as a teenager those were presumably the least interesting kits for me! I just wanted to get on the air!

Of course, what I'll end up with after many hours of assembly/diasassembly is a pathetically crappy single-conversion super, a terrible radio in every way. But it is amazing how Heath walks you through how it actually *works*!

I'll update this thread when I get going on the "Basic Radio" course. Or, if enough of you shoot me first, I won't!

73 de Martin, KB1WSY
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KA4POL
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« Reply #1 on: August 06, 2012, 09:59:57 PM »

Very interesting writeup. Are you aware of the Heathkit Yahoo group which can be extremely helpful?
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KB1WSY
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« Reply #2 on: August 07, 2012, 03:52:13 AM »

That ongoing auction last night that I mentioned in my previous post? The complete, unbuilt EK2A/B+AK8 ended up selling for $615.99. There were 25 bids; numerous enough that perhaps one of the bidders is reading this.

See: http://tinyurl.com/8k8s8gp.

Thanks for the tip about the Yahoo group -- I'll check it out if I hit a problem with unobtainium although so far it looks like I have all the needed components for all the "experiments." Actually this education kit series is the only Heathkit I'm currently interested in, since my overriding interest is "true" homebrewing. I made an exception for the educational stuff because the aim in that case isn't really to build a cool radio, but to learn stuff about radio and tube electronics, and I love the way it's done.

I built a half-dozen "mainstream" Heathkits as a teenager in 1969-1972, culminating in an HR-10B receiver, but I cannot say that the process taught me much about radio electronics.

73 de Martin, KB1WSY
« Last Edit: August 07, 2012, 04:47:43 AM by KB1WSY » Logged
K5MF
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« Reply #3 on: August 07, 2012, 08:05:37 AM »

This sounds like a great project.  I remember when the IT industry switched from field troubleshooting to modular replacement, IMO, technician skill sets suffered.  There is no better way to figure out what is wrong than to know how it is suppose to work in the first place.  Have fun with your project.
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AC5UP
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« Reply #4 on: August 07, 2012, 08:18:54 AM »

Years ago you'd see an All-American Five 'trainer' in electronics schools that was built on a Masonite board approximately 3' x 6' and intended as a functional wiring diagram / schematic. Plug it in, turn it on, point at it with a stick and explain to the class how RF goes in one end and audio comes out the other. Everyone learns in their own way, but most of us are visual and seeing the actual hardware can give a student something to wrap their mind around.

Best example I found on the web is a modern equivalent that looks like:  http://www.allspectrum.com/store/images/amfm108k.GIF

Transistorized, minimal labeling by section, the FM tuner is on the upper half with the AM tuner and audio on the lower half. $32.00 + shipping can put an unassembled kit on your doorstep: http://www.allspectrum.com/store/amfm-radio-kit-and-training-course-14-transistor-diode-version-without-ic-p-944.html

This isn't the perfect match for someone wanting to learn how a tube radio operates, but it can de-mystify the fundamentals of Superheterodyne design. Once someone 'gets' the basic idea well enough to visualize signal flow the rest is detail work. You'll know when you're there on the day when you can read a chassis or schizmatic like a map and find the local oscillator, IF strip, detector, etc. by proximity to component landmarks... Translation: The antenna circuit and local oscillator are always connected to the tuning condenser, the nearest tube is likely the converter / oscillator which in turn drives the 1st IF transformer. If someone really wanted the tube experience, they could score a junker AA5, disassemble same and re-assemble the obsolete parts like the transformers and front end pieces onto a breadboard to make their own "Visible Radio". I'd use all new resistors & caps for the sake of convenience, then label everything by function.

If that doesn't help you figure out how the sections work together, remember that stamp collecting and bird watching are excellent hobbies..............  Tongue

BTW: There are a ton of college and trade school level web sites that teach how & why various circuits work the way they do. If a person took the time to learn the characteristics and application of common parts it wouldn't hurt a bit.
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KB1WSY
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« Reply #5 on: August 07, 2012, 09:06:36 AM »

You'll know when you're there on the day when you can read a chassis or schizmatic like a map and find the local oscillator, IF strip, detector, etc. by proximity to component landmarks... Translation: The antenna circuit and local oscillator are always connected to the tuning condenser, the nearest tube is likely the converter / oscillator which in turn drives the 1st IF transformer.

I'm already at that level and in fact was at that level as a teenager. The challenge for me has been to move to the next level of detail, which is being able to look at a schematic and identify:

(a) What "type" of oscillator or amplifier it is (Hartley or Colpitts? Class A or Class B?) and what are the salient characteristics of said circuit? I never got that stuff internalized, so I'm constantly going back to the textbooks and re-reading stuff. Even when I stick my nose in the book, it doesn't seem to "stick" such that I would remember it tomorrow or next week.

(b) The function of every component. It's easy to identify a main tuning circuit, an IF strip, a detector, a grid bias resistor or a pi output circuit. I can usually look at, for instance, the schematic of a double-conversion superhet and accurately turn it into a block diagram. However It's much harder to grasp what *each* "non-landmark" component is doing.

(c) My gut feeling is that this only comes with hands-on building, so that you are constantly going back and forth between the abstract and the concrete. In that respect, the Heathkit course is a brilliant first start since you literally switch between theory and construction from one paragraph to the next.

Until I achieve such "fluency" all of my homebrew projects will, of necessity, simply be slight re-workings of projects designed by other people. This is "homebrew" only in the sense of saying, "I built it myself and I understand how it works." Wouldn't it be cool to be able to add, "I designed it myself, based on my knowledge of the standard elements of basic radio theory, and when it didn't work the first time, I applied my knowledge to fix the problem and thereby learned a bit more theory in the process."

73 de Martin, KB1WSY
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KB1WSY
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« Reply #6 on: August 08, 2012, 01:59:38 PM »

I received the EK2-B today and plugged it in. It works! Whoever completed this radio course 50 years ago did it right! Here are some photos prior to disassembly:

http://tinyurl.com/8zo3qdl

http://tinyurl.com/dxcylao

http://tinyurl.com/cp9uxhk

I'm really looking forward to this!!!

73 de Martin, KB1WSY
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KB1WSY
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« Reply #7 on: August 08, 2012, 03:49:27 PM »

So, I hooked up the EK2-B radio (before disassembly) and tuned it to one of the "vintage" AM stations playing hits from the 1960s or even earlier.

Two observations:

(1) Despite my fundamental skepticism about "the tube sound" these vintage songs sound more authentic and "more full" on a vintage radio despite the tiny 3" speaker. I'm a musician, sort of, and suspect that this is only the result of some pleasant (but reality-altering) harmonic distortion.

(2) The XYL *loves* how it renders her favorite AM baseball station (we are in RedSox land) therefore this radio is hers once I have finished tearing it apart and rebuilding it, with all of the prescribed Heathkit "experiments" along the way (it begins with a crystal radio and ends with a 5-tube superhet).

I'm hoping that (2) will help maintain domestic peace.

73 de Martin, KB1WSY


« Last Edit: August 08, 2012, 04:36:28 PM by KB1WSY » Logged
AC5UP
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« Reply #8 on: August 08, 2012, 04:36:11 PM »

Vinnie will be joining this thread in      3........        2........         1.........

Tube radios often do sound better than their modern counterparts but the difference isn't entirely because of the tubes. Modern sets typically use ceramic resonators instead of slightly more costly IF transformers and the problem with them is twofold: They're non-adjustable so if you get a pair that are off in frequency with one a little high and the other a little low the passband will be clipped and there's no easy fix. I've also had radios that gave me a strong vibe the filters weren't exactly symmetrical. That's hard to quantify without a service monitor, but I can tell you an old-school IF transformer can be ballparked by ear (not recommended, but we've all done it) and with a sweep generator stagger tuned for best fidelity.  A ceramic filter is what it is.

BTW:   N4NYY can vouch for the joys of listening to a baseball game on a tube radio, I can tell you that Rush Limbaugh sounds best on a German radio, and rumor has it Alex Jones sounds best on an ARC-5 in a concrete bunker........   Grin
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G3RZP
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« Reply #9 on: August 09, 2012, 02:33:15 AM »

'5UP,

I think another thing about the ceramic filters is the group delay. Many years back when I was doing an Application Note at Plessey Semiconductors, I found that using a ceramic filter at the back end of 455 IF strip produced noise with a definite pitch to it - similar to the effect of varying the BFO on a classical  tube receiver. This was not present with a quite high Q  tuned circuit, or even a higher Q IF transformer that I made - pot cores, bunched conductors, unloaded Q of 150. I put this down to the group delay variation in the ceramic filter leading to components of the noise at one frequency being delayed enough for it to no longer have any correlation with itself and thus effectively producing a beat frequency in the AM detector.

Although we are frequently told that the ear is insensitive to phase difference, I am not so sure that really applies when we are talking of a multi frequency signal such as voice or more particularly, music.
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KB1WSY
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« Reply #10 on: August 11, 2012, 04:49:56 PM »

I've been "doing the inventory" before embarking on Heathkit's "Basic Radio" tube electronics course from more than 50 years ago. The model numbers are EK2-A, EK-2B and AK-8. To save money, I found a $30 beat-up, already assembled "Basic Radio" which I am disassembling -- the "unbuilt" versions are selling for more than $600 nowadays which is a lot more than I can stomach. I also obtained the original manuals. In the radio that I have (picture here: http://tinyurl.com/8zo3qdl) the only missing components are those that were used *only* in the "Part One" EK2-A "experiments" and were then removed from the chassis when it was "upgraded" to the EK2-B which is a very basic superhet with BC and SW bands plus a VFO. The radio, to put it charitably, is mediocre but the educational content of the course is extremely impressive.

So what components am I missing in order to complete the EK2-A "experiments? A few things that are really easy to replace (a crystal radio earphone, a germanium diode, a few resistors). There's only one thing that's a bit harder and that's the "regenerative detector coil" which has a primary, a secondary and a tickler. I've joined the Heathkit Yahoo! group just in case someone has one of those coils, but otherwise I will simply rewind it myself. Here's Heathkit's own description of the coil:

http://tinyurl.com/cz8hhu3

And here's an under-chassis photo that shows the radio's other coils, which use the same coil-form-factor as the coil I am trying to replicate:

http://tinyurl.com/cp9uxhk

I'm forging ahead but any advice would be welcome. The primary of my "mystery coil" is a pi-wound, universal primary coil at the top of the form, and I can probably adapt/butcher an existing Miller or Merit coil to get that and then wind my own secondary and tickler. This "regenerative detector coil" is used in a really basic, one-tube regen receiver that forms part of the Heathkit radio course. Although I could probably just skip that "experiment" altogether, I am rather enjoying the challenge of trying to complete the "experiment."

I have a Morris coil winder but have never used it.

The other possibility is that one of you has this coil (Heathkit part # 40-303) at the bottom of a drawer somewhere ... wouldn't that be bizarre? Can I borrow it? (I can always send it back to you once I get to Part 2 of the course!)

73 de Martin, KB1WSY
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KB1WSY
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« Reply #11 on: August 14, 2012, 06:15:37 AM »

Here's another, even more detailed description of the coil I am looking for, including where to find it on the EK-2A/EK-2B chassis if you happen to have one lying around for the past 50 years:

http://tinyurl.com/8w7z5dm

73 de Martin, KB1WSY
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