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Max Maxfield Max Maxfield
5/23/2014 02:00 PM EDT  
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Well, all I can say is that I am flabbergasted. In fact, I would go so far to say that it's rare indeed for my flabber to be quite so gasted. I was sitting here in my office slaving away over a hot keyboard when my chum Charles Fulks unexpectedly breezed in.

As you may know, Charles (he lets me call him that) leads the FPGA development group for Intuitive Research and Technology just down the road from me here in Huntsville, Ala. I shared the stage with Charles and RC Cofer at this year's EE Live! Conference and Exhibition.

You can only imagine my surprise to discover that Charles had brought me a little something. There's an old saying that goes something like "Beware of Geeks bearing gifts," but I certainly wasn't going to look this gift horse in the mouth, because this little beauty was a vacuum tube radio from the early 1940s.

Amazingly enough, I have the perfect spot for it. The photo below shows the bay outside my office. The comfy chair and ottoman in the foreground allow one to take a few minutes' break now and then. Standing against the wall is a 100-plus-year-old wooden chest, upon which rests the frame for my ongoing mosaic project -- and now my beautiful vacuum tube radio.

In case you were wondering, this bay is where I seem to end up storing the furniture my wife doesn't want me to keep in the house (LOL). On the left side of the above picture, you can see my office door. (Mine is the one with the dragon on the far wall.)

The radio is a Grundig 5088. (I need to see if I can find the circuit diagrams somewhere.) This is an AM radio with multiple ferrite rods for long-wave, medium-wave, and short-wave reception.

Charles says that, when he acquired this little rascal several years ago, he was told that it did work, though he's never tried it himself. As soon as I get a free moment, I'm going to power it up, but I will have a fire extinguisher standing by, just in case.

I would love to have this radio playing in the background in our bay. Something about the sound that comes out of a vacuum tube radio makes you want to use words like "smooth," "sensuous," "robust," and "rotund."

Of course, chances are that this little scamp won't fire up the first time. It wouldn't surprise me if we needed to replace the paper capacitors and suchlike. The problem will come with the vacuum tubes. I'm reasonably sure I will be able to pick up anything I need at the Huntsville Hamfest in August (subject of a blog post last year). The real trick is to determine which tubes need replacing.

But where can one find someone who knows how to diagnose and debug problems with vacuum tube-based systems these days? Well, you could have knocked me down with a fishwife (much more effective than feathers) when I discovered that my chum Ivan in the next bay is a diva with vacuum tubes.

Actually, this really shouldn't surprise me by now. Ivan is one of the cleverest guys I know. (Yes, I'm buttering him up; I want him to fix my radio.) When I called Ivan over to see my new acquisition, he foolishly informed me that he used to repair radios and suchlike.

Upon further questioning, I discovered that Ivan that was in an accredited trade school while in high school (he crammed standard classes and electronics classes in alternating weeks), and that this involved repairing electronic systems. While in the Air Force, he focused on maintaining and repairing electronic systems. After leaving the Air Force, to supplement his income at college, he worked at Magnavox repairing everything that came his way: CB radios, record players, AM/FM radios, TVs, laser disk players, alarm systems, audio amplifiers, PA systems, walkie-talkies -- the list goes on.

Do you ever get the impression that some things were just meant to be? I have a vacuum tube radio that needs some love, but I don't have the skill to treat it with the respect it deserves. Ivan has skill oozing out of his fingertips, but no vacuum tube radio to unleash it on. It's like a marriage made in heaven (LOL).

— Max Maxfield, Editor of All Things Fun & Interesting Circle me on Google+

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Max The Magnificent
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Re: Mysterious Object
Max The Magnificent   6/2/2014 11:22:26 AM
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@David: I'm sure even Max would struggle with 11 G&Ts for breakfast.....

Is that a dare?

Max The Magnificent
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Re: No Problem
Max The Magnificent   6/2/2014 11:21:31 AM
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@salbayeng: On a related note , be wary of metal film resistors > 100k operated at 250v or more (The Tectronix SC501 tiny scope was always having trouble with a set of 4 voltage dividers on the HT) You need to replace with "high voltage" resistors, (and preferably physically bigger resistors as this lowers the electric field)

Good tip -- thanks for sharing

David Ashton
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Re: Mysterious Object
David Ashton   5/31/2014 9:14:51 PM
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@Kfield...."did you see the pictures of him during the EE LIVE! pub crawl?"

No...you got a link??

Good to know I will have some competition if I make to to EELive 2015.....

kfield
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Re: Mysterious Object
kfield   5/31/2014 2:14:32 PM
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@DavidAshton I'm not so sure whether Max would struggle with elevenses, did you see the pictures of him during the EE LIVE! pub crawl? He was going strong late into th evening...

David Ashton
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Re: Mysterious Object
David Ashton   5/31/2014 2:14:51 AM
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@KField....  "Elevenses"....  reminds me of an Andy Capp cartoon (Andy Capp was a working-class British layabout forever shirking work, drinking beer and chatting up barmaids, and a cigarette hanging out of his mouth).  He had a long suffering wife called Flo who had cleaning jobs to bring in a bit of money.   I remember one cartoon with Flo carrying a tray of 11 beers to Andy, with the comment "Elevenses!"

I'm sure even Max would struggle with 11 G&Ts for breakfast.....

salbayeng
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Re: No Problem
salbayeng   5/31/2014 1:29:05 AM
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Yeh when I was ~8 yrs old, my schoolmates dad owneda  radio/TV repair business , we would go dumpster diving and wire up "radios" using old valves , (well we could get the filaments glowing anyway witha 6V battery !).

Built a Tesla coil (first of several) at age 15  used a 806? 810? triode (octal base with top cap anode) it used about 3 scavenged valve radio transformers to get the 1000v B+.   Made a friedd with a tech at the local radio station, he gave me some bigger valves (Used in sets of 4 as the exciters I think? they discarded the whole set when weakest valve couldn't keep up)

Not really done much with valves since.

The 110ohm observation was with a Chinese made hot air station, it had a handful of carbon composition resistors in the triac speed control. One resistor looked kind of heat stressed and was brown brown brown (and measured an erratic 63k)  , while another resistor of the same size nearby showed brown black orange and measured 10k. I swapped the suspect one with a 2W metal film 10k resistor and the speed control worked properly again.  

That sparked a recall from decades back with colleagues who had also noted propensity for drifts in carbon composition resistors that ran hot. By contrast modern metal film resistors can be cooked till the paint flakes off and show no drift.

On a related note , be wary of metal film resistors > 100k operated at 250v or more (The Tectronix SC501 tiny scope was always having trouble with a set of 4 voltage dividers on the HT) You need to replace with "high voltage" resistors, (and preferably physically bigger resistors as this lowers the electric field)

Max The Magnificent
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Re: Mysterious Object
Max The Magnificent   5/29/2014 10:06:52 AM
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@kfield: I thought you might be using it to serve elevenses!

Ah, time for tiffin :-)

Max The Magnificent
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Re: No Problem
Max The Magnificent   5/29/2014 10:05:31 AM
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@salbayeng: Tube radios don't use 110Ω resistors !

You sound like this is a topic that's pretty close to your heart?

salbayeng
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Re: No Problem
salbayeng   5/29/2014 6:08:26 AM
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@mlise: Tube circuits are pretty easy to fix, even for a digital guy. Replace all the caps. Replace all the tubes

And replace any resistors that look to have brown brown brown color bands.

(Tube radios don't use 110Ω resistors ! )

kfield
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Re: Mysterious Object
kfield   5/28/2014 9:40:45 AM
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@Max Oh, I thought you might be using it to serve elevenses!

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