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2020-01-18 More Zenith Royal 200 Conversion to Silicon

Continued from post 2020-01-15

I dug through my drawers and boxes of transistors and found a bunch of MPSA56 PNP general purpose on tape, and put them into the LO and mixer. I think they helped slightly – they are lower minimum fT than the 2N3906s.

I adjusted – optimized – the trimpots I had in some locations, then I unsoldered and measured the resistance. I then put in a regular resistor. The original carbon composition resistors had changed to more than 20% higher values, it wasn’t good, so replacing them has helped some, too. I still have others I should measure and replace if necessary. So far almost all of the 10% carbon composition resistors have drifted more than 10%. Some of the resistors had no tolerance band, they were 20%, but they too had drifted too much.

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2020-01-16 How To Remove Battery Corrosion

I took a battery holder that was corroded by leaking alkaline cells and I put it in a cup of vinegar. After several hours it came out clean, and I washed it off and let it dry. It looks pretty good now.

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2019-01-15 Zenith Royal 200 Conversion to Silicon

My Zenith Royal 200 conversion to silicon transistors is going slowly. Right now I’m working on getting a good sine wave out of the local oscillator (see photo). The waveform had high frequency parasitic ringing every other cycle. I put a 100 ohm resistor in series with the collector lead and it helped some. I pulled the 2N3906 out of the socket and put a ferrite bead on the collector lead and that helped a bit more. I lifted one end of the 100 ohm and put another ferrite bead on it, and it helped a bit more. At first only a single very strong station was received.  Now several more are heard. Before my modifications the sine wave had more ringing than in the photo. The photo was taken after my modifications.

I’m thinking of pulling up the end of the 100 ohm and looping the lead a few times through the ferrite bead. If that still doesn’t stop the ringing, I’m thinking about replacing the bead with an RF choke. Every time the ringing is reduced the reception gets better.  I checked to see if I had some higher inductance ferrite beads.  I found some ’73 mix’ beads and put them in place of the ’61 mix’ beads.

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2020-01-13 Slide Rule and Calculator Battery

From FB group Jan 19

Joe Haupt

In the ’80s I occasionally did work in an electrical room on campus that had a 7 foot slide rule that had been removed from the classroom. It was there for years, but the fire inspectors would make us keep the junk from accumulating in closets, so it finally got removed. 😭

I read your comment about batteries going dead in calculators. I bought a sharp LCD calculator at Sav-On Drugs back in the late 70s. The salesdroid tried to sell me 2 AA cells for it, she said the cheap Sharp batteries ‘were no good.’ I told her no. I wore that calculator out and it was still running on the same Sharp batteries years later – the current drain was so low that later they changed to button cells that last for years. 👍👍

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2020-01-11 Reinventing the Archer’s Bow – Amazing!

So why didn’t someone think of this long, long ago?  It has so many advantages.  It’s amazing! https://youtu.be/URwuU0bRMpU
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2020-01-10 Corrosion and Damage On Diode Leads

This photo is a detector diode that was broken during replacing the electrolytic capacitors.  The lead on the top was twisted, apparently putting stress on the glass package.  I replaced it with a 1N270 germanium diode.

comment from fb group Vintage Transistor Radios

Did you notice that the leads are magnetic? They stick to the speaker magnet or tools. I think they use an alloy like kovar to make the leads have the same temperature coefficient as the glass package. So the alloy has iron that rusts and corrodes much faster than copper. I’ve replaced stranded copper wire that had wicked up battery juice and was corroded inside, but it was still conducting okay. It just wouldn’t tin with solder.

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2020-01-08 Sorting Transistors Compared to Picking Fruit

I started thinking about how the makers of transistors sort the different grades of transistors as they’re manufactured. I thought that a reasonable analogy would be similar to how a farmer might sort the fruit he harvests. Here’s what I came up with.
The farmer starts with the fruit his workers have gathered.  The fruit is first cleaned then ‘culled’ to separate the rejects out of the good ones.  These are rejected because of pest damage, non-spherical growth, too green, etc.

Then the good fruit are run through a series of different sized slots that let the fruit fall into assorted sizes.  The smallest sizes are not sellable for retail price so are sent to the processing plant where they are made into canned goods.  The largest fruit may be too easily damaged during shipping so they also may be shipped to the processing plant.  The medium sized fruit are selected for produce for shipping to retail stores.  There may be other grades selected, such as color, flavor or ripeness.

My point is that transistors are like fruit in that there are various grades that are selected from the transistors made.  Some will be too high gain, some will have too low gain.  The datasheet may give ranges of gain, such as 100 to 200 for gain range E, 200 to 300 for gain range F, and 300 to 400 for gain range G.  The transistors may be sorted into the maximum voltage they can handle, or low noise performance.  The various grades may be labeled with different type numbers according to the data sheet.
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2020-01-06 Two Similar Transistor Radios

I posted this a few days ago.
https://m.facebook.com/groups/606087512820068?view=permalink&id=2638214152940717

Now I’ve replaced the capacitors in another one very similar, a DE LUXE. It’s not quite as complete and in as good a shape as the Encore.

What surprised me was that some of the electrolytic capacitors were bad (measured open) and the symptom was no sound whatsoever – not even a click when turned on – as if the speaker wasn’t connected. After replacing the capacitors, everything was normal. 🤔🤔  I could see this happening if the speaker was driven by an OTL pair with an open coupling capacitor.  But this is a regular push-pull transformer output stage. 

Thanks, Joe Haupt

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2020-01-02 Coax Cable and Crimp-On Connectors

FB comment

Years ago at work (community college) we had an IBM mainframe and the terminals were connected with coax cables. We also had thin Ethernet cabling. I had the proper connectors and thousand foot boxes of coax, and most importantly the proper stripping and crimping tools. I installed hundreds of coaxes, and I was very diligent about doing the connectors correctly. My eyesight was good, but even though every connector I installed was done correctly, there was what I thought a high percentage – maybe 10% – of shorted cables. The solution was to cut off and install a new connector. The usual reason was a tiny wire of the shield had caused the short.

The thin Ethernet cabling had the same problem. So my conclusion was that when it comes to installing crimp-on coax connectors it’s a good idea to let it be done by a factory where the pros use big bench top machines that are specially made for doing the process. The cables are better quality and the cost difference is minimal.

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2020-01-01 VA3IUL Website RF Projects

I spent too much time looking at the schematics and projects at this website.  Lots of interesting things to download.https://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/Homebrew_RF_Circuit_Design_Ideas.htm
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