2019-02-01 Raytheon 1N128 Germanium Diodes

Link left on FB group Building Transistor Radios

Someone in the group mentioned a source of crystal radio parts, Small Bear Electronics and linked to their website. I found that they had some germanium diodes, Raytheon 1N128, and they showed the reel of them, so I thought my chances of getting factory parts would be better if the diodes were still in some form of packaging. So I ordered a dozen and a half at $0.00 apiece. The next week I received a bunch of 1N128 diodes from Small Bear, but all of them were loose and marked with the letter T. I’ve seen that before, it was the symbol for Transitron, not Raytheon. I emailed the company and asked to exchange them for Raytheon diodes, or else I asked for a refund if Raytheon diodes were not available. The guy apologized and said he would send them out. A week later I received the package with the real Raytheon 1N128 diodes, which still were on tape.

Today I took the time to check some of the diodes out. I wired a AAA cell, a 100k resistor and the diodes in series and connected a DMM across the 100k resistor. I connected the diodes in reverse, and I expected to read a small leakage current through the germanium diodes. I connected one of the Raytheon 1N128 diodes and found that it had about 25 microamps leakage. That seemed okay. I connected one of the Transitron 1N128 diodes and I saw no voltage across the 100k like the diode was open. I reversed the diode and it gave the same open reading of zero. I could get the DMM to give a fraction of a microamp reading by squeezing both leads of the diode with my fingers, so I knew there was nothing wrong with the test circuit. I used a sharpie marker to blacken the diode and then I tested another diode. It was also open, an insulator, not a semiconductor. I continued testing and found only a few that were somewhat semiconducting. One seemed to be mismarked, it was backwards. Another was about as semiconducting one way as the other, but most of the diodes were just insulators. I could understand it if I got one bad one out of the whole bunch, but in this case only one was somewhat good, and all the rest were bad. These Transitron 1N128 germanium diodes were floor sweepings or factory rejects – they were all useless. Needless to say I will not be making any more purchases from this company.


2019-01-27 Replacing Corroded Battery Contacts

From FB group Building Transistor Radios 2018-01-27

Many of the radios I’ve acquired were so corroded that I had to replace metal parts. I used tin can lids to make replacement battery holder contacts. The steel is springy enough to hold cells in place. Scissors can cut the steel, and it can be drilled and worked by hand.


2019-01-20 Lower Price Radios Competition

from FB group Vintage Transistor Radios 2019-01-21

Mike van Kleeff
There was a lot of pressure on domestic radios from cheaper Japanese and other imported radios. So Zenith and others had to cut costs and sell in the low price ranges. I would say that all radios, wherever they were made, were less substantial than before due to lower prices. That doesn’t mean that the performance was compromised, at least not a lot. You can’t get as good a sound out of a smaller speaker. 😎😎


2019-01-18 Tilt Wing Aircraft In The Future

From FB public comment

The military had a lot of problems with their tilt wing aircraft similar to the one in the picture. The solutions often involved a lot of frequent maintenance and repair. It may not be possible to fly such aircraft profitably in a commercial airline.

Another thing that’s going to change the air transport system is the high speed rail lines. The rail may replace the shorter air routes.

Only time will tell how all this turns out. We have yet to see any of the stuff that they predicted decades ago, like in the Jetsons cartoons. 😏😏


2019-01-17 Power Outlets Made From Electric Outlets

From FB comment to Bill Sherman’s post

Bill Sherman

The cable jacket may be too big diameter to fit into the clamp. But you might consider the special 20 amp plug, the one they put on the power strips that are used in the server racks. I forget what they’re called, but we specified those when the electrical contractors installed the outlets under the raised floors.

Nasty fire inspectors saw the bespoke outlets like yours that we were using under the office desks and they wrote us up because every ‘power strip’ had to have a 15 amp breaker and an on/off switch. So I got a bunch of them and I used them for decades in our *temporary* computer setups during peak periods, which then got taken down later. Those were a fire inspectors’ nightmare! 😱😂😂😂 They work great, and ours didn’t have a switch, which sometimes got accidently turned off which shut down a whole row of PCs. 😬😬


2019-01-15 2nd FM Microphone Kit Assembled

I ordered some other FM Microphone kits, and assembled one last week. This is a better one, labeled EEQKIT RF-02FM VER170525. It has three transistors, one of which is a microphone preamp and it should perform much better. The kit also has a jack that will allow you to plug in a stereo signal from a CD or other audio source and broadcast a mono signal. The link and schematic are below.

I assembled it with no problems, the parts were labeled on the PC board. The “7 turn” is the coil with the plastic and the tuning slug. One thing I like is they used a 10k for the LED current limiting resistor so the LED draws only a fraction of a milliamp, which saves the battery. The red LED is still bright enough.

I powered it with a 6 volt Ni-MH battery pack, the board is marked DC 3 – 6V. I monitored its output with an FM radio. I tried to find my ‘station’ on the FM band but I didn’t hear anything. I got my Gooit frequency counter and put it next to the antenna and it was saying 320 MHz! That’s way too high! So I found a tiny screwdriver and gently and slowly turned the black tuning slug in until I got the frequency down to the bottom of the FM band around 90 MHz.

I tuned in the radio and blew into the microphone but the audio was very weak. That should not happen because the kit has a microphone preamp. So I measured the collector of Q1 and it was less than 0.8 volts. It should be about half the supply voltage or about 3 volts. I checked the 9014 datasheet and saw that it is a high gain preamplifier transistor. The schematic shows that its base is biased by R4, which was 100k. Most low level preamps use a resistor much higher, from 470k to 1 megohm or more. So I replaced the 100k with a 470k and the collector measured about 1.8 volts, which is much closer to half the supply voltage. I powered it up and the microphone was much more sensitive, I don’t have to yell in it to be heard on the radio. So the conclusion is that the kit should have a much higher value for R4, 470k should be okay.

A link to the kit instructions (.PDF)


2019-01-11 The 1N60P “Germanium” Diode Issue

From FB group

Markku Vuorensivu
I bought some 1N60P “germanium” diodes and I found they are not germanium, they are Schottky silicon diodes. They do not work like germanium diodes in circuits that depend on the leakage that germanium diodes have. The Schottky or germanium diodes can be checked for reverse leakage and germanium will have less than 1 hundredth of the microamps of leakage that a germanium diode has. I suggest that anyone who recommends these also reminds readers about this issue.

Here is a video on YouTube about how to tell one from the other.


2019-01-10 The Ninth Anniversary Of The Philips LED Candelabra Lamp

On Jan 11, 2010 I connected a Philips candelabra lamp to the AC line and turned it on, and for the last nine years it has been running continually, except for a few days time when the power was out, which might add up to a few days, probably less than a week. I did this test because there were several companies giving LED lights a bad name by selling lights that would go dim after less than a thousand hours. I was sure that Philips was not one of those companies so I used a Philips light for the test. Philips LED lights, and any LED lights were expensive in 2010. The prices for 60 watt equivalent LED lights were $20 or more. The prices have come down dramatically since then, and the LED lights have contributed substantially to the reduction of electricity usage.

So 24 hours times 365 times 9 years gives 78,840 hours, and to cover the days of power outages I’ll round it down to 78,600 hours. Most LED lights say they will last 25 thousand hours but some LED makers said the LEDs themselves should last for 100 thousand hours. My LED light is still bright after 3 times its 25,000 hour lifetime. The light has gone more than 3/4 of the way to the hundred thousand hour mark.

In 2010 I didn’t have a luxmeter to measure the light’s output, so I tried to measure it with an old GE light meter for photography. But it didn’t give an accurate reading and it doesn’t work anymore. I can only give a guesstimate by eyeball. There has been some drop in the light output but it still looks bright.


2019-01-09 Bootstrap Principle In Audio Amps

FB group Building transistor radios 2018-01-09

Willie Barnett
That is one deficiency of your circuit: the output transistors do not have the ‘bootstrapped’ bias resistor.

I’ll explain why it’s needed. In your circuit, the signal turns the driver transistor as close to off as possible. The current through the base bias resistor causes the top output transistor to turn on. But the transistor’s base and emitter voltages go higher, and as those voltages approach the + supply V, the base bias resistor has less and less voltage, so it can’t supply the needed current. The transistor becomes current starved. So in your circuit the upper output transistor can’t drive the speaker close to the + supply V.

To solve this problem the spkr is connected to positive and as the voltage across the spkr goes positive it adds to the + supply V. The base bias resistor gets its current from the capacitor end of the spkr, and the bias resistor always has voltage across it, so there is no problem with current starvation.

Another way to solve this problem is to split the base bias resistor and connect the split point through a capacitor to the output. In this case the spkr can remain connected to ground.

The 4.7k can be lowered or made zero. But the circuit should have a small capacitor from collector to base of the driver transistor to prevent it from oscillating. But then maybe you might want it to oscillate, so it can drive a 50 ohm antenna at a ham frequency??


2019-01-08 99 Cent Wireless Microphone Kit Assembly

2018-01-08 also FB group Building Transistor Radios

Before the Xmas holidays I ordered a few of these at 99 cents apiece, and they gave a delivery date of late Jan to early Feb, so I was pleasantly surprised to get them early.

There are many of these single transistor microphones around, either as schematics or as kits. They have low audio sensitivity because the microphone puts out only millivolts and that’s not enough to fully modulate the RF oscillator. Blowing in the microphone is easily heard, but for your voice to be heard you have to talk loudly very close to the microphone.

This kit comes with a coin cell holder that will take a CR2032 3 volt lithium cell – it’s very compact, but the lifetime is not very long. I didn’t have a coin cell so I soldered a two AAA cell holder to the kit to try it out. All of the resistors are 1 percent, which is better, but the color bands are harder to read than 5% resistors. All of the capacitors are very low cost ceramic disks, and do not give the circuit good frequency stability.

This kit came with the hole in the PC board for a short antenna, but there was no wire for it, they assume you have a short piece of wire available – short meaning a foot or 300 mm. But when the antenna is used the frequency will change when the antenna is brought near other objects. Without the antenna the signal can be picked up a few tens of meters.

The coil comes already made, and measured 100 nanohenrys, which is typical for the low end of the FM band. The turns of the coil can be spread to increase the frequency, because the 30 pF tuning capacitor is fixed and can’t change the frequency. But this 30 pF value is on the very high end of the typical values found for the low end of the FM broadcast band. Also C5, the capacitor connected across the emitter and collector, is 10 pF, which is double the values typically used. In addition there is a capacitor C6 across the emitter resistor is usually not used, but in this case is 30 pF. All this adds up to more capacitance for this circuit and a lower frequency.

So after assembling the circuit I powered it up and measured the frequency with my Gooit frequency counter, and I got 78 MHz, more than 10 MHz too low. So I removed the 10 pF C5 and put a 5.6 pF in its place. I checked the frequency and it was still below 80 MHz. So I removed the 30 pF C6 and put the 10 pF in its place. The frequency then measured 81 MHz, still way too low. So I had to lower the 30 pF tuning capacitor C4 and put a 20 pF capacitor in its place. Now I measured 91 MHz, just about right. I can put a 0.5 to 5 pF variable capacitor across this 20 pF and move the frequency down to the 88 to 90 MHz part of the band.

The circuit needs another transistor to amplify the microphone so the listener can hear what is being said in the room. I will have to see if I can add a transistor and a few parts to make it more sensitive. As it is now it’s more of a kid’s toy, not really useful for listening.

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