Archive for the ‘Radio Frequency’ Category:

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

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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

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2020-01-06 Two Similar Transistor Radios

I posted this a few days ago. 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

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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.

2018-09-28 LM386 Used As Modulator of Final RF Output

From FB group Building Transistor Radios 2018-09-28 I see nothing wrong with using the ‘386 to directly drive the power output stage. It’s cheaper than a transformer. But I was thinking about how the current was flowing in the ‘386’s output transistors. Normally an electrolytic capacitor blocks any DC from flowing out of pin 5.

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2018-09-11 Vectronics Aircraft Radio Kit

I got the Vectronics VEC-131K aircraft band radio kit in the mail yesterday and warmed up the soldering iron to assemble it. It came at a decent price, so some of my complaints seem to be cost cutting measures. It comes with a decent assembly instruction manual, but some of the pages including the schematic

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2018-09-07 Q of an Inductor

from FB group Building Transistor Radios, 2018-09-07 Tom Miller Say a capacitor or inductor has a Q of 100. The losses are about 1/100 of the energy in the component. In a tuned circuit the capacitor Q is usually much higher than this – it has lower losses, so the more important is the Q

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2018-08-30 Using Radio Signal To Power A Receiver

From FB group Building Transistor Radios 2018-09-01 There are too many ‘gotchas.’ You have to put up a large sized antenna to gather enough power to run the circuit. That means you cannot use this in a city where the properties are too small, due to lack of space. You go to the country where

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2018-07-25 How Stable Are Regen Reflex Radios?

From the FB group Building Transistor Radios Regenerative / reflex designs are not as stable as superheterodyne radios. One problem is the design depends on factors that are not predictable such as gain and feedback, which are not linear. The regenerative reflex depends on the circuit being on the verge of oscillation, which is not

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2018-07-24 “Boy’s Radio” Reflex Schematic

From FB group Building Transistor Radios Willie Barnett I see from the schematic that this is a reflex regen. They did something else that is very seldom seen, the volume control acts not as a normal variable voltage divider, but instead as a variable shunt load across the secondary of the driver transformer. This is

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