Archive for the ‘Electronic Design’ Category:


June 20 Olek Kopyto What is the reason for using higher L and lower C? For parallel resonant circuits, it’s better to use high C and low L, for series resonant it’s the other way around. Higher C means the stray capacitances of the temperature sensitive components such as the transistors have less influence on

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2019-05-05 Using a 7805 For An Adjustable Regulator

from FB group Building Transistor Radios Willie Barnett When you understand how the 3 terminal regulators work, you can replace the 1N4148 and the almost impossible to get 1N34 with just a pair of resistors. The 7805 or 78L05 regulator always has a fixed voltage of 5V between the O and G pins. So you

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2019-05-02 Regen Using PN2222A Connected Backwards

from FB group Regenerative Rcvr Initiative May 3 Cyril Hodson Superregen receivers are always past the point of regenerative amplification. The AGC for a Regen should keep the regen high but prevent it from oscillating. I was thinking that a CdS photocell could be put in series with the Regen pot, and light from a

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2019-04-29 Center Tapped Voice Coil And OTL Circuit

from FB group Vintage Transistor Radios Apr 29 Robert Abend Yeah, thanks for bringing that up. Many of the GE radios have a center tapped coil in their armature speakers. I never really thought about the unusual CT voice coil. The most important reason why is that a voice coil moves and has to be

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2019-02-10 Parallel Resistors Made Easy

Something that should be memorized by every technician. This also applies to capacitors in series.

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

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2019-01-05 Substituting Chokes For A Coil In A Reflex Circuit

From FB group Building Transistor Radios 2018-01-15 Nick wants to use two 10 mH chokes close to each other in place of a coil that’s used in the typical reflex circuit. I’ll include a schematic of the circuit (from somewhere on the net). This is labeled L2. (begin my comment) Nick Bastian The coupling is

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2018-12-22 European Electronics In 1969

from FB group Building Transistor Radios 2018-12-22 Mike van Kleeff Most of the European radios sold in the US were probably brought in by GIs who came back from their military deployment in foreign countries. I was in Germany in ’69 and saw some European electronics and I was impressed by the performance. But what

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2018-12-09 Selectivity V. Sensitivity

from FB group Building Transistor Radios 2016 Dec 9 Jim Glover An ideal receiver would have a bandpass shaped like a square wave where the bandpass is flat with no attenuation and the attenuation is infinite outside of the passband. In the real world this isn’t possible but any receiver buyer with the money would

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2018-06-28 Bootstrapped For High Z Input

From FB group Building Transistor Radios For those who don’t want to or can’t use a JFET for high input impedance, you can use a regular transistor or two and bootstrapping to get a 10 Megohm high input impedance amplifier. This is from “Common Collector Amplifiers”, Electronics Now, Oct. 1993, found at For RFs,

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