Archive for the ‘Schematics’ Category:

2021-07-29 Heathkit IP-18 Power Supply Re-Cap

Last week I saw an old Heathkit IP-18 power supply on eBay for $50 OBO, free shipping. I don’t really need another PS, but I’m a Heathkit builder and a big fan. So I offered $30, thinking the seller would not take it. But a few hours later the message came that the seller had

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2021-05-11 Power Supply Protection Diodes

First off, *all* power supplies should have what this one has. A high current diode across the output jacks, cathode or banded end to positive. This is to protect the output from reverse voltage. A high current diode across the 2N3055 pass transistor, cathode or banded end towards the collector. This protects the transistor from

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2020-03-29 AM Osc + Modulation + Buffer

This is from Electronics Illustrated Projects 1968. It shows crystal sockets, but instead a RF coil may be used and its value will be about 220 microhenrys. And C1 and C2 will have to be changed to bring the frequency down to the AM band. The germanium transistors are no longer available so silicon transistors

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LED Indoor Motion Sensing Lights – Decrease On Time

I bought two of these motion sensing LED lights for my hallway. They have a rechargeable cell that is charged through a micro USB port. To see one inside watch big Clive’s YouTube video – the ebay link to buy them is in his description. The charge lasts for more than a week with frequent

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2020-02-06 Royal 500H Alignment

From FB group This Zenith Royal 500H radio has the extra 8th transistor for the RF amplifier, so it should have excellent sensitivity and be able to pick up those weak stations. Most of the problems with old radios are with the electrolytic capacitors, but the Zeniths all use the carbon composition resistors and they

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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

2018-09-02 Mims Mistakes In Audio Amplifier

From FB group Building Transistor Radios, 2018-09-02 I already see one mistake. On p.27, Audio Mixer. The R6 is only 1k. The voltage divider R5 and R6 will give a voltage less than 0.6 at Q1’s base, which means Q1 will not be forward biased enough and the circuit won’t work or else sound distorted.

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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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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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2018-03-28 Wideband RF Amp In Royal 500s

From FB group Ferrite Loopstick Antenna Experimenters Some experimenters in another group looked at schematics and saw that some radios with a RF amplifier between the loopstick and the converter used a third section on the variable capacitor to tune the RF amplifier. This is good, but it makes the variable capacitor more expensive and

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