5 Nov 2023 - Future Plans

A project log for Portable Radio using Vacuum tubes / Radio Valves

Create a radio receiver using vacuum tubes (aka radio valves). It will be portable, using available parts, and will look cool :)

willWill 11/05/2023 at 12:280 Comments

OK I haven't logged here for a while - some real life things got in the way, plus I had to order some audio transformers. I had a think about the general approach to this project, and I think there are 4 main steps:

  1. Power Supplies. I need low voltage supplies (LT) for the valve filaments. Depending on the type of valve these need 1.5v or 2v. Also I need high voltage supplies (HT) for the anode circuits. These can be anything from 9v to 45v for amplifiers that drive headphones, and 90v to 135v if I want to drive a loudspeaker. Some circuits also have a grid bias battery, this provides negative bias and is generally needed for output circuits that drive loudspeakers. 
  2. Audio circuits. This will be an audio amplifier that will take a 1v RMS audio signal (that's 1.4v peak, or 2.8v peak-to-peak). I think this is the same as "line out" voltage from the 3.5mm connector on laptops and PCs and possibly CD players. The audio circuit will amplify this signal and drive a small loudspeaker. Also it's possible to design a simple amplifier that drives headphones.
  3. Detector. This is the radio frequency tuned circuit and regenerative detector that uses a single valve. It feeds some of the amplified output back to the input, generating positive feedback and increased gain. This is also called reaction and was the earliest type of RF detector that could also produce some gain.
  4. Packaging. When the above steps are done I will put all the parts together and make them look nice. There are two basic types of radio receiver - one that drives headphones and the other type that drives a loudspeaker. The advantages of using headphones are simpler circuits, possibly using less valves, and not needing as much voltage in the way of HT.

I will continue to use breadboard construction for this project, as it's easier to work with and there are no dangerous high voltages. All the power will be provided by batteries.