Dilshan R Jayakody’s Web Log

I recently received a DIY two-tube FM receiver kit from one of my Chinese component suppliers for review. The circuit is elegantly simple, designed around a 1A2 heptode and a 2P2 pentode . The kit includes all the necessary components for the build, featuring a single-sided FR4 PCB with dimensions of 100mm × 100mm. Assembled PCB with tubes. The primary hurdle when starting this project was the complete lack of proper assembly instructions. To assist others, this article documents the exact steps I took to assemble and test the receiver. I have also reverse-engineered the schematic based on the PCB layout; a high-resolution PDF version is available for download here . Top view of the PCB. Bottom view of the PCB. The radio is designed around two main stages to handle frequency conversion and audio amplification: The 1A2 heptode - functions as a super-regenerative detector. The 2P2 pentode acts as the audio power amplifier, which receives the demodulated signal and drives the ...

This is quick (and final) post regarding our Mullard 3-3 audio amplifier project. In the last few months, we got several e-mails regarding this project and most of the people are asking for modified schematic related to this project . The schematic of our amplifier is available to download in here . Please note that this schematic is heavily based on the original Mullard 3-3 amplifier design and the main component which we replace in that original schematic is its tube base power supply unit. As a final step of this project, we construct a wooden enclosure for that amplifier and attached it to 10 inch (8Ω) full range speaker. High-resolution photographs of our amplifier are available in here . Final view of Mullard 3-3 audio power amplifier As a conclusion, this Mullard 3-3 audio power amplifier is a high-quality low power tube amplifier with minimum complexity. We really impressed with its audio quality and overall performance.

Mullard 3-3 is quite popular 3W tube amplifier introduced by Mullard Ltd in 1956. A schematic and design detail of this amplifier is available in " Mullard Circuits for Audio Amplifiers " book and in National Valve Museum article . This amplifier is based on EF86 , EL84 vacuum tubes, and EZ80 full wave rectifier tube. In this project, we decided to construct this original Mullard 3-3 Amplifier with some slight changes and commonly available electronic components. Top view of Mullard 3-3 amplifier with 6P14P and 6J8 tubes. In our prototype, we replace the EZ80 tube with 400V 5A bridge rectifier which is commonly available in many electronic spare parts shops. Also, we replace EL84 with 6P14P pentode and EF86 with a 6J8 pentode. Both of these valves can directly use with this circuit and those values are available for a lesser price than EL84, EF86 tubes.

Audio output transformers are heavily used in a vacuum tube and some (older) transistor base audio power amplifiers, but these days output transformer are quite hard to find and expensive item. For homebrew projects, the best option is to construct those transformers by ourselves and this script helps to calculate winding parameters for those transformers. This " AF output transformer calculator " script is written using Python and it works with most of the commonly available Python interpreters . The script is available to download at google drive under the terms of GNU General Public License version 3.0 . Homebrewed 25k: 4 output transformer Once supplied the input parameters this script provides a winding ratio, the number of turns required for primary and secondary winding and required copper wire gauges for both primary and secondary windings, etc. We construct several AF output transformers based on results of this script, which including transformers for M...

This is our first vacuum tube base amplifier project and this project is based on 6AS5 pentode and 6N2P dual triode. Schematic of this project is not designed by us and we got it from web. We got this schematic sometimes ago and now we can't find original site where this schematic appeared first, because of that we host copy of that schematic in here . Prototype version of 6AS5 and 6N2P guitar amplifier In original schematic, initial stage of the amplifier is based on 12AX7 high gain tube. During the construction we can't find 12AX7 in local market and because of that we replace 12AX7 with 6N2P. Both 12AX7 and 6N2P had identical characteristics and only major difference is heater configuration. After replacing 12AX7 with 6N2P, both the tubes can drive through single 6.3V filament supply. 6N2P tubes are now commonly available and we use Russian version of 6N2P (6Н2П) for our testing. We test this amplifier with 4K audio output transformer and it produces excellent ...