News, Updates

4 December 2016

Website begun

7 January 2017

Audio-module squelch

23 October 2017

Sales of solid-state Audio-modules

10 March 2018

Drake SPR-4

18 December 2020

Drake SPR-4


New website

    I've finally gotten around to starting a website for my R-390A work. I've had R-390A's for about 30 years and have gotten increasingly interested in them during this time. As I approached retirement, my interest began focusing on ways to improve the R-390A.
    The current part I'm working on is the Audio-module. The motivations are: it won't drive a speaker directly, its frequency-response is limited and it generates a lot of heat.
    I've built three prototypes of a solid-state conversion that solves these problems. I'm using one and the other two I've sent to Howard Mills and Craig Anderson for evaluation. The process of installing my small PCB in the Audio-module is labor-intensive and I'm not eager to do it on a production basis. Plus, I don't know of a source of cheap, junker Audio-modules that are good candidates for the conversion. Maybe Howard or Craig will want to do conversions for other people if I supply them with PCBs.


    The latest design work on the solid-state conversion for the Audio-module has been the addition of a squelch. The original Collins squelch circuit was for tubes and could not be used. I designed a new circuit that uses the AGC line to control the squelch; a pot on my conversion PCB sets the squelch-sensitivity. Anything that makes the carrier-meter move can trip the squelch open. If a signal can't move the meter, it can't open the squelch. I added a little delay in the squelch closing time to make it comfortable for SSB signals.
    Howard and Craig are again going to be my guinea-pigs and get prototypes. I'm hopeful that they will be happy with the squelch performance and will want to start offering solid-state conversions of Audio-modules for their customers, using PC boards I supply them.

Sales of converted Audio-modules

    I've converted and sold three audio modules on eBay. I've gotten a little faster at the process but it still takes a long time, about nine hours. The eBay price reflects both the labor time and the over-$25 fee that eBay charges for every sale. I will happily sell them outside of eBay for $255 plus freight of $18 for Priority Mail shipping. If you're interested, please email me at "dash@1u2u.net."

LCD Display for Drake SPR-4

    I've been working with the SPR-4 for over two months. I have a functional frequency display and a DDS-based oscillator to replace Drake's crystal bank. This gives the SPR-4 full coverage from 200 KHz to 30 MHz with a 9-digit LCD frequency display. The prototype works great, but figuring out how to make this a saleable product is a different story. I'm adding pages to this website to document what I've done so far and what I'm doing now.

More work on Drake SPR-4

    The R-390A LCD Display is ended, because I'm out of the coax connectors. I found enough connectors for 45 kits and I've sold that many kits. The assembly time was horrible but I did it because the kit was so well accepted and it makes the R-390A competitive with current technology. But I can't find any more connectors at a reasonable price and I can't justify the time when I have the SPR-4 project to work on and three grand children to visit.
    I built a prototype of an external LCD Freq Display for the SPR-4 but it was unsatisfying. The SPR-4 really deserves internal LCD displays. So that is what I have been working on.
    I removed the dial and put the LCD display into my original SPR-4. There were several mechanical mounting problems to solve, but I'm getting there. See pics on my SPR-4 page.