SA2CLC radio stuff

 A modern era tube tester? Yes, that´s right. The old radios in my basement was starting to demand a bit more than just swapping tubes. I wanted to be able to measure them. I did not really want an old tube tester, since they are felt overpriced, and building something from a kit or on your own is always rewarding.  A quick google search led me to Ronald Dekker´s excellent Utracer. The Utracer is a computer connected curve tracer, that traces the response of the device under test, on your screen. This gives you possibility to determine plate characteristics on, for example, triode connected pentodes, and there is also a quick test function, to help run through that pile of 6V6´s. uTracer3/uTracer3_pag0.html I ordered his V6 kit, and it came to my doorstep a few months after ordering, due to the fact that he was doing some tests before shipping. Why wait for V6?  Well, since I play with transmitting tubes (807´s, 6146 etc) I wanted a bit higher voltages than his V3 (true a...

2 x 813 grounded grid linear amplifier  This year marks 10 years since I built this amplifier, and it´s been in use on almost all QSO´s I´ve had since then.  When I got into amateur radio back in 2013/2014, I quite soon understood that I needed a vacuum tube amplifier. SB220´s and L4B´s were high on the wanted list, but there wasn´t anything for sale at that moment. I stumbled across a pair of 813´s and sockets, and that´s what set the wheels rolling. I begun by collecting the needed parts. High voltage transformer, variable caps, meters and such, and after that, it´s mostly a job of shaping metal and drilling holes. Most parts collected An aluminum chassis was bent using the sheet metal brake at work. Reinforcement extrusions was bolted to the underside of the chassis where the HV transformer would go. With a finished box a rough layout was determined, and the hole drilling excercise begun. Getting a feel of where to place things Lot of parts to fit. Note that pictured bandsw...

 My HP8640 died! This is me catching up on past projects. I did this back in 2022, figured someone would benefit from this information, since the 8640 is still around in great numbers at hams all over the globe. I bought a nice looking HP8640 at our local hamfest back in 2022. It was working when I got it home, but a day or two after I got it home, it started acting erratic, with RF ouput dropping out. eventually, there was no output whatsoever. Did some tests, and got to the conclusion that the cavity oscillator was not oscillating. Following various clues online, I tracked down the issue to the A3 unit (cavity), and a series resistor, which had drifted in value. By measuring the series resistance between the + feed and the A3Q1 socket and the - feed and the A3Q1 socket, I could see that the + lead seemed reasonable at 370ohms, whilst the - lead had drifted to 19Kohms, where I was expecting around 900ohms. The A3Q1 (HP21 pictured below) transistor sits under the small hex cap om t...

  2x813 G2DAF linear amplifier With the 20A in good working order, I started to think about getting a bit more useful power output. I was thinking about building a quad 807 amplifier when I remembered about an old 813 amp in the shed. I bought that amp for parts years ago, but could not find myself to part it out due to it being so well built. Upon closer inspection after I dragged it inside, I could see that it was built after G2DAF's idea  The amp is built exactly like this, except 813´s and EY81's has been used. A portion of the RF drive is rectified and doubled by the tube diodes, and fed to the screen grids of the 813´s. This saves a screen grid power supply, and also a bias supply. The voltages follow the modulation envelope, so there is no real way to determine in which class of operation the tubes are in. G2DAF amps have a reputation of being splatterboxes. My experience using this on air with the 20A has been good. I have asked people with spectrum scope receivers to ...

 Well, It's been a while since I gave this blog or Youtube any attention, but that does not mean things have been at a idle in the basement, on the contrary, quite a lot of things have gotten finished, new projects have moved in, some things have been given up on, and some have been stowed away for future endeavors :) The Central Electronics 20A It got it's recap, which went as planned. No major flaws were detected, and powering up was a breeze. I replaced the power cord with a 3 conductor cord, and found a good source here in SM for US type plugs and installed a step down transformer in the shack. (Dont want to mix things up using 115v in our 230v outlets). The 20A needs an outboard VFO. Initially I used my HP8640B (which also was repaired, should probably do a post about that as well), and that worked just fine for alignment and the occasional qso's, but a more permanent solution was needed. Alignment I tried to follow the alignment instructions in the manual, but soon ga...