Also looking forward to the latest episode! Bob Heil put a photo of his mic pre-amp on E-Ham the other day to whet our appetites. I got the power supply done; it was really fun! It shows 190 volts at the output terminals.
I see someone mentioned on the U tube site that they wanted a CW rig as well. I built one yesterday afternoon and just worked K4WOP with it. Same tube I used for Bob's project. 7 or 8 parts total. donVE3LYX
Just read through this thread . . . sounds like a lot of fun ! However, I built stuff like this 50 years ago, so probably won't be doing it again. Back in those days, everyone here in the UK was on 160m (and most on AM or CW), so it was a good band for simple projects and local contacts. One of the first transmitters I built (when I was 12) was a single EF91 VFO . . . It was powered using the 250V HT and 6.3V LT tapped off my receiver (WW2 surplus CR100) - something you guys might consider, to save building a PSU. I didn't even have a tuning network on the output, just connected my 160m end fed half-wave aerial straight to the RF Choke fed anode (via a cap!) - was probably a reasonable match. Considering it was a VFO, surprising it didn't chirp when keyed. (I guess the HT voltage was pretty stable). My best contact was nearly 200 miles away! One suggestion though . . . if you guys put a Carbon Microphone (from an old telephone or a WW2 transmitter) in the cathode lead of the modulator valve, you shouldn't need an extra Mic Preamp valve. (do make sure it's insulated though !) Roger G3YRO
The audio from the set as he showed it is quite a bit above a carbon mic in the cathode lead (which will make audio if that is all U want) The supply though is a good bench supply although I did mne for higher voltage. The whole point is to get folks building and understanding I believe. Me, I did it for fun. (and it is.) The power stealing from an rx is a neat trick and I have two such CW rigs here. donVe3LYX Can't find last night episode on you tube. HELP!
Yeah, mine is done and working well. But still I would like to watch it. I listened to some on 5086 but it was after Bobs part. Tnx for the heads up. Ur right,. Goes too slow & interest will vanish. donVE3LYX
Nothing at all about the Pine Board Project this week; technical difficulties with Bob Heil connecting into the show. Hey, Don (VE3LYX), would you post a schematic of your transmitter section using the 12bh7 tube? I guess I'm not googling the right term/phrase but I can't find a schematic that looks like it would come after the mic pre-amp that uses a twin-triode. I'd like to better understand where we're going if/when Bob Heil get's there with this project.
There's a technical section for this project in the Homebrew and Kit Building section. You should post this question there.
Check this thread, post #25 https://forums.qrz.com/index.php?th...project-discussion.560412/page-3#post-4230769
There is no schematic change. A 12bh7 is wired exactly as its 12ax7 12ay7 etc cousins except it just makes more power because it was designed for a heavier service app. In octal similar is a 6sn7 can be subbed with a 6bl7 with the same result. The b tubes were used as sweep tubes in TV but pinout is the same as their cousin tubes.
