Great series, just in time. I saved mine built from the 1962 Handbook since constructing it in Jr. High shop class,1967, as WN6CAB. This time, i stripped it down and used as many original parts as possible. A definite re-learning experience! I hope to put it on 40 soon. Again, thanks for posting. 73s de WA6CAB
I built several 'power-oscillator' transmitters and every one was a pain and more of a lab experiment depending on crystal and antenna. The best one was a 6146 for stability and output power but you always give up most of what power you could get out of the tube you're using, if it was just a PA. So, I quickly moved on to using a separate Xtal-oscillator (6C5, 6F6, 6V6, 6AG7, 6J5, 6C4, 6CL6 even 5763) and that made my life soooo-much easier that I never messed with power-oscillators again. [edit: also stole a 6AU6 oscillator design from a 51J that was very stable.] When you use a separate tube and even a buffer; (in fact a 6U8 is an excellent example) to feed a power tube, you can really get a MUCH-BETTER bang out your 6DQ6 or 6LQ6 or whatever sweep tube. So, whIle nostalgic and cute, I never recommend someone build, as I'm sure a lot of novices had difficulty. The best topology I found and liked (although power-hungry!) was using 3 5763's in a low-power or 2 5763's and then go into a 6146, 2E26, 807 or even an 811. The pentodes allow better interstage isolation and control of how much power-density you allot to each stage. This way you can have an oscillator that is easy on crystals but still has good voltage swing. Then using another 5763 as a buffer allows you to control your drive-level to the PA tube. Finally, if you are interested in building these transmitters, I HIGHLY recommend that you make up a test chassis that has sockets for all of your candidate tubes already mounted with the filament, HV and screen wiring permanently installed. Then, mount your output/antenna coupling (usually PI) components permanently as well. Lastly, put in a few of your least-favorite (but working) meters. Once you have this boilerplate, you can quickly wire up and modify each of the circuits. When you get something you like, then get out that new chassis and your most coveted components and build a nice looking final version. Because all of the afore mentioned base-wiring being already in place, this will save you in the long run allowing you to spend your energy on the operational design details; then the test chassis can even be used to start a receiver etc.
The Conar 400 Transmitter used one 6DQ6B and had a #40 pilot light in series with the crystal. The #40 pilot light is rated at 150ma at 6.3 volts. This series brought back a lot of nice memories. Thank you!
Very nicely done, Mike! Much fun to watch. I guess the lesson is that the MOPA was a better mousetrap. A 6AG7 or 6CL6 oscillator driving the 6DQ6 would perform much better, and not torture the crystals.
Thanks again Mike for another great, and original, thought provoking series. I love the tube stuff. I really like the mods for the HC49/U crystals as the older types are so difficult and/or expensive to get hold of for building older type circuits...could well be a game changer for those of us who do not have FT243's or similar... Dave G0KPZ
I love crystal control but hate how many folks never tune around or even look 100 Hz off frequency for your peanut whistle! CW filters in 70's-90s transceivers are very sharp. Use the RIT. At least with the new panadapter waterfall on SDRs, it shows you that someone is answering.
Looks like series 150 Ohm resistor cracked the problem but not the crystal 😁. Really like the old ads and inserts. Those 1920s crystal price are eye watering. An online calculator indicated $50 in 1927 is about $780 today! Thanks Mike for another excellent video.
Very nice! I've used the HC49/U (tall) xtals I've found on eBay with good results in simple Novice transmitters using a 6AG7 or an equivalent 6CL6 oscillator followed by a pair of 807s or a 6146 PA -- even multiplying to higher frequencies up to 15 meters. But I've also cracked a couple of FT-243 xtals trying to oscillate a 6V6 or 6L6 tube directly. This gives me hope for future projects with my pile of old sweep tubes. Thanks.
So what was the final configuration Mike? Totally stock except for the 150 ohm resistor in series with the crystal? 150 volt regulator back in? Grid leak resistor back to stock? And still the 100 pF cathode bypass cap as shown on the schematic at 5:00 ? I really enjoy your videos Mike! 73, Jim W7RY
Interesting to see how finely balanced the whole system is. A resistor increase at the crystal affects how the tube performs. Could this damage the tube in time or is it that it just won't work quite as well? Thanks for another great video.
I was looking at the plate current and it is lower, so it is starving the tube when just out of tune. I would say the 6DQ6 just laughs. But it has to be spoiling the Q.
An oscillator is tricky enough when it comes to starting reliably and self biasing, but expecting it to deliver significantly more power than normal, and do it without chirp, makes for some trades. But don't worry about the sweep tube. It was designed for a big old TV and 100% duty.
Hah! I knew that little teaser at the end would draw this question. I was not completely truthful on the 813 circuit being the same topology as the 6DQ6. It is actually a TriTet with two tuned circuits, so a different animal. I would start with the biggest rock you can find and get it stable. And regulate the Screen to 150V! Only then would I attempt to use the modern rocks. The suggestion of using two in parallel is a good one to try, too.
I think you are seeing a surplus Watkins Johnson 8711A with the green display. This is a first generation DSP IF back end radio that is still in commercial use, and may actually still be in production, even though it is a late 80's design. On WJs downfall, the company was bought by BAE, then sold again and currently is owned by DRS (Signal Solutions).
I have enjoyed the videos I Live in S.W Cumbria in N.W England UK I Have duel Call signs G0MEJ- UK KG0PL -USA would interesting to get a hold transformer 220 240 Volts AC?
Great series, just in time. I saved mine built from the 1962 Handbook since constructing it in Jr. High shop class,1967, as WN6CAB. This time, i stripped it down and used as many original parts as possible. A definite re-learning experience! I hope to put it on 40 soon. Again, thanks for posting. 73s de WA6CAB
The old crystal cracker lives again! Thanks for enjoying my video time warp!
I have not seen anyone else go into this level of detail. Very good. bill
RUclips provides the flexibility to adapt to the comments and make further investigation easier than with articles and books.
I built several 'power-oscillator' transmitters and every one was a pain and more of a lab experiment depending on crystal and antenna. The best one was a 6146 for stability and output power but you always give up most of what power you could get out of the tube you're using, if it was just a PA.
So, I quickly moved on to using a separate Xtal-oscillator (6C5, 6F6, 6V6, 6AG7, 6J5, 6C4, 6CL6 even 5763) and that made my life soooo-much easier that I never messed with power-oscillators again. [edit: also stole a 6AU6 oscillator design from a 51J that was very stable.] When you use a separate tube and even a buffer; (in fact a 6U8 is an excellent example) to feed a power tube, you can really get a MUCH-BETTER bang out your 6DQ6 or 6LQ6 or whatever sweep tube. So, whIle nostalgic and cute, I never recommend someone build, as I'm sure a lot of novices had difficulty.
The best topology I found and liked (although power-hungry!) was using 3 5763's in a low-power or 2 5763's and then go into a 6146, 2E26, 807 or even an 811. The pentodes allow better interstage isolation and control of how much power-density you allot to each stage. This way you can have an oscillator that is easy on crystals but still has good voltage swing. Then using another 5763 as a buffer allows you to control your drive-level to the PA tube.
Finally, if you are interested in building these transmitters, I HIGHLY recommend that you make up a test chassis that has sockets for all of your candidate tubes already mounted with the filament, HV and screen wiring permanently installed. Then, mount your output/antenna coupling (usually PI) components permanently as well. Lastly, put in a few of your least-favorite (but working) meters. Once you have this boilerplate, you can quickly wire up and modify each of the circuits. When you get something you like, then get out that new chassis and your most coveted components and build a nice looking final version. Because all of the afore mentioned base-wiring being already in place, this will save you in the long run allowing you to spend your energy on the operational design details; then the test chassis can even be used to start a receiver etc.
Agree 100%!
The Conar 400 Transmitter used one 6DQ6B and had a #40 pilot light in series with the crystal. The #40 pilot light is rated at 150ma at 6.3 volts. This series brought back a lot of nice memories. Thank you!
I forgot about those Conar twins. Certainly that was a great example of a commercial version of this.
Very nicely done, Mike! Much fun to watch.
I guess the lesson is that the MOPA was a better mousetrap. A 6AG7 or 6CL6 oscillator driving the 6DQ6 would perform much better, and not torture the crystals.
Yes! And that is where I went with mine back in the 70s after cracking a couple of crystals. I stuck a 6V6 in the case and added some driver tuning.
Thanks again Mike for another great, and original, thought provoking series. I love the tube stuff. I really like the mods for the HC49/U crystals as the older types are so difficult and/or expensive to get hold of for building older type circuits...could well be a game changer for those of us who do not have FT243's or similar... Dave G0KPZ
I love crystal control but hate how many folks never tune around or even look 100 Hz off frequency for your peanut whistle! CW filters in 70's-90s transceivers are very sharp. Use the RIT. At least with the new panadapter waterfall on SDRs, it shows you that someone is answering.
Looks like series 150 Ohm resistor cracked the problem but not the crystal 😁. Really like the old ads and inserts. Those 1920s crystal price are eye watering. An online calculator indicated $50 in 1927 is about $780 today! Thanks Mike for another excellent video.
Very nice! I've used the HC49/U (tall) xtals I've found on eBay with good results in simple Novice transmitters using a 6AG7 or an equivalent 6CL6 oscillator followed by a pair of 807s or a 6146 PA -- even multiplying to higher frequencies up to 15 meters. But I've also cracked a couple of FT-243 xtals trying to oscillate a 6V6 or 6L6 tube directly. This gives me hope for future projects with my pile of old sweep tubes. Thanks.
Oh yes with the 6V6. Especially in my Paraset.
enjoyed--and learned something new!
Glad you enjoyed it!
So what was the final configuration Mike?
Totally stock except for the 150 ohm resistor in series with the crystal? 150 volt regulator back in? Grid leak resistor back to stock? And still the 100 pF cathode bypass cap as shown on the schematic at 5:00 ?
I really enjoy your videos Mike!
73, Jim W7RY
Interesting to see how finely balanced the whole system is. A resistor increase at the crystal affects how the tube performs. Could this damage the tube in time or is it that it just won't work quite as well? Thanks for another great video.
I was looking at the plate current and it is lower, so it is starving the tube when just out of tune. I would say the 6DQ6 just laughs. But it has to be spoiling the Q.
@@MIKROWAVE1 Thanks for the reply Mike, good to know that no damage is being done.
An oscillator is tricky enough when it comes to starting reliably and self biasing, but expecting it to deliver significantly more power than normal, and do it without chirp, makes for some trades. But don't worry about the sweep tube. It was designed for a big old TV and 100% duty.
@@MIKROWAVE1 Understood, thank-you!
How about adding two (or three?) identical crystals in parallel?
It can work but the capacitance goes up and ultimately the oscillator may need adjustment. Plus it might play a flutelike tune!
Could we use a modern crystal on a 813 tube as a mopa transmitter ?
Hah! I knew that little teaser at the end would draw this question. I was not completely truthful on the 813 circuit being the same topology as the 6DQ6. It is actually a TriTet with two tuned circuits, so a different animal. I would start with the biggest rock you can find and get it stable. And regulate the Screen to 150V! Only then would I attempt to use the modern rocks. The suggestion of using two in parallel is a good one to try, too.
@@MIKROWAVE1thank you for replying my question. I was very curious an article that was made by RCA about using 813 tube as mopa transmitter.
Mike- what is the receiver you are using there? I don’t recognize it.
I think you are seeing a surplus Watkins Johnson 8711A with the green display. This is a first generation DSP IF back end radio that is still in commercial use, and may actually still be in production, even though it is a late 80's design. On WJs downfall, the company was bought by BAE, then sold again and currently is owned by DRS (Signal Solutions).
What about adding two, matched crystals in parallel? G7VFY
I can not see why it would not work within reason.
PLEASE DO ONE ON A 6AQ5 MOPA kg6mn
a 6AQ5 MOPA as with a Hartley ECO 6AQ5 feeding a Class C 6AQ5? No crystals?
$30
Hah! Another anticipated comment!
I have enjoyed the videos I Live in S.W Cumbria in N.W England UK I Have duel Call signs G0MEJ- UK KG0PL -USA would interesting to get a hold transformer 220 240 Volts AC?
They certainly made them, so it would not be too hard to find on your side maybe.