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 Post subject: 5 Tube Regen
PostPosted: Dec Wed 27, 2017 4:25 pm 
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Joined: Oct Thu 13, 2011 8:26 pm
Posts: 282
Location: Isanti MN
Last Fall I asked for ideas on building a regen receiver. This is what I came up with.

This is my marked up schematic. Not sure who sent the original, but thanks. The VR tube was replaced by 1N4747 zener diodes, Mouser was selling them for .03 each. The RF tube, 2GK5, was found in a collection of TV tubes from an old tube caddy I purchase at an auction. It seemed to be the best RF triode tube I could find. The PA stage will eventually be place in the separate power supply.

For now the regen seems to work well with head phones.

Attachment:
5 Tube Regen My Version.pdf [65.58 KiB]
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This is a picture of the front.

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5 Tube Regen Front View (400x300).jpg
5 Tube Regen Front View (400x300).jpg [ 98.14 KiB | Viewed 1290 times ]


And, more importantly this is a picture of the insides.

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5 Tube Regen Top View (400x300).jpg
5 Tube Regen Top View (400x300).jpg [ 115.01 KiB | Viewed 1290 times ]


So now the tinkering begins. I have noticed that by touching the 6SK7, metal tube, a lot of background noise goes away. I wonder if pin 1 is a connection to the metal shell. My tube manual doesn't say.

I did put a heavy wire jumper around my well pump, there are plastic vibration dampening pipes between the well and the tank, so now I have a good ground to the well. That made a huge improvement in my S-38 radio reception.

Also, now noticed that my QRM trap isn't working as it should. Maybe the better ground changed that. Any ideas?

It is winter here and more that 20 below zero. Good day to mess with the radios. Thanks for all the advice earlier. Any more new comments will be greatly appreciated. I'm learning as I go.


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 Post subject: Re: 5 Tube Regen
PostPosted: Dec Wed 27, 2017 4:46 pm 
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Location: Wayside, NJ Monmouth
Looks Great, As for the 6SK7, Pin 1 is the shell and internal shield and can be grounded. The weather here on the East coast is not to bad. But cold enough for me to stay in the basement, get the wood stove going. I am at work today, inventory, but will be off till Jan 2dn. So for the next five days, I will be in the shop / shack working on radios and playing on the Ham bands. Life is good.


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 Post subject: Re: 5 Tube Regen
PostPosted: Dec Wed 27, 2017 8:10 pm 
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Location: SoCal, 91387
tjugofyra wrote:

For now the regen seems to work well with head phones.

Your print show a speaker; how does it work with that?

I built a 3 tube regen last year powered by batteries, and it gives ample speaker volume. In fact, it doesn't even have a headphone connection. I did a thread on it, LMK if you would like me to post the link.

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 Post subject: Re: 5 Tube Regen
PostPosted: Dec Wed 27, 2017 9:44 pm 
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Joined: Oct Thu 13, 2011 8:26 pm
Posts: 282
Location: Isanti MN
I've Xed out the PA on the schematic and drawn in a phone jack. Next need to get the QRM trap working to get rid of my nuisance clear channel station that comes in over everything. The station is only 15 miles away. Sometimes it is handy as a signal generator.

Last spring, the QRM trap tuned the nuisance station out just fine, but that was on a different radio. Now I have to back track and figure out what changed. Probably something with the antenna impedance or the change in ground. This front end stuff is a mystery to me. The 5 tube regen radio input impedance is a 2.7K resistor; right? No tuning on the input.

I did ground Pin 1 of the 6SK7, That helped. Probably should ground pin 1 of the 6SJ7 also.

I built a separate Power Supply in another box. Eventually, I plan to put the audio power amp in that box. Maybe will use a 6V6 or whatever I find that's suitable. There are some other filter circuits that might workout in that PS box also.

The detector is getting stations with only 5V on the screen grid. Is that really low or about right? I'll bet a weaker station might require more voltage for more detector amplification.


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 Post subject: Re: 5 Tube Regen
PostPosted: Dec Thu 28, 2017 1:21 am 
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Joined: Dec Sun 14, 2008 3:33 pm
Posts: 673
Location: Tokyo
5 volts on the detector screen is not abnormal. Triode regenerative detectors work at low plate voltage, and the 6SJ7 screen is the equivalent of a triode plate. If you reduce the 6SJ7 plate voltage, you'll find you have to increase the screen voltage to get it into oscillation. The advantage of a higher pentode plate voltage is more audio gain.

You can replace that 2.7K cathode resistor on the 2GK5 with a 2K pot, the antenna going to the wiper. Makes a very useful RF level control. Sometimes reducing overall RF level and increasing regeneration improves selectivity.

I notice your RF filter is .001/2.7K/.001. I also like to use a resistor rather an an RFC for that. I usually use a higher value resistor, around 10K. I think 2.7K is a little low for the bottom of the AM BC band. Also, it's more typical to see the filter between the plate and the plate load resistor. IOW, connect the 100K resistor to the .01/.001 node on the volume control side. Why? Decouples RF out of the power supply.

I see you have a 1K grid blocker for the 6K6, but none for the 6SK7 audio amp. How about a 4.7K~10K blocker on the first audio amp control grid, and maybe add a small cap from control grid to ground (around 100pF~300pF to taste)? It provides additional RF shunting to ground, and knocks off some hiss.

Rob


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 Post subject: Re: 5 Tube Regen
PostPosted: Dec Fri 29, 2017 9:42 pm 
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Joined: Oct Thu 13, 2011 8:26 pm
Posts: 282
Location: Isanti MN
Thanks for the info and tips. I value that very much.

The 20 volt tap might be a better choice if the 6SJ7 screen works around 5 volts. Thinking the wiper resolution would be better working off of 20 volts instead of 40. Anyway, easy to change. Resolution is why I put that extra 2.5K pot in series with the 100K, It is a dual pot. Plan to take out if there is not benefit.

The 2.7K cathode resistor can be changed easily. I found a small, 1 inch dia, 3K pot designed to be set with a lock nut. I also found a good Ohmite 2.5 K pot that could be fastened to the front panel. I havn't installed either, yet. Is this a variable that will be changed with the tuning, or will it be set in a more or less permanent condition?

I see the advantage of changing the filter. Also saves a .01mFd cap.

Is the grid blocker to limit positive grid current flow? Not at all familiar with that term or function. I can see the high freq filter effect of the capacitor. Some more explanation would be helpful.

Lyn


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 Post subject: Re: 5 Tube Regen
PostPosted: Dec Sat 30, 2017 2:36 am 
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Joined: Dec Sun 14, 2008 3:33 pm
Posts: 673
Location: Tokyo
Lyn, the pot is adjusted as conditions warrant. The setting varies with frequency, antenna, and signal strength. There's a good discussion of why this control is necessary in Sturley's Radio Receiver Design, Part 1. Go to the chapter on different types of AM detectors, including regenerartive. That book can be downloaded here:

http://www.tubebooks.org/technical_books_online.htm

Btw, the value of that pot (as a cathode resistor) is not very critical for a GG amp. Generally, something between 1K to 5K seems to work fine.


Sorry, I should have used the correct term, 'grid stopper', not 'grid blocker'. One of its functions is to limit positive grid current, but it seems if your bias is greater than about -1V, it's not a concern. Here, the main thing is to make, along with the control grid-cathode capacitance, a low pass audio filter. Shunts any remaining RF to ground. RF level at the audio amp control grid can be surprisingly high, even after the detector's own RF filter. That RF can work itself back to the detector input, creating problems. It also can lower audio gain.

You can calculate proper values for the resistor, taking into account the control grid-cathode capacitance. But what I do is use a resistor between 4.7K~10K, and then add small caps, grid to ground, 'to taste'. Small being in the 30~300pF range. I like taking the edge off the 'hiss'. Btw, strictly speaking, a grid stopper should be a carbon resistor, not metal film or oxide, and certainly not wirewound.

Rob


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 Post subject: Re: 5 Tube Regen
PostPosted: Jan Mon 01, 2018 5:53 pm 
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Joined: Oct Thu 13, 2011 8:26 pm
Posts: 282
Location: Isanti MN
Rob,

Read the section, page 393, in Radio Receiver Design. Makes sense and, not only that, it works.

Snooping through my stuff, I found a 2.5K pot that actually measured 2.7K. Reducing / controlling the RF gain reduces the signal strength of the strong station, then allowing the regen control to compensate and bring in a nearby station. Right now the radio is working quite well into headphones right above my strong nuisance station. It is daytime now. Can't wait to try it tonight. Air should be cold and crisp too.

I changed the RF filter as you described also, and put in a grid stopper on the 6SK7. Haven't added a small filter cap to the grid yet. I had planned on putting a band spread capacitor in parallel with the main tuning capacitor but the new RF gain control is taking up the hole. Tuning is touchy. Next problem is to, somehow, add a band spread. The present tuning cap in the radio is kinda stiff and clunky. Then, eventually, build the audio power amp.

I had the tubebook site in my favorites already but didn't realize the wealth of information in that site, especially the Sturley book. Need to spend more time looking through the book and the site. Also on page 340, second paragraph, Sturley alludes to the future of solid state devices by referring to copper oxide and other crystals. The book was published in 1943, wonder if people were already looking over the horizon. I am sure they were. Good book, good tips and advice, thanks.

:yn


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 Post subject: Re: 5 Tube Regen
PostPosted: Jan Tue 02, 2018 2:17 am 
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Joined: Dec Sun 14, 2008 3:33 pm
Posts: 673
Location: Tokyo
Also take a look at Zepler, The Technique of Radio Design, same site.

Another very good UK writer on radio is M G Scroggie ('Foundations of Wireless' and 'Second Thoughts On Radio Theory'). Unfortunately, these two books are not available online. Well, Foundations is, but believe it or not, it was uploaded without any of the diagrams, schematics or graphs! Scroggie is really an excellent technical writer: gets right to the heart of the matter, does not lose the forest for the trees, and does it in a very engaging way.

Btw, for fine tuning (I wouldn't say for bandspread tuning), the old '1N4007 used as a varicap' trick works very well.

Rob


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 Post subject: Re: 5 Tube Regen
PostPosted: Jan Tue 02, 2018 4:38 pm 
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Joined: Oct Thu 13, 2011 8:26 pm
Posts: 282
Location: Isanti MN
Thanks again, Zepler is downloaded, that was easy, right off of google. Think I will look for a copy of M.G. Scroggie on Amazon or sum such. Looks like there were many editions so should be able to find a copy. Don't have a lap top so a real book is still more portable.

I was wondering about the vari-cap idea. My friend used a 1N4007 in his SS regen. I experimented with a Radio Schack power diode, rated 3A, 50V, I think, package long gone. Anyway it did work in a FET oscillator. I may give that vari-cap idea a go. Have to look for a '4007 or one in the series. That dual pot idea, intended to be used for fine tuning the regen voltage may have a use with the vari-cap. Mmmm, it is a 2.5K. Seems like things are moving that way.

The variable cap is really stiff, it takes both hands to turn it slightly. So "fine tuning" is a must have. BTW, I did receive New Orleans last night, but the call sign was ESPN. So it could have been a more local re-broadcast. Also now have a 60Hz hum. Not sure where that is coming from. I accidentally soldered the ground end of the RF gain control to the filament and turned on power. I wonder if that could have messed up a tube. I have a good Hickok tube tester. Guess I should check the tubes for shorts.

Lots of stuff to do. Lyn


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 Post subject: Re: 5 Tube Regen
PostPosted: Jan Thu 04, 2018 1:12 am 
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Location: Tokyo
Lyn, Scroggie took over Foundations of Wireless sometime in the 1940s. Someone else had been writing and rewriting it. Sometime, say 1960 or so, transistors made their appearance. And sometime much later, with Scroggie retired, other writers took over. The last editions were much fatter, like college textbook size.

I'm interested in vacuum tube technology and only reluctantly accept solid state as unavoidable. I prefer the older editions. My copy of Foundations is 1957. Small and compact.

Rob


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 Post subject: Re: 5 Tube Regen
PostPosted: Jan Fri 05, 2018 7:38 pm 
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Joined: Oct Thu 13, 2011 8:26 pm
Posts: 282
Location: Isanti MN
The regen seems to be working fairly well. I've logged a few interesting stations. WLW, 700KHz, Cincinnati, for example. That station is something like 700 miles distant. Seems like the RF gain control is at max on the low end of the BCB, where in the high end, there is better performance with less RF amp gain.

Put a decade box into the RF filter circuit and settled on a 33K resistor. The fidelity is fairly good using that value.

The variable cap was changed out for a two part unit that has a concentric shaft. The main capacity value is 280pFd, and a single plate, controlled by the inside shaft, varying the capacity over a 10pFd range. That arrangement seems to work well on the low end of the BCB, but still touchy on the high end. Lots of scratchiness until the sliding surfaces wore in. Hard to know when the last time that cap was in service. Contact cleaner helped and some thin oil.

I seem to be drawn to the vacuum tube technology also. I will eventually get a copy of Foundations by Scroggie. I will probably get an earlier edition as you suggested. I learned electronics in the early '60. Kind of a transition time from tubes to transistors. The electronics class purchased an RCA tube manual, then purchased the book Transistors by Kiver. My career involved solid state stuff but, when I retired, I vowed to go back and figure out what I had missed.

Both technologies have their place. Also, have been drawn to understand history. A story: at a swap meet, I was rattling on, with friends, about oscilloscopes; always thinking they were developed in the 40's along side radar with the CRT. This tall thin man walked up and corrected me, with authority, saying that the CRT was much earlier in the 1990's, I think that is what he said. I was dumbfounded and there resulted an awkward moment. My friends didn't say much to keep the conversation going either. The man said his name was Wolf. I have never seen this person again. I think an opportunity was missed. Physicists were probably working with particle accelerators very early. Somehow they knew the mass of the electron and proton, etc.

BTW, light emitting diodes were noted in the 1900's: Early anyway. Some of the early crystals were biased with batteries and some gave off light.


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 Post subject: Re: 5 Tube Regen
PostPosted: Jan Fri 05, 2018 7:40 pm 
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Location: Isanti MN
oops 1890s, maybe even earlier than that.


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 Post subject: Re: 5 Tube Regen
PostPosted: Jan Fri 05, 2018 7:49 pm 
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tjugofyra wrote:
Seems like the RF gain control is at max on the low end of the BCB, where in the high end, there is better performance with less RF amp gain.

That's exactly how my three tube regen performs. As I tune upward from 540 kilocycles, I have to gradually adjust the gain control down, from fully to eventually about a quarter on, at 1600 KC.

Also, I've noticed that if I have an AA5 next to it and tuned to the same station, when it's on, it increases the volume of the other set. Almost like having a tuned loop.

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 Post subject: Re: 5 Tube Regen
PostPosted: Jan Sat 06, 2018 1:55 am 
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Location: Tokyo
CRTs in the 1890s? I find that hard to believe. The de Forrest audion appeared around 1900, and then it took time to discover what could be done with it. CRTs have grids, plates and cathodes.

But, wha'd'ya know! I just checked Wiki and there was a cold cathode ray tube in 1897:

https://en.wikipedia.org/wiki/Cathode_ray_tube

by Braun, and by the way, that's what a CRT type TV tube is called in Japanese. Another btw: Scroggie wrote a column for a UK electronics magazine during the 1950s and 60s. His pen name was Cathode Ray. Second Thoughts... is a collection of these articles. It's a very interesting book and it's a shame it's not well known. And somewhat rare.

I have to point out that Foundations of Wireless is a radio 'foundations' course. If you've had a career in electronics, you probably won't find too much that is new. Nonetheless, I enjoy reading it. He often makes very pertinent observations and connections other writers miss.

Fifties points out an interesting regen phenomenon: when you tune a regen to the same frequency as a superhet, the latter's signal strength and selectivity sometimes increases. What's happening is the regen is acting like a Q-Multiplier, albeit without a direct connection. You can directly connect them (regen antenna terminal to superhet antenna terminal) and the effect is much more dramatic. Of course, don't directly connect to an AA5 type superhet. If the regen has an isolating RF stage, however, the effect will be much weaker.

Rob


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 Post subject: Re: 5 Tube Regen
PostPosted: Jan Tue 09, 2018 10:21 pm 
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Joined: Oct Thu 13, 2011 8:26 pm
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Location: Isanti MN
I managed to find Foundations downloaded it. I was fascinated by radio in school and, as things go, I got into other more industrial areas of electronics. Another reason to revisit radio and tube now.

Ha, Cathode Ray, I get it. Googled Second Thoughts by Cathode Ray and found some stuff. Now working on a way to download to windows and transfer to my tablet which is android. SanDisk makes a thumb drive with a std USB and micro USB connector in the same drive. Tablet doesn't see the drive, yet. May have to take the tablet to the store and let the boys figure it out.

It may be that those early ray tubes were the predecessor to the particle accelerator, CERN. A friend has the opinion that solid state came first with the crystal sets and the vacuum tube development era was a diversion (detour) from progress in Solid State. After reading the CRT development articles, it seems those early CRTs were important in understanding the electron, proton etc. and the atom. Then came the solid state stuff. Kind of a chicken and egg thing, which came first and what was the progression. I found the Japanese translation and saw the cold part. Cool!

The regen seems to be working quite well. The stations still keep piling up on each other. Thinking that the regen needs more selectivity. Seems the distant stations are, of course, weaker and they are the stations of interest assuming they are farther away.

Fifties, what is that technique where there is a parallel LC circuit that improves signal strength or is it selectivity? Could any parallel LC circuit work? The new variable cap doesn't tune as well as the first one. The fine tune ability is still too broad. The old variable cap had a taper built into the stator also. Next plan to go back to the first variable cap and try the vari-cap diode idea or try a small variable cap added as an outboard, just to try it. I have a few small V-caps to try. Need more improvement if possible.


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 Post subject: Re: 5 Tube Regen
PostPosted: Jan Tue 09, 2018 10:26 pm 
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Joined: Oct Thu 13, 2011 8:26 pm
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Location: Isanti MN
Fifties, just notices you mentioned that you drove a speaker with the last tube instead of head phone. Just now figured out what LMK means. Ya, show me. The headphones I'm using aren't very comfortable. Lyn


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 Post subject: Re: 5 Tube Regen
PostPosted: Jan Tue 09, 2018 10:39 pm 
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viewtopic.php?f=12&t=311565&p=2605799#p2605799

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 Post subject: Re: 5 Tube Regen
PostPosted: Jan Thu 11, 2018 5:38 pm 
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Joined: Oct Thu 13, 2011 8:26 pm
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Location: Isanti MN
Interesting that you showed that circuit. A bunch of ideas clicked on when I saw it. I have a Superior Instruments signal tracer that uses those 1Volt tubes. It wouldn't be very difficult to rewire it with a phone plug and use it as a general purpose audio amp.

I also built a neat battery box for the battery powered radios except it has a six volt filament and 45 / 90 volt B+. Series heater string, maybe.

Real nice job on your regen, and more food for my next regen.


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 Post subject: Re: 5 Tube Regen
PostPosted: Jan Thu 11, 2018 11:53 pm 
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Location: SoCal, 91387
tjugofyra wrote:
Interesting that you showed that circuit. A bunch of ideas clicked on when I saw it.

That's a good part of what this board is about, generating ideas.

tjugofyra wrote:
Real nice job on your regen, and more food for my next regen.

Thx, glad you liked it. Of course you'll be displaying your next project here? :wink:

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