I have built a 3 tube fact similie of a GR-81, except I used a 6SF5, 6C5, and 6V6 as the tube lineup. I have a 150 dc volt power supply hooked to the regen. I can receive sw broadcasts from all over the world, but I cannot turn my regen pot clockwise enough to get good, clear ssb or cw. I can hear them as if they were off in the distance. The +voltage range on my 100K regen pot is 56 volts to 158 volts. I installed a pot from the + voltage supply, and I can turn the voltage range down from 37 volts to 110 volts. Does anyone have any knowledge about how to fix the problem? Any useful info appreciated! I just looked at a previous message from Shinkwkan, in Japan, and he said that 20 to 35 volts is about right for oscillation. He told me to use a 3 feet piece of wire for a temporary antenna, and if the ssb and cw reception improves, that means the antenna has been overloading the receiver. I did that once, with no noticable results! Lenny

Hi Lenny,
Could be that the 6SF5 is just a lousy detector. There's no guarantee what a particular tube will do as a regen detector. You could try a 2nd 6SF5 to see if that helps, or swap the 6SF5/6C5, using the 6C5 as the detector. The original GR-81 works quite well with a 12AT7 as a detector/1st-audio.
Dave - WA6VVL

On most of my regen sets, the REGEN control and the tuning are interactive. You may have to slightly adjust your tuning cap as you play with the REGEN control.

Do you have a vernier dial on your main tuning?

Rich

Thanks for replying! I have the 6C5 as the detector. I had the 6SF5 as the detector oroginally, but swapped them around, as suggested by someone on this site. I have a 6 to 1 reduction drive, sold by Midnight Science, on the main tuning cap and the same on the 45pf fine tuning cap. The radio works great overall. Maybe I will figure it out! Lenny

Did you notice any difference in detector performance when you swapped 6SF5/6C5?? If you wired your "clone" like the GR-81, then the wiper on the regen pot R3 should go to gnd. I think your detector's plate voltage is too high. Your 56V - 158V range suggests the regen pot is not connected between B+ and gnd?
Dave - WA6VVL

I just looked at the online schematic, and the wiper, R3, goes to the plate of the first triode section of the 12at7{V1A}. Are you saying that the ground lug of the regen pot may not be soldered well enough to have a good grounding connection? Look at the schematic!!!!!! Lenny

I am looking at the schematic. If the wiper of the regen pot is rotated to its ground connection, how can you still have 56V on the wiper??? What am I missing in this discussion?? It also goes to V1a's plate through a 100K resistor R2.
Dave - WA6VVL

Dave. Correct me if I am wrong! I believe the current flows from negative to positive, so if the wiper is all the way over on the grounded lug, the negative current would flow from the grounded chassis to the plate of the tube, through the wiper. On the lug, which is connected to the + current, the positive voltage would still be there on that lug to be measured, since the easiest path for the electrons is to the plate, rather than flow through the total pot resistance to the + lug. Does that make sense to you? If not, then try to explain it to me, please? Lenny

Are you saying that it is the upper end of the pot that you have been measuring the 56-158 volt swing as you adjust the pot?

If so, that would explain a lot as to why your radio is not working very well. The upper end is supposed to come straight from the power supply which should not be changing much as you adjust the Regen. pot. unless something is wired wrong.

Is it possible you have the top of R3 wired to the wrong end of R4?

Curtis Eickerman

If I have the 2 outside lugs of the pot wired backwards, should not the pot still work, but by turning the pot in the opposite direction than if it was wired correctly? I am sure that I have wired the radio correctly. It works great, but with poor ssb and cw. I can tune in the world clearly! To answer your question: I have been putting my vom meter leads to the center lug and to the lug opposite the grounded lug . I will double check to make sure r3 is connected to the correct end of r4 later today. Lenny

For a triode detector, set up your voltage divider to give about 10V to 30V. Wind your tickler coil to give the correct amount of feedback with those voltages. That should be no more than a half dozen turns on the ground end of short wave coil.

Decouple the antenna. Less than 5 pf is where you want to be. A grounded grid rf "amplifier" with a 5K pot to controll the antenna input is even better.

Much of the old data on regens is wrong. The voltages are too high and the ticklers have way to many turns. The antennas are coupled way too tight.

It sounds like your voltages are way too high. Forget about making audio volume with the detector. Do that with following audio stages.

You voltage divider will look something like, B+ - 100K resistor - 10K pot - 10K fixed resistor -- to ground. Take the B+ for the plate off the whiper. Try different resistors in in the 100K postion to achieve the voltages I talked about.

This advice may sound odd. The schematic may say somthing else. After making dozens of regens I can tell you my advice is correct. Lindsay books has a couple of books on Regen thoery. I suggest learning the hows and whys of regens and making them based on general rules then cut and try. Building to a schematic might get you close but is not going to be optimal.

Below is what you should see with your voltmeter in various positions (the ellipses) if the pot is wired where the pot is supposed to be wired assuming your power supply voltage is 158. As you turn the pot "Up" (as shown below) the upper measurements should go down, the lower measurements should go up and your power supply should not be changing more than a volt or two.If the pot got connected to the wrong end of R4 your regeneration will get "modulated" by the audio amplifier which will sound really really awful.

Curtis Eickerman

Hi Scot,

First off, having rebuilt a GR-81, I can tell you that the detector portion of the design works OK. His measured range of 56V - 158V on the wiper of the regen pot is probably too high and flies in the face of how that pot is connected between ground and B+.

Secondly, the amount of tickler windings s/b accommodated by the regen pot. I to have built my share of regens. In an interesting experiment, I have four coils wound for the AM BCB. The tickler windings are 10T, 20T, 30T, and 45T with a primary of 150T. In a variety of regens, their operation was transparent with all four coils once the regen/feedback was adjusted.

ALL my regens use an adjustable cap from the antenna to the detector's grid, and that is adjusted for min capacitance. It is easy to over-couple the detectors. The GR-81 uses two antenna inputs - a direct connection to the detector's grid through a 12uufd or what you see is what you get through the antenna link on the input coil. All of my regens use a single tuned coil on the input with a tickler coil.

I think most of his problems will be solved when he "fixes" the regen pot.

Dave - WA6VVL

Now, that`s more like it: INPUT. First of all, I did away with the direct input antenna. I will try to slowly go through this info, and put it to work for me! A lot of food for thought here. Last night, I rewound a coil, and had 5 turns on the tickler. It was spaced about 3/4" away from the tuning coil. I guess with 1 or 2 turns, the tickler would be spaced much closer. The radio had great volume and clarity, but no ssb or cw. I really like the 5pf antenna tuner cap idea. I built a 1 tuber by Dr. Greg Latta, and the 5pf antenna decoupling cap really worked.Thanks for this info. Curtis: Thanks for the schematic . Scott: Can you give me a site where I can see the 5k pot grounded rf amplifier setup, which you said would be a great antenna decoupler? Or, maybe post a drawing of the setup here? I really like my radio, and want to make it as good as possible! Let me clarify something here. I have the 168 +voltage hooked to the pot lug, which would be the top lug on the schematic. The bottom lug, shown on the schematic, is connected to ground, and the wiper is connected to the tickler coil and plate of the triode. Is that correct? Lenny

Hi Lenny,
This might be an obvious question, but how did you verify the correct connections of the tickler coil??? With it connected to the wrong phase, the radio will work and you may here lots of stations. Reverse it, and now the detector will oscillate with the regen control. The right connection is where the stations are the loudest.
Dave - WA6VVL

I can hear a shooooop sound, as what I think is the regen, kicking in. I set the regen at max, and when I hear a loud noise,while I am tuning the tuning cap, I reduce the regen, and the station will come in clearly. So. I thought that it was working pretty well. Just under what I think is the regen threshold, is when the station comes in clearly Let me state this again, and maybe someone will take the time to answer this question. If you are looking at the Heathkit GR-81 schematic online, I have the 168+ volts hooked up to R3 at the top lug of the schematic representation of the regen pot. I have the plate and tickler coil hooked to the center lug, and I have the ground connected to the bottom lug, as pictured in the schematic. Is this correct? If not, will you invision your looking down the tuning rod{the front side, with the tuning rod sticking out} of the 100k pot, and which connection goes to the left, center, and right lug?......Lenny

That sounds OK, yet the measured range of 56V - 158V doesn't (measured from the wiper to gnd).
Dave - WA6VVL

That sounds right and matches what I hear in the 12AL8 regen.
I think it woild be more effective if you set regen to 'right at' the onset of oscillation, tune for zero beat, and then readjust regen for best reception.
The problem is, assuming we correctly understand what you meant to say, if the circuit is wired as described then the voltages cannot be what you say was measured. And it doesn't matter what the end device is or how it operates because it's basic Ohm's law. I.E. If the pot is wire as described then when the wiper is rotated fully to the ground position it will be at ground and not 56V.

So either I didn't understand the description, or the measurement is not as thought, or the circuit is not wired as thought, or something is defective because, as described, 'the range' cannot be 56V - 158V unless, maybe, you're measuring relative to B+. I.E. the 'drop' across the regen pot.

As a newly minted 'first time' newbie to regens myself I'd just like to say that Scott's post is a goldmine of information and matches what I discovered 'the hard way', so to speak.

For shortwave I use a gimmick antenna coupling; three or 4 turns of one clip lead wrapped around another clip lead.

As of several hours ago, I have dismantled this radio, and will try another version of regen radio, in hopes that the outcome will be more satisfying. Thanks again! Lenny