I built a 12AT7 regen back in december. It works pretty well other than the loud electrical hum comming out of the speaker. I used a transformer for my audio trans. with a primary winding for 220V and a secondary of 6,50 VCT. The schematic is from www.mines.uidaho.edu/~glowbugs/12at7_regen.html. I run this radio off of a seperate isolation transformer. I just bypassed the one in the schematic. To reduce noise i tried using the EMI filter from an old computer power supply. Could somebody tell me if changing values of the C14 A&B or any other cap would help or is there any thing else i could try.

Is it possible that your capacitor C14 is defective? Also, you say you are using a separate isolation transformer. Is it directly hooked up to the rectifer and filter just as the schematic shows?
How did you connect the output transformer? Seems like you got it right, as the radio has audio output.
Rich

:I built a 12AT7 regen back in december. It works pretty well other than the loud electrical hum comming out of the speaker. I used a transformer for my audio trans. with a primary winding for 220V and a secondary of 6,50 VCT. The schematic is from www.mines.uidaho.edu/~glowbugs/12at7_regen.html. I run this radio off of a seperate isolation transformer. I just bypassed the one in the schematic. To reduce noise i tried using the EMI filter from an old computer power supply. Could somebody tell me if changing values of the C14 A&B or any other cap would help or is there any thing else i could try.

Just a few other thoughts. What is the frequency of the hum.... very low like 60 HZ, or is it higher pitched? Check the regeneration control; you might find that you have it set for too much regen.
Rich

:Is it possible that your capacitor C14 is defective? Also, you say you are using a separate isolation transformer. Is it directly hooked up to the rectifer and filter just as the schematic shows?
:How did you connect the output transformer? Seems like you got it right, as the radio has audio output.
:Rich
:
::I built a 12AT7 regen back in december. It works pretty well other than the loud electrical hum comming out of the speaker. I used a transformer for my audio trans. with a primary winding for 220V and a secondary of 6,50 VCT. The schematic is from www.mines.uidaho.edu/~glowbugs/12at7_regen.html. I run this radio off of a seperate isolation transformer. I just bypassed the one in the schematic. To reduce noise i tried using the EMI filter from an old computer power supply. Could somebody tell me if changing values of the C14 A&B or any other cap would help or is there any thing else i could try.

It is a 60 HZ hum. It becomes stronger when I turn on another appliance like a TV.

:It is a 60 HZ hum. It becomes stronger when I turn on another appliance like a TV.

The caps might be bad. I bought them new. Also would running full wave rectification help performance.

Full wave rectification would help performance greatly. Be sure that your electrolytics are over 20 MFD, and are of proper voltage, and are inserted properly (be sure that diode is inserted properly, too). Is the hum always there or only when you are tuning in stations? If it is always there, then something is wrong with the power supply (most likely). What kind of diode are you using? Is it capable of at least 200 volts both forward and reverse? I do not know what your experience is with these things, so I will question some basic things. For instance, did you by chance use a Zener diode in place of a regular diode? I tried doing this a long time ago when I first started with electronics. A Zener diode, however, can only be used for voltage regulation circuits. It will pass current in both directions, especially when the Zener voltage is approached. This can also damage electrolytics.

If the hum is only present when tuning in stations, unplug all other devices within your home except for incandescent lamps that are not operated from a rheostat. Computers and televisions can cause a 60 cycle hum. Amazingly, I have also found that the surge protectors (interference reducers) can also cause a 60 cycle hum. Wireless internet ruins reception in many ways. Fluorescent lamps can cause both 60 cycle hum and static. Light dimmers cause 60 cycle buzz that is similar to 60 cycle hum, but sharper in tonal quality, sometimes staticy. Microwaves cause static, but usually only when in use. I'd mention mixers and blenders, but they don't do anything unless you're using them, and if you own a fine Sunbeam Mixmaster or Hamilton-Beach mixer from the 1950s or prior, they usually have sufficient noise supression built right into the motor (very fine mixers).

Thomas

When I mentioned surge protector/interference reducer devices, I was referring to the surge protector outfits made for computers that have noise supression circuits built into them. Amazingly I owned one that ruined AM reception. It did not do this when we first bought it, though (as far as I can remember), so it may have been failing). All I know is that AM radio reception sucked when it was on, and plugging the computer directly into the wall did not cause the hum.

Thomas

Thanks for the help guys. I will try the suggestions. Again thanks.

Jeremy

Does the hum change or stop when you disconnect your antenna? I have an indoor "long wire" antenna in my shop. Unfortunately, it runs close to a fluorescent light fixture. Lots of hum, so I have to switch off the fluorescent when I use my crystal set or one-tuber. Full wave rectification won't make much difference if you already have a hum problem. It will change from 60 Hz. to 120 Hz. and may be a little less loud. First priority: figure out if the hum originates in the power supply or outside the radio (picked up by antenna). If neither, then you still have a problem somewhere in the main part of the receiver (detector or amp.). Rich

:Thanks for the help guys. I will try the suggestions. Again thanks.
:
:Jeremy

The hum is being picked up by the antena mostly, there is still a noitiable noise in the background. Full wave didn't do much. Ceramic disk caps should have infinite resistance right? C17 measures 140.7K ohms when its not connected to speaker when it checked it and c16 measures 145K ohms. Is this a problem? I think it is but am not really sure. Am I doing some thing wrong?

Yes... ceramic caps should be nearly infinite. Certainly they should at least be in the megohms. What voltage rating are these caps? Caps intended for low voltage transistor circuits wouldn't support the > 100 volts you have in this circuit. Maybe you zapped them?
I didn't think full wave would make much difference. Probably did increase your output voltage a little.
Rich

:The hum is being picked up by the antena mostly, there is still a noitiable noise in the background. Full wave didn't do much. Ceramic disk caps should have infinite resistance right? C17 measures 140.7K ohms when its not connected to speaker when it checked it and c16 measures 145K ohms. Is this a problem? I think it is but am not really sure. Am I doing some thing wrong?

Sorry for giving the idea that full wave would eliminate your hum problem. I really meant that it would simply improve over-all performance with a properly performing set.

Ceramics definitely have no leakage when good. That you may be using caps rated at too low a voltage, as Rich suggested, could be the very reason for their failure. It is rare for ceramic caps to otherwise leak. Paper caps leak more often, as moisture gets absorbed into the paper, and microscopic oxidation from the aluminum works its way into the oil and paper, and/or any moisture present, thereby causing a leakage trail.

Good luck,

Thomas

Some of the ceramics that i used were used in other odds and ends stuff. I should have checked them before I used them.

Changed the bad caps and now it works really good. THANKS for the help. I learned a lot of what to do and not to do. Thanks again.

Hi Thomas:

I would like to better understand the theroy behind the regenerative feedback receiver.

Can you suggest any good articles / papers on the subject?

Gary

:Full wave rectification would help performance greatly. Be sure that your electrolytics are over 20 MFD, and are of proper voltage, and are inserted properly (be sure that diode is inserted properly, too). Is the hum always there or only when you are tuning in stations? If it is always there, then something is wrong with the power supply (most likely). What kind of diode are you using? Is it capable of at least 200 volts both forward and reverse? I do not know what your experience is with these things, so I will question some basic things. For instance, did you by chance use a Zener diode in place of a regular diode? I tried doing this a long time ago when I first started with electronics. A Zener diode, however, can only be used for voltage regulation circuits. It will pass current in both directions, especially when the Zener voltage is approached. This can also damage electrolytics.
:
:If the hum is only present when tuning in stations, unplug all other devices within your home except for incandescent lamps that are not operated from a rheostat. Computers and televisions can cause a 60 cycle hum. Amazingly, I have also found that the surge protectors (interference reducers) can also cause a 60 cycle hum. Wireless internet ruins reception in many ways. Fluorescent lamps can cause both 60 cycle hum and static. Light dimmers cause 60 cycle buzz that is similar to 60 cycle hum, but sharper in tonal quality, sometimes staticy. Microwaves cause static, but usually only when in use. I'd mention mixers and blenders, but they don't do anything unless you're using them, and if you own a fine Sunbeam Mixmaster or Hamilton-Beach mixer from the 1950s or prior, they usually have sufficient noise supression built right into the motor (very fine mixers).
:
:Thomas

Well, my very favorite book was Alfred Morgan's Boy's 1st Book of Radio and Electronics. However, I do not know if the book describes regenerative operation thoroughly. As far as I can remember from when I used to read and re-read the book in the 1980s and early 1990s, the book does a very good job. The circuit at the end of the book, however, does not work properly in the 1954 edition. I found a circuit that works superbly in Popular Science's Home Workshop Manual of 1930.

I, personally, understand basically how a regenerative receiver works. Still, the thing that always baffles me is how a tube can regenerate a radio signal, and yet the same tube also detects the radio signal. If the tube is rectifying the signal (detecting it), then how does it regenerate this signal in radio wave form, and also vice versa? It must not regenerate the full radio signal, then. I guess it only regenerates the detected radio signal, which would make more sense. Some books make it seem as though the tube actually regenerates an undetected signal. The self limiting nature of the grid leak would have to make the circuit purely a regenerative detector, and not some sort of amplifier of RF currents.

Thomas

Where can i find that issue of popular science. or can some body email me the schematic. The suggested book is very helpful.

:Well, my very favorite book was Alfred Morgan's Boy's 1st Book of Radio and Electronics. However, I do not know if the book describes regenerative operation thoroughly. As far as I can remember from when I used to read and re-read the book in the 1980s and early 1990s, the book does a very good job. The circuit at the end of the book, however, does not work properly in the 1954 edition. I found a circuit that works superbly in Popular Science's Home Workshop Manual of 1930.
:
:I, personally, understand basically how a regenerative receiver works. Still, the thing that always baffles me is how a tube can regenerate a radio signal, and yet the same tube also detects the radio signal. If the tube is rectifying the signal (detecting it), then how does it regenerate this signal in radio wave form, and also vice versa? It must not regenerate the full radio signal, then. I guess it only regenerates the detected radio signal, which would make more sense. Some books make it seem as though the tube actually regenerates an undetected signal. The self limiting nature of the grid leak would have to make the circuit purely a regenerative detector, and not some sort of amplifier of RF currents.
:
:Thomas

That particular book, "Home Workshop Manual," can be found on eBay from time to time. It was issued by Popular Science in 1930. I can also send you the schematic if you wish. The book has several TRF schematics including a high power screen grid set.

Thomas

If you would send me some of the Schematics I would be most gratefull. The High power screen grid, any FM, and Regen. My email is jlkorb@kci.net

Thank you very much for your help.
Thanks everyone at this site for all of the great help!!
Jeremy

:I built a 12AT7 regen back in december. It works pretty well other than the loud electrical hum comming out of the speaker. I used a transformer for my audio trans. with a primary winding for 220V and a secondary of 6,50 VCT. The schematic is from www.mines.uidaho.edu/~glowbugs/12at7_regen.html. I run this radio off of a seperate isolation transformer. I just bypassed the one in the schematic. To reduce noise i tried using the EMI filter from an old computer power supply. Could somebody tell me if changing values of the C14 A&B or any other cap would help or is there any thing else i could try.

Jeremy, if your problem still remains a mystery afte all these great suggestions, check for a ground loop situation. There is an excellent article with an explanation at: www.epanorama.net/documents/groundloop/

Great suggestion, Bill. Common problem with regen receivers. Try to connect all grounded devices to exactly the same physical point on the chassis or breadboard. Otherwise, the inductance of the ground path can cause the circuit to oscillate in a weird fashion. I like the books on regens from Lindsay Publishing. The one by C.F. Rockey is pretty helpful.

Rich

::I built a 12AT7 regen back in december. It works pretty well other than the loud electrical hum comming out of the speaker. I used a transformer for my audio trans. with a primary winding for 220V and a secondary of 6,50 VCT. The schematic is from www.mines.uidaho.edu/~glowbugs/12at7_regen.html. I run this radio off of a seperate isolation transformer. I just bypassed the one in the schematic. To reduce noise i tried using the EMI filter from an old computer power supply. Could somebody tell me if changing values of the C14 A&B or any other cap would help or is there any thing else i could try.
:
:Jeremy, if your problem still remains a mystery afte all these great suggestions, check for a ground loop situation. There is an excellent article with an explanation at: www.epanorama.net/documents/groundloop/