In the early 1970s I built several science kits offered by a company in San Antonio, TX called the American Basic Science Club (ABSC). The one shown above is a three tube regenerative receiver for either the MW BC or 80 m Amateur band, depending on the coil taps used. I am trying to bring it back to life but have no schematic or other documentation. Over the years three resistors have come loose at one end, as have both wires to the primary side of the transformer for the matching speaker. The schematic shown below is the result of me looking up some vintage-tube data and trying to trace the circuit. I welcome any informed suggestions for how to connect anything labeled with a '?'.
The ends of the 560K and 1M resistors go to a "B+" supply, (probably in the range of 150vdc to 250vdc). The 150-ohm resister at the cathode of the 35C5 goes to ground. The speaker wires connect to the output at the bottem of the audio transformer at lower-right corner of the schematic. Hope this helps.
ReplyDeletemronne2
ReplyDeleteIf you look at the schematic you will see the 560 K is already tied to the B+ (top of the 22 uF capacitor).
The transformer at the lower right is a power transformer. Blow up your speaker doing what was suggested.
This schematic does not show the B+ return and I suspect the end of the power transformer secondary marked GRN should be tied to ground.
In this circuit the 35W4 functions as a half wave rectifier with B+ coming off a pi filter made up from the 33 uF, 150 Ohm and the 22 uF.
The ? at the bottom of the 150 Ohm should tie to ground.
What voltage do you read across the 22 uF capacitor?
ReplyDeleteBruce, thanks for pointing out the pi filter. I had not spotted that but it should be more conspicuous in my next rendering of the schematic.
ReplyDeleteAC voltages on secondary:
GRN-YEL 32 V
YEL-RED 51 V
GRN-RED 83 V
DC voltages on electrolytics:
22 uF 117 V
33 uV 117 V
I am surprised by how the capacitors can have a higher voltage than the highest found on the secondary unless it can be explained by the AC measurements representing the average over a cycle while the capacitors hold a peak value after rectification.
I wish I could give you advice on where your speaker ties in. I think mronne2's advice that the ends of the 560K and 1M resistors go to a "B+" supply may be a good clue.
ReplyDeleteI'm going to throw out a few ideas.
You have 117 VDC on one end of the 560K and the 1M pot should be at that voltage also. The remaining ? on the resistors could be tied together. That should not hurt anything. Maybe the primary of the speaker transformer goes between them??????
The primary of the speaker transformer would typically be in series to the plate of the 35C5 (pin 7). This would require you to lift the .01 cap and choke from pin 7 and tie them to one speaker primary and then the remaining speaker primary would go to pin 7 of the 35C5. The 35C5 is your audio amplifier but I am not sure how it gets the audio. The input would be the control grid on pin 2 of the 35C5 but all I see is that it has a bypass capacitor and a 560 K for biasing.
Thanks Bruce. What you have said here supports conclusions I have been drawing from looking at other regen schematics from that era. This project is slowly coming together. Within a few days I should post a revised diagram, not so much of how the radio was originally, but of where I think I should go with it.
ReplyDeleteI have the original manuals for this if you want the schematic
ReplyDeleteThis comment has been removed by the author.
ReplyDeleteHow do you post a JPG here, trying to give you the schematic but this sight is not very user friendly.
ReplyDeleteI posted it on Facebook in (Ham Radio, The Old Days)
ReplyDeleteThank you very, very much David. I knew there had to be someone out there who still had an instruction manual.
DeleteWow -- nostalgia trip! I had kits 1, 2 and 3 myself in the early 70s. The neon strobe light and the "mystery" shock box were very cool. About the only parts I still have left in my junk box are the induction coil and the potentiometer knobs. I wish there was more info on these kits on the internet.
ReplyDeleteI remember that shock box, Mark. When my parents had visitors I used to leave it around for them to learn to keep their hands off my stuff. I still have parts from the cloud chamber, spinthariscope, spectroscope, telescope, photographic enlarger, microscope camera.
DeleteDid you learn about ABSC kits the way I did -- from adverts in comic books, back when they were regarded as trash for young minds?
Yup, I found out about them from comic book ads too. I was living in rural Quebec at the time, and my Dad had to drive me 20 miles to the nearest customs office to pay the duty on them.
DeleteYou've inspired my latest post. I hope it brings back some fond memories.
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