Hi Chris, The hum is present in the speaker, just not so noticeable because it is much less sensitive and much further from my ear. I suspect the speaker is less responsive to frequencies below 120Hz
Thanks Byron. Grounding to PS ground had no effect. I don't see a 4.7 Ohm resistor anywhere... are we talking a resistor on the audio board? Here is the schematic for the audio board: https://drive.g
You may be right Stuart, it may just be a characteristic of the radio. Several people have said that now. I have no other C21 to compare it to, but it sounds excessive to me. I will keep at it for a
I figured out the 4.7 Ohm resistor and 240 uF cap. You must have been looking at the Century 22 schematic. It uses the same LM380 as the Century 21, BUT it has additional filtering on the 12V feeding
Just when you thought this thread was done... some interesting new information! It seems that Ten-Tec started adding in additional shielding for the transformer at some point. Mine does not have the
Thanks Carter. I tried some shielding using some thin steel I had, but I want to replicate the shield that Ten-Tec used. They must have done that for a reason! It turns out that my C21 digital is a v
I'm learning a lot about shielding... tons of good resources on the Net. This article was particularly useful: http://www.ets-lindgren.com/pdf/emctd_1293_weibler.pdf The fact that Ten-Tec used alumin
I agree Carter. Here is another thought... perhaps its a heat-sink, and not a shield? That would explain the use of aluminum. Now that I think of it, when I removed the transformer there was a square
Very good info, thank you! Check out this neat article from 73 Magazine, Dec. 1977: https://archive.org/stream/73-magazine-1977-12/12_December_1977#page/n29/mode/2up There is the man himself, and a p
Hi Mike, You can use either the ACC1 or the regular key jack. The output of an external keyer looks just like a straight key to the radio. I'd probably use the key jack since the required cable is ju
Hi Curt, I didn't mess with the bridge rectifier. When I removed the transformer from the chassis, the noise went away. I've made a shield out of steel for the transformer, but have not yet had time
Huge thanks to Ed, W3NR, for sending this to me! It is a hand written letter to 'Tom' (not sure who this is) from Ten-Tec dated Feb 13, 1978. "I also have a hand written how-to on adding a pre-amp to
No need to resort to Wayback machine... searchable archive of this list is here: http://lists.contesting.com/archives//html/TenTec/ This info is included at the bottom of every email that is sent out
You mean like this page here? https://www.tentec.com/?page_id=143 "The service@tentec.com email is monitored Monday through Wednesday. At this time we are unable to offer extensive telephone or email
Greetings Ten-Tec List, I just recently bought my first Ten-Tec rig - a Century 21/ Digital. I really like the radio and I'm having a lot of fun with it! The one fault I've found with it is a loud hu
Hi Gary, I attempted to measure the audio output on the scope. I measured it both on the internal supply and on external. This is with the volume pot turned all the way down so all you hear is the hu
Hi Gary, Yes, I hardly need to turn the volume up at all when listening to normal signals. There was something in the Ten-Tec manual about an 'attenuation network' for the phones to suppress noise. I
Hi Dan, The manual says I should be using 8 Ohm headphones, which is what I am using. I tried the swamping resistor that Gary suggested. 220 Ohms knocked the hum down to where I almost can't hear it
Stuart, Aside from pulling the bridge rectifier out and testing each diode, is there a way to tell if one of the diodes is open? I'm trying to visualize what having one open diode would do... wouldn'