Josh, I don't know what you mean by tropical fish capacitors but some capacitors are quite sensitive to noise pickup, as you describe, especially in high gain audio circuits like this one. This is th
This kind of capacitor: http://s337.photobucket.com/user/jusepics/media/Tropical_Fish_Color_Chart.png.html http://www.electrojumble.org/TropFish_a.jpg cracked. Think its worth replacing them? I'm abo
Oh Josh, now I see why you called them tropical fish!! Get any cracked capacitor out of your circuits as quick as you can handle a soldering iron! But have replacements of tubulars on hand first. Cra
If those are cracked, I guess I wold replace them. They likely will not fix the hum but should not be left if cracked. Gary Sent from my iPad _______________________________________________ TenTec ma
My shielding attempts made no difference. I also unbolted the transformer so I could move it around slightly (as much as the leads would allow). That had no effect. I think my next step will be to re
You might want to try and find where the hum is entering the system. I have done this before by using a 1uf cap to ground and touching the cap to the input of each stage. Remember to discharge the ca
OK, this is beginning to sound challenging. First off, I have a parts cadaver C21 that has all of the power supply intact so we have a parts stream. What if I were to send this to you and you could p
Hi Gary, Thanks for the offer! I may take you up on that pending the outcome of my next round of work. I'm going to replace all the cracked capacitors - found a couple more, one of them on the power
Just noticed this C21 Digital on eBay: http://www.ebay.com/itm/Working-made-in-USA-DIGITAL-Ten-Tec-Century-21-with-a-keying-issue-/232358014086?hash=item36199dec86:g:dzkAAOSwAPVZMaJ3 "Although there
Do the bridge replacement before you evaluate the transformer on the bench. That way, you don't mask one problem with antother. A good rule of troubleshooting is change ONLY ONE THING AT A TIME. Keep
I'm not an electronics whiz. But to me, if you're getting the noise in headphones but not in the speaker, it sounds like the headphone cord is picking it up. If you have cracked capacitors in the pow
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
Try grounding ground side of speaker to ground from power supply. If hum is still there there is a 4.7 ohm resistor that might be shorted Or a 270 uf cap open both feed the audio amp Byron Cordes ___
All direct conversion receivers are going to have some hum unless you have a DC only power supply (batteries). Stuart Rohre K5KVH _______________________________________________ TenTec mailing list T
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
The print I looked at had the 4.7 ohm and a 240 uf cap to filter the 12 volt supply to the audio amp. Normally the resistor would open up but it's a chance. A choke would be a better choice but cost
Do try other head phones to see if you find ones less sensitive to the Direct Conversion hum component. One trick is to front the phones with an audio filter picked to null the hum frequency. You cou
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
I haven't used my Century 21 for quite awhile. For a few years it was my main rig (3-4 years ago). I don't remember there being any objectionable level of hum. I did use an impedance converter when u