Ten-tec Century 21 restoration

Discussion in '"Boat Anchor" & Classic Equipment' started by HAMHOCK75, May 9, 2016.

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  1. KN4UD

    KN4UD Ham Member QRZ Page

    I have the C21 operation manual and along with the information I have found here I am making head way. I have some push pull pots with short and long sleeves but they are 500k for guitars (mostly Fender) but I don't have any in the 1k range that is where I had the problem. I have 2 1k pots with switches coming that have short sleeves but I can make an adapter to screw on them and also be a spacer that will work as the original pots did. I had checked cts first thinking that was possibly what was in the rig but could not find a match but the ones I have on order will work but won't be the oem like I wanted, to keep it original. Thanks for the information you can never have too much information.
  2. W9GB

    W9GB Ham Member QRZ Page

    Mouser has “In stock” two CTS candidates at 1K ohm with SPST switch (Type TGC, Rotary).
    Switch ratings: 6 amps @ 125 volts AC ; UL & CSA recognized. $5.24 each.

    CTS 450T328S102A1C1 - Slotted (Shaft Trim)

    CTS 450T328F102A1C1 - Flatted (Shaft Trim)

    CTS 450 series data-sheet (circa 2015)
    NOTE: CTS sells a 450G series of 24mm rotary potentiometers.
    Series designed for guitar manufacturers/restorers (Thin profile, high resistance values).
    Last edited: May 7, 2018
  3. KN4UD

    KN4UD Ham Member QRZ Page

    Thanks for the great information . The 2 pots I arrived 3 days ago and now I have it up and running. Been listening around on the band's and the only problem I have is the noise on the audio amp, I know the lm380 has plenty of power but it is a little on noisier side. I have used the lm386 before and if it was not clean I could usually put a 220mf from the vc to ground and cure the problem. Tried this on the lm380 and it did not change but I can live with it. Thanks for all the help guys.
  4. HAMHOCK75

    HAMHOCK75 QRZ Member

    Is the noise a specific frequency like a hum or is it more like white noise, a hiss? WU7H has examined line related noise getting into the audio pretty extensively. In that case, the hum became significantly more noticeable with headphones.
  5. WU7H

    WU7H Ham Member QRZ Page

    Mine has a lot of noise too, but it all clears up when I run on external 12V. I tried all sorts of things to kill that noise, but nothing worked short of taking the transformer out of the case and moving it about 3 feet away =)

    I think its due to poor shielding in the rig. I tend to run mine on external PS and its great.

    Would be interested to know if your noise also goes away on external power.
  6. KN4UD

    KN4UD Ham Member QRZ Page

    The noise is a hiss, with the volume all the way down you can here it. I use head phones about 99% of the time, it is better for me. The head phones make it more noticeable. I can live with it ok. I am not getting a hum like a power supply . It would not be a big deal to build a final audio amp using a lm386 which are pretty clean and no hiss problem it just would have a lower output at the speaker. I am going to take the scope to it this weekend and have a look see where it is for sure. Ordered another QCX today so I need to get the C21 finished and off the bench before the QCX gets here.
  7. KN4UD

    KN4UD Ham Member QRZ Page

    Do you have any hiss with the external supply?
    I know when I opened the case up for the first time my thoughts were this thing is going to have a 60 cycle hum like crazy, with the wires running everywhere I could see no way out of it. I replaced the 14000mf with one you listed here just as a safety precaution . I was surprised that I did not have any hum at all. It does look like to me that some shielding would not hurt or some routing changes. The rig does work pretty good, I am glad I got it.
  8. W4QO

    W4QO Ham Member QRZ Page

    My Century 21 DIGITAL dial won't budge. Pretty sure there is NO string. Have not had it apart. Wonder is anyone has some thoughts, either here or at jim@w4qo.com email.
  9. WU7H

    WU7H Ham Member QRZ Page

    Correct - there is no string. Your PTO needs to be cleaned and re-lubed. Very common issue. Read this: http://www.n5ese.com/c21_pto.htm

    PTO rebuild kits are no longer available, but parts are rarely required. Just take it apart / clean / lube / reassemble. Good luck.
    K7TRF likes this.
  10. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Yup, as WU7H posted above it's a common and well known problem.

    I've re-lubed several Ten Tec PTOs it's pretty easy and well worth the time. Google 'Ten Tec PTO Rebuild' or similar and you'll find lots of instructional articles describing the process but basically it comes down to taking the PTO apart, cleaning off all the old, dried up grease, re-lubing with new grease and putting it all back together. Some folks report having luck with just dripping solvent down the PTO shaft assembly but for a completely stuck PTO assembly I'd do the complete rebuild.

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