Ten-tec Century 21 restoration

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

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  1. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The pic doesn't reveal so much, but looks like whoever did this was using an external power supply, and not the original internal one.

    I have a C/21 in "original" condition (purchased two years ago, used, from someone who took care of it, and it was perfect) and the only "mod" I made was to step up the output voltage from the internal power supply by a couple of volts, so now it runs about 40-50W output power and nothing else is harmed. The mod involves changing two resistors in the power supply.

    For its simplicity, it's a solid rig. I just used it to make several contacts on 20CW.
  2. KN4UD

    KN4UD Ham Member QRZ Page

    They could have been doing that. I want to put it back to original condition if possible. The gain pot with on and off switch is destroyed, the switch was completely gone. Looks like I will possibly have to use a pot with rotary type on/off switch because I am having no luck finding one. What is you guys input on doing this.
  3. WU7H

    WU7H Ham Member QRZ Page

  4. WU7H

    WU7H Ham Member QRZ Page

    That push/pull switch in my C21 is flakey. I'd just mount a nice toggle on the rear panel, and go with a normal pot.

    For comparison, here is a pic from my C21:

  5. W0GSQ

    W0GSQ Ham Member QRZ Page

  6. KN4UD

    KN4UD Ham Member QRZ Page

    I think I will take your advice and go with a separate switch, would be a lot easier. I have been going by your pictures for reference ever since I took the rig apart . They have been a big help, thanks a lot for sharing them.
  7. WU7H

    WU7H Ham Member QRZ Page

    Glad they are helping. Once you get that C21 working, we can have a C21 to C21 QSO =)
  8. WU7H

    WU7H Ham Member QRZ Page

    Looks like the Ten-Tec wiki has moved, so those links in my old post don't work. Here is the updated link:

  9. KN4UD

    KN4UD Ham Member QRZ Page

    Sounds like a plan to me, we can try it with the QCX too.
  10. W9GB

    W9GB Ham Member QRZ Page

    Replacement parts are available, BUT you have to work like the automotive restorers —
    KNOW distributors, suppliers, AND original mfg. (OEM) of part.

    Ten-Tec Century 21 / Analog : Manual

    START by correctly identifying part needed.

    The POWER ON-OFF switch (S1), is located on the RF GAIN control (part of R1). It is a Push-Pull style switch. In addition to the on-off function, it is used to reset the power supply when it shuts down from an overload. To reset, simply re-cycle the switch, after removing the cause of the overload (usually the DRIVE CONTROL is set too high).

    The RF GAIN control (R1, 1 Kohm, linear taper) is a potentiometer in the receiver antenna line.
    It operates as an attenuator to reduce the susceptibility to overload in the presence of very strong signals.

    CTS in Elkhart, IN was the common “local” supplier to Heathkit and Ten-Tec.
    All major US electronics dustributors carry CTS, like Mouser.

    CTS 450 series, Industrial, 24mm Diameter, 1/2 Watt, Composition Rotary Potentiometer
    Product Data Sheet. There are eight (8) power switch options - rotary and push-pull.
    76196C1B-2E93-4F60-AF4F-78A204AC951F.jpeg BF50A773-B1DC-4314-8A49-E521BF0FE421.png
    CTS potentiometer, model 450 with DPDT switch, and SPST switch.

    The Music Industry uses this part in countless music equipment (guitar amps, etc.) —
    HOWEVER they commonly use potentiometer values from 100 Kohm to 500 Kohm for their vacuum tube equipment.
    Hacking the Push-Pull switch potentiometers

    Amateur Radio Equipment traditionally uses 1K ohm and 10K ohm values,
    with Linear or Audio tapers.

    On identical control models (450 series), you can place a “new switch assemble” on the old potentiometer — IF the original resistive control is good. You basically become the CTS Repair technician, re-assembling how they assemble these at factory (special orders).

    I have performed this repair since 1970s on home stereo restoration and older anateur gear —
    after a few EEs, with just lab bench experience, wrecked the stereo gear trying to find why power was absent.

    Last edited: May 7, 2018

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