TS-2000 drivers - from 2SC1972 to RD15HVF1

Discussion in 'Radio Circuits, Repair & Performance' started by CIPMAN, Mar 30, 2020.

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  1. CIPMAN

    CIPMAN QRZ Member

    I have a TS-2000 bought in 2001 which I used till 2005. At that time I switched ham radio to sports as I was starting to gain weight. So my working TS-2000 went in a hard case in a closet where it sat quitely till the present days. Since I'm stuck at home, I tought it would be nice to get back to ham radio so I took the rig out.

    After a brief test: no TX power on HF and 144. Searched around, most likely the 2SC1972 drivers are shot.
    Took out the pre-driver (2SC1971) as well and tested them: pre-driver is ok ( https://i.imgur.com/yWcsq1e.jpg ) but drivers 'evolved' into resistors ( https://i.imgur.com/s6rYAIN.jpg )

    Since 2SC1972 transistors are not available anymore, I'm considering replacing them with a pair of RD15HVF1 mosfets, modifing the circuit a bit to match the ICOM IC-756PRO III schematics which also used to use 2SC1971 as a single ended pre-driver.

    Has anybody here done that? I've found a pic on a russian site with the mod done 10 years ago but not many details were givven.

    73's de Cip
     
  2. WA4SIX

    WA4SIX Ham Member QRZ Page

    You may want to check some older CBs. They uses 1969s & 1972s for final amps. Any time you find an up to late 90s CB at a yard sale for $5, get it & pillage the rare parts.

    Ed
     
  3. CIPMAN

    CIPMAN QRZ Member

    Thank you. That's a good idea if you can find the said CB radios. I just searched, no luck. Not to mention yard sales these days are out of question.

    My understanding is these transistors were badly designed and/or manufactured from the first place. They get shot not only in Kenwood's or Icoms Pro II's, but in CB radios as well. Even if I find a NOS 2SC1972 pair there's a big change they will soon fail. Someone here reported 4 years ago using a 'new' pair of 2SC1972 and they worked only some 30 minutes.

    One option in the US would be a direct replacement NTE343 ($50/pcs on amazon these days). But these transistors must be matched (don't think the amazon supplier can send a matched pair) and I consider them to be too expensive (including shipping and taxes to my place) compared to the current value of my rig.
    The RD15HVF1 is about $10/pcs and it's bomb proof (with proper care when soldering - grounded hands/tools and soldering iron) and they can be found mostly all over the world.
     
  4. G4COE

    G4COE Ham Member QRZ Page

    Remember-:
    When replacing these 2SC1972/1971 transistors with any other NPN types such as CB PA transistors the majority have collector tab and middle lead in the middle 2SC1969.... and so on.

    2SC1971/1972 have their tab connected to the emitter which is the middle pin.

    There is one caveat:
    2SC1971/1972 will work at 145Mhz, the driver in the TS2000 is the VHF take off point, replacing these with CB transistor will result in losing VHF, needless to say these are the VHF driver as well.

    Edit:
    Note the single ended driver has a emitter resistor meaning that a insulating mica is required, without this the emitter resistor will be shorted out and the driver stage *may* oscillate and create thermal run-away.

    Dave
     
    Last edited: Mar 30, 2020
  5. CIPMAN

    CIPMAN QRZ Member

    Using the factory transistors is bad enough, using other BJTs not 100% compatible just doesn't worth the trouble IMO.

    Now that you mentioned the single ended 2SC1971 pre-driver, I'm in the process of scratching my head as I can't figure out how it was installed. It had an insulating bush but no mica or any other kind of thermal pad/insulation underneath.
    I ordered some mica TO220 pads and probably use a bit of thermal paste as well.
    The drivers are grounded, the intended mosfets replacement as well, so no worries here.
     
  6. G4COE

    G4COE Ham Member QRZ Page

    Make sure Q2 2SC1971 driver does have a emitter resistor, R14, 2.2R decouple by a C20 330pF, without any insulation R14 and C20 will be shorted out, this will increase the current through the transistor, increase the gain and cause stability issues with thermal run-away.

    Sometimes the mica is difficult to see once the transistor is removed. Might be an idea to have a look at the TS2000E that uses FETs in place of 2SC1971/1972.

    Dave
     
  7. CIPMAN

    CIPMAN QRZ Member

    Spot on Dave, the mica insulator was in place, on the chassis! I cleaned the seatings without lifting the pcb, there was no paste slipped under the mica so it was hard to see. Now I used a flash light from an angle to see if it shines differently. Cheers for that! Here it is on the toothpick https://i.imgur.com/UDfWdGG.jpg :)))

    I didn't lift the pcb so I measured R2 paralleled with C20 (they're on the back side of the pcb): multimeter shows 2.2R, a multifunction tester and a swr meter show the same thing as a separate 2.2R/330pF parallel circuit so all should be ok.

    Yes, I had a look at the schematics of the newer TS2k version with the FET's but it looked more complicated to adapt. At the moment I'm willing to try changing to RD15's. Already ordered the parts this evening, they should arrive in 2-3 days.

    Here's both schematics side by side, 756PRO3 on the left, TS-2000 on the right: https://i.imgur.com/o7livg2.png
    I'll get back with the new schematics I want to try, for the moment it's only in my head.

    Thank you,
    Cip
     
  8. G4COE

    G4COE Ham Member QRZ Page

    I've had that problem with the mica being well and truly stuck.... I'd have left it intact, the first time I was fooled too.

    If you look back in this section there should be a couple of threads on replacing those transistors in the T2000, they are used in other rigs as well, I think one guy replaced them with 2SC1969's, worth doing a search on this board, doing this would lose 2mtrs because the ft are only 30Mhz.

    Dave
     
  9. CIPMAN

    CIPMAN QRZ Member

    Thanks, I searched and browsed this forum up and down but I'll search some more. Losing a band or more is not appealing to me.

    All right, here's the schematics with the modification I'm planning to make: https://i.imgur.com/ZCUFaaP.jpg

    Couldn't find the double diodes (DAN202U) at my usual suppliers and I'm not going to order them from the big guys. I've seen the russians used a single 1N4148 in the 756PRO2 to PRO3 conversion and an unknowk but look alike diode in the TS-2000 conversion. So this is what I'm planning to use for now.

    Another thing I'm not sure is about C26 + C27. They were missing in the picture of the converted TS-2000. Honestly, I don't have a clue what they do there (filter harmonics over VHF?).
    Same thing about R24 which is on the other side of the PCB. Don't know if it needs to be taken out (hopefully not).
     
  10. CIPMAN

    CIPMAN QRZ Member

    Mission accomplished!
    It took a while as the first RD15HVF1 pair was a fake and the second pair took 3 weeks on the road (normally 7 days or less).

    Final version of the schematics (lowered a resistor a bit):
    [​IMG]

    Picture of the [not that pretty] result:
    [​IMG]

    Output power test (+100W cw on 20m):


    Automatic antenna tuner seems to be working fine.
     

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