A remote Power Supply for the SB-220

Discussion in 'Amateur Radio Amplifiers' started by WA6MHZ, Apr 26, 2017.

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  1. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    OK I started the thread early
    The scope of the project is to physically remove the ridiculously heavy transformer from the Heathkit SB-220 and mount it on a separate chassis about 6 feet away.
    This will involve routing the High Voltage over that distance, along with the AC wiring and other wires required. A 3rd unit will be mounted at the operating level to remotely turn on power, standby and key the amp.

    This will be a 6 Meter only amp and it will sit on a HIGH SHELF a long ways from the rest of the station, as there is no room nearby for the amp to be placed. The only parts in the amp will be the Tuned circuits, tubes/sockets and the filament transformer. This should make it only 10 pounds or less. ( I don't know how heavy the filament transformer is)

    Since this is 6 meters only and the primary operation will be SSB (maybe some CW) in the 50.125 portion of the band, no retuning should be neccesary for short QSY excursions. The input and Pi Network will be set and forget. I wont need to switch the meters as I will have a Dual needle wattmeter on the output externally, so maybe I will just leave it on Grid Current.

    I will drive it with a solid state amp as my FT-736R is only 10W and I need 100 W or drive.

    So I am in the collecting data stage at this point. I will be picking up a SB-221 Saturday to begin the mods on. I had hoped to find a CHICKENBANDERIZED Amp brutalized, but this one is in excellent condition. I will save all the HF circuitry for restoration someday for HF if neccessay.

    Since a completely new power supply will be built, the only HEATHKIT PS component to be kept is the Transformer.

    One of the first items that needs to be acquired is the materials for the HV cable. I need atleast 6 feet of 10KV cable and the Millen High Voltage connectors.
    Here is a place that has them, but they are MIGHTY PROUD of them!!!
    YIKES!!! $40 for 2 pair of connectors!! this is going to be an EXPENSIVE project!!!
    I will be CAREFULLY COMBING the TRW Swapmeet for these , looking in boxes of junk.
    Somewhere I have some of these, not that I can ever find them. they are buried in a 1000 pounds of debris. Need to score the HV cable too. Spark plug cable probably won't do.

    Of course the amp will all QSK'd andwith a soft start (though I am not sure if that is for the filament or HV transfomer) investigation to follow. Maybe its for both.
    OK this is just the Openning post, much more follow.
  2. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

  3. K5RT

    K5RT Ham Member QRZ Page

    Pat, years ago when I was a struggling college student, I used the center conductor and dialectic (removed the braid and vinyl jacket) from RG-213 to feed 3 kv to my home brew 4-400s. IIRC, the dielectric is rated at 3700 volts or so. It's not the most flexible stuff to use, but it worked in a pinch.

    I've seen guys use a PL259 and chassis mount SO-239 for HV connectors. But I wouldn't do that #%*$ if I was you

  4. WA7PRC

    WA7PRC Ham Member QRZ Page

    RG-213 is indeed rated 3700 VRMS (datasheet). However, it's best to use components rated and intended for a given use. Lots of folks use RG-coaxial cable but, there's other cable intended for HV. I bought some smaller OD triaxial stuff rated 5KV for about a buck/foot. Unlike RG-213 (7 strand center conductor), it has 19 strands, and is quite flexible. :)

    Millen HV connectors are problematic; the potential for shock (or worse) exists. There are many other connectors also intended for HT use. I really like the SHV (Safety High Voltage) series because they're a coaxial twist-lock connector that first engages ground before the center conductor. The problem is, they're not at all inexpensive.
    WW1WW likes this.
  5. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    Here is a very poor drawing of how the sturdy Remote Power supply chassis will be made. It is all from Home Depot angle aluminun and bars. About 1/8 inch thickness so once assembled One could stand on it. So it will easily handle the 100 lb transformer!! 20170426_060545[1].jpg
    Yes i know I get an F in drafting but I just wanted to conceptualize the process. The transformer sits mid deck. I will put more aluminum bars under the transformer mounting plates to support it in the center. This is a very complicated assembly and probably the most difficult process of the whole project. There is no room for error. Each piece has to be PRECISELY cut and fit. 8 vertical bars have to be within a Millimeter of each other to fit on the angle pieces. The 4 angle pieces all have to be incredibly precise. Then the are the 4 end angle pieces. These are cut with a Harbor freight cutoff saw and then filed to fit perfectly. Then the piece are drilled and tapped for the mounting hardware. the holes are countersunk as outer panels are placed over the inner frame. I used the same process in building the HP-240 and it came out great, but was a tremendous amount of work. No standard aluminum box would support the weight of the transformer!! Home Depot will LOVE me after I come in to collect all the metal. Then I need to find sheet aluminum for the side, front and rear and bottom panels. Perforated aluminum is used for the top and sides above the lower chassis.
    Heavy duty handles are attached to the 2 ends to enable carrying the Power Supply into place.
    here are some pix of the HP240
    IMG_0310a.jpg IMG_0336a.jpg
    PHEW!!! I am already tired thinking about how much work it will be. But once completed, it will be MAGNIFICENT
    Last edited: Apr 26, 2017
    N4ZAW likes this.
  6. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    More HP240 Pix
    The REMOTE SB221 PS will just be a bigger version of this!!!
    KE5OFJ and N4ZAW like this.
  7. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    I need to find more of this Perfboard. I don't believe there will be a problem with high voltage breakdown, as there was no problem on the HP-240. usually when Perfboard gets carbonized from burning that resistance occurs. The Perfboard should have no problems at high voltage.
    I need Radio Shack to reappear as there is no other source for this perfboard. I have scoured Ebay and Amazon! More things to buy at TRW!!
  8. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    What size of board do you need? 0.1" hole spacing? I've got a pretty big stash of this and will gladly donate some.
  9. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    Another added mod for the HP240 will be 220VAC operation on the SB-221REMPS.
    OK that is the new Project designator
    for 220VAC operation, just like in the Heathkit, jumpers will need to be changed to select that operation. I don't wanna put a switch in, as it might be inadvertantly set to the wrong position!! But if U hafta change jumpers, that is a very forward operation requiring extra effort to accomplish. Initially it will be set to 120VAC in as I have no 220VAC into my shack. I run my Drake L7 on 120VAC just fine and never (KNOCK ON WOOD) have blown the breaker. I really climb into the mic too during pileups and run the full gallon on RTTY and CW!!!
    Another feature to be added not seen in the HP-240 is the use of a CONTACTOR for AC enabling. The PS will be only running on 12V standby power until the remote control requests power. at that point the contactor will kick in sending 120/220 to the PS.

    One other head scratcher is the resistors to use for 120 or 220 in the soft start circuit. Harbach has U use 10 ohms for 120VAC and then 20 ohms for 220VAC.
    so maybe I will use 15 ohms to split the difference.

    Another area of question is WHERE to put the Soft Start. Some articles I have read says the Soft start is for the FILAMENT Transformer as the tubes need soft starting. Other articles say it is the Plate Voltage Xfmr. In the SB-200, both were inside one transformer so it wasn't an issue.
    If it is for the FILAMENT transformer, then I will put the Soft start module in the SB-221 chassis. Otherwise it goes in the SB221REMPS.
  10. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    Not quite sure yet. Thanks so much!!! Yes .1" is perfect. The radio shack boards were about 6" by 6". I need to get the transformer hole spacing dimensions before i start to build the chassis. The perfboard will go on both sides of the transformer. one side for the caps and the 2nd side for other circuitry. Like the Bias supply and 12V and 26V PS components. The contactor will take up alotta space under the chassis, I saw one at Murphys, and it is about 3" by 3" So this chassis is going to be almost twice the size of the HP-240!

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