Discussion in 'Amateur Radio Amplifiers' started by WA6MHZ, Jan 11, 2019.

ad: L-HROutlet
ad: l-rl
ad: Left-2
ad: abrind-2
ad: Left-3
ad: L-MFJ
ad: Subscribe
  1. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    Ok now I REALLY have a Project!!

    A long time very good friend donated a once working 4CX250 amp with PS right around Christmas!!

    What a WONDERFUL GIFT!!!

    Here are the initial pix
    and the Matching Power Supply

    I was just TICKLED and loaded it in the back of the SUPERFLEX, I got the amp in the house and upstairs, but the PS would remain there until SUE AF6LJ came over and unloaded it.
    This is ridiculously heavy! making a SB-220 look like a FEATHER!!!

    As we can see, it is a PLUMBERS DELIGHT from the 1972 ARRL VHF Manual.

    the blower mounts on the side plate which is a problem for mounting in a cabinet

    So once Sue got the PS out of the SUV, we cut the wires and removed the transformer so that the 2 could be moved upstairs to work on.

    Previously, the Test room was shared with the radio shack, but that proved to be usless as all the junk was piled up blocking the test equipment. Now it is all upstairs neat and ready to work with.

    So after visually inspecting all this, here is what I have found:

    1) Built by an unknown person sometime maybe in the 70s or 80s. IT worked until the screen supply burned up and a repair was made that was unsuccesful

    2) Power Supply is a full wave bridge with 6 MONSTER 2100uf at 400VDC caps!!

    3) I have a WHOLE BOX FULL of 4CX250Bs, but this uses 4CX250Fs which are 26V Fillaments!!

    4) Of course now it has become a CAT RANCH ELECTRONICS project and QRZed knows all too well what that means!!
    WA9UAA and KA0HCP like this.
  2. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    What is unknown is what the story on the Screen supply is. This design uses big Zener diodes with volage coming from the HV Chain, 2nd Cap from bottom.

    we measured the transformer at it will put out around 1800VAC at 120VAC in.
    Who knows where the transformer was from? But it is a really nice Hypersil which is very expensive!

    And Not sure I would want to have to buy 6 more of those caps!!! Might cost me $100 each!!

    We got the transformer up to the test lab and it will stay on the floor for quite awhile! No way I can muscle around this PS with the transformer installed!
  3. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    I have long needed a 2 Meter Killerwatt!! Someday I need to get the long john M2 2M DX beam up too!

    One very important issue is the SAFETY OF THE CATS!!!! Theses Pusses like to noze around and we don't want these kitties to be VAPORIZED by Electricity! So I need to make some sort of protection enclosure to keep UNAUTHORIZED CATS OUT!

    The RF Section looks Pristine. But the availabilty of 4CX250Fs are a real issue. That is what you need to search Swapmeets for! (That's where I got all the 4CX250Bs!)

    Next issue is what to do about the Screen Supply. Sue says to forget the Zeners and use an OA2/OB2s combo.
    that would be a good idea if I can find a place to squeeze those.

    the mode of Failure was the burning of wo 75k 40W resistors.

    The worrry I have is that the special Screen bypass caps in a socket are bad. An ohms check showed no problem at them, but it is unknown if they breakdown at high voltage (350V Screen)
  4. N2EY

    N2EY XML Subscriber QRZ Page

    In QST for February, 1964, there is a project by W1HDQ for 6 and 2 meter kilowatt DC input amplifiers using 4CX250Rs. Lots of information there about tube choice, control and metering circuits, screen supply, operation in Class C CW, Class C plate-modulated AM, Class AB SSB linear and even Class AB AM linear.
  5. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    OK time for the QRZeders to chime in. DO I need all those UFs? SB220 types use 200ufs each but this is 10 times that!!!

    One thing it doesn't have is a FILAMENT TiMER LOCKOUT! I will install that in the CAT RANCH ELECTRONICS upgrade!

    So when a repair is made to a unit, it has to be determine WHY IT FAILED! Is the fault still in the unit? Is one of the tubes blown? Won't know till I plug it in. If it blows up again, then I guess a tube or the socket is bad!

    Another option is to yank out and toss the 4CX250Fs and find a 6VAC @ 6 amp filament transformer. then use the ordinary 4CX250Bs!

    Penelope (and Phoebe) are making suggestions. And so is Sue AF6LJ

    some decisions will be made by me! Money will be a great issue! Im on Social Security!
    WQ4G, K9ASE and KA0HCP like this.
  6. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Hi to Sue for me!

    If' you have a bag full of 250B's this sounds like good sense to me.

    After close visual and repairs, I'd consider testing the frame out for problems holding voltage, etc. before putting tubes in it.

    Sounds like a fun Cat Ranch Extravaganza.
    KD0CAC and K9ASE like this.
  7. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Cat Ranch rides again! Wooohooo!!!

    p.s. *Waves at Sue!*
    K9ASE and KD2ACO like this.
  8. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    If I DO decide to convert it for the Bs, I found a transformer at RF Parts which might work
    it is 12.6V Center tapped at 8A. the 250Bs would only draw 6A. the Center tap could be grounded and each leg of the secondary ran to the Heater hot pin.
    But RF Parts is reallt proud of it! $47!!!
  9. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    Sue and I have extensive disagreements on this! I say that the HV section is probably good to go and the existing caps are still good. She wants them all replaced! HEY!!!! Whose wallet is being used here?
  10. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    The RF parts transformer has 4 inch mounting holes. Umm the chassis is only 3 inches high!!! Back panel real estate is well spoken for!

Share This Page

ad: elecraft