Henry 2K-Classic Bleeder resistors

Discussion in 'Amateur Radio Amplifiers' started by W5VQ, Mar 23, 2020.

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  1. W5VQ

    W5VQ Premium Subscriber QRZ Page

    Just spent the last 3 months restoring a 2K-Classic amp, complete power supply re-build. I'm currently testing and the control voltage is correct 12.5VDC, HV on CW 2200/SSB 3500vdc. Everything looks good, but the 4 bleeder resistors seem to run very hot with no load on the plate supply. Using a Fluke laser thermometer in the CW position they read about 225 to 250F, in SSB position 350 to 380F. This just seems too high to me with absolutely no load. The bleeders are 4 - 20K 100 watt wire wound. Anyone know what the normal temp should be? Thanks
    Glenn W5VQ
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    They always ran hot.

    The "console" model 2K/3K amplifiers use a choke-input filter and require a lot of bleeder current to keep the choke properly magnetized. Actually, when you transmit at full power "key down" the resistors get a little bit cooler. They are hottest when "idling" (standby).

    Keep the dust off them so they can breathe a bit and they last a very long time.

    The heat actually isn't excessive: The bleeders dissipate about 153W in "SSB" (3.5kV) and they're rated a total of 400W at 25C. 380F = 193C. The Ohmite 270 series WW ceramic resistors are rated to +350C (derated linearly from full power at 25C to 0 at 350C; so at 193C, the resistor is rated about 52W each x 4 = 208W, So, in operation, in SSB position, they're running at about 74% of their power rating.
     
  3. W5VQ

    W5VQ Premium Subscriber QRZ Page

    Thanks for the info makes me feel better, I got the new resistors from Henry Radio as well as the 16mf oil filled cap and the .1mf 8kv cap for the tuned choke.
    This old amp had a hard life before I got it. The only things usable in the power supply were the choke and the HV/FIL transformer. Been a fun project.
     
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Wow, someone must have beat that poor thing to death.

    The Henry console power supplies were very robust and used within ratings often lasted 50 years. The .1uF capacitor across the choke was a fairly common failure point; I'd usually replace that with a .1uF, 20kV capacitor which is larger but easily fits the available space and used to be commonly available.

    Have fun with the restoration, and get it on the air!:)
     
  5. W5VQ

    W5VQ Premium Subscriber QRZ Page

    Yeah it was near death all right, originally had electrolytic caps someone changed out to a single 8mf 5kv cap. They also completely bypassed the choke and .1mf cap probably because the cap was bad. AND had no bleeders what so ever! I found a doorbell transformer being used for control voltage which was way high. Could go on and on. I'll send you a picture of the power supply the way I got it.
     

    Attached Files:

  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Holy cow.

    With the choke bypassed, the HV should have been way higher (over 5kV), probably enough to start blowing other stuff up. Even the tubes aren't rated for that.
     
  7. W1VT

    W1VT Ham Member QRZ Page

    That is scary!
     
  8. W5VQ

    W5VQ Premium Subscriber QRZ Page

    Yeah, I don't know what the previous owner was thinking. I've checked the RF deck, the Millen HV connector was fried, one disc cap was blown, the DC blocking caps were as soft as bubble gum. Other than a lot of dirt and 25-30 years of cigarette smoke it checked out OK. I think the tubes are the original Eimac's so far so good I let them run all day yesterday with just the filaments on. The cleaning took longer than anything. Here's another picture after cleaning.
     

    Attached Files:

  9. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    "After cleaning" looks very nice!

    I don't believe running the tubes with just the filaments does anything for them; but it might weed out any potential problems with the transformer or connections in that path.

    Hope you measured the filament voltage right at the tube sockets (HV off and disconnected, of course!) because some Henry amps ran them too high (>5.25Vac) which can seriously shorten their life. If those are old, original Eimacs from decades ago, the filament voltage is probably fine but I'd check it.
     
  10. W5VQ

    W5VQ Premium Subscriber QRZ Page

    I have not measured it at the sockets, good advice I will do so.
     

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