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Heathkit HX-10 Marauder question

Discussion in '"Boat Anchor" & Classic Equipment' started by KK6IYM, Jun 18, 2017.

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  1. KK6IYM

    KK6IYM Ham Member QRZ Page

    I am doing the final alignment for the HX 10 Marauder and I have a question. I set the carrier null in SSB using the receiver method and then tried it again with an RF voltmeter at the transmitter output. I get about 5.6 RF volts at the null point. This seems high to me, but only because I compare it to a KWM-2 which calls for less than .2 RF volts. With my wattmeter on the 20 watt scale, it shows less than a watt, so I think I shouldn't be too concerned that it will impact SSB reception at a distance. I know the KWM-2 uses a balanced modulator with 4 diodes and probably has a better filter. I am just not sure what I should expect to see with the HX-10.

    Norm

    [​IMG]

    [​IMG]
     
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  2. K3XR

    K3XR Ham Member QRZ Page

    Can't answer your question Norm but that is one outstanding looking Marauder anything nicer would be new.
     
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  3. AF6LJ

    AF6LJ Premium Subscriber QRZ Page

    This could be due to hum and noise on the output signal..
    Has the transmitter been re capped yet???
     
  4. KK6IYM

    KK6IYM Ham Member QRZ Page

    I have re-capped it and changed some of the critical resistors. It is in beautiful shape, although I did need to clean it up a bit, straighten the case, replace the glass, free up the function switch, that sort of thing. I have come to the conclusion that it had very few hours of use because there is no carbon on the switch contact surfaces. Wiping them with a Q-tip and contact cleaner shows they are perfectly clean.

    In CW, the transmitter puts out over 150 watts. Is this normal? I hate when I get something that seems to over perform expectations. I start to think something is wrong.

    Norm
     
  5. K6GB

    K6GB XML Subscriber QRZ Page

    I don't think mine will ever look that good, still sitting under a towel in the garage.
     
  6. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Back the drive down to keep grid current below 3 mA.

    My Marauder always put out ~100W on CW when operating normally, but I could goose it up by overdriving it and then it would hit >>100W on CW.

    No need to do that, it just shortens the tube life.

    When you see 150W output, what is the grid current?
     
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  7. KK6IYM

    KK6IYM Ham Member QRZ Page

    The meter reads 0 to 1 ma. (I assume you meant .3 ma) The manual suggests 1/2 ma. I have been setting around 1/4 ma and the plate then runs about 220 ma. I may want to just back the drive down to hold the output at 100 watts. All my other transmitters running pairs of 6146's don't put out more than about 110 watts max, but I have no experience with these early Heathkit transmitters.

    Norm
     
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  8. K8ERV

    K8ERV Ham Member QRZ Page

    That was my first SSB rig, but I don't remember much about it.

    TOM K8ERV Montrose Colo
     
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  9. K9STH

    K9STH Ham Member Staff Member QRZ Page

    Several things:

    First of all, the meter has "shunts" which multiply the scale. Therefore, when the meter switch is in the "grid" position, the full scale is 10 mA. Each of the "long" marks, on the meter, represent 2.5 mA and the "short" marks indicate 0.5 mA. Each 6146 tube should never draw more than 3.0 mA which would be indicated by 2-marks past the 2nd "long" mark (in the center) of the meter for the 2-tubes in the final amplifier stage. However, for best tube life, never draw more than 2.5 mA per tube (2nd "long" mark which indicated 5 mA which is 2.5 mA per tube) and running 1.75 mA to 2 mA per tube should result in the longest life of the final amplifier tubes. That means a total of 3.5 mA to 4 mA for the 2-tubes. This would be indicated by the 2nd short mark past the first long mark for 3.5 mA up to the 3rd short mark past the first long mark (2 short marks below the center long mark).

    Next, the wattmeter should not even really "wiggle" when the carrier is suppressed! The specifications for the carrier suppression is 50 dB and 1-watt, at 100-watts output, would be only a 20 dB suppression.

    My HX-10 Marauder is buried beneath several other units waiting to be restored. As such, I have to use the manual instead of looking directly at the transmitter to make comments.

    The earlier versions of the Collins KWM-2, KWM-2A, 32S-1, and 32S-2 all had 2-diodes in the balanced modulator. After a couple of years, the balanced modulator was redesigned to use 4-diodes which allowed for even better carrier suppression. However, with careful alignment all of those units would make the 50 dB carrier suppression specification. As such, the HX-10 should be able to make the 50 dB suppression specification.

    A weakness in all of the Heath SSB transmitters, all the way through the SB-401 and SB-102, is the potentiometer used for the carrier null. With the original potentiometer, it is virtually impossible to get to the "exact" null position and even if this is achieved, the alignment drifts in a very short period of time. The carrier null control needs to be replaced with a 10-turn 200 ohm control. These are inexpensive from sources like Mouser.

    You also need to replace CR-1 and CR-2 with Schottky diodes. Again, these are very inexpensive from sources like Mouser.

    While you are in the area, replace R-6 and R-9, both 330-ohm with 1% tolerance resistors and R-10, a 150-ohm resistor with a 1% tolerance resistor.

    When aligning the carrier null, short both the microphone input (Pin-1) AND the Phone Patch Input to ground. This is to eliminate any hum, etc., from being inserted into the audio circuitry which will make for a carrier if present.

    You have replaced C-5, a 10 mfd 10-volt electrolytic capacitor from Pin-7 of the 6EA8 Speech Amplifier tube, haven't you! If not, immediately replace that capacitor.

    Tighten ALL of the machine screws and nuts that go through the chassis of the transmitter. All of the grounds, in the transmitter, are made through these connectors and they do work loose over the years. Tightening these connectors often "cures" all sorts of "weird" problems as well as eliminating hum in the signal.

    Using the "receiver method" for aligning the carrier null is definitely more accurate than using a meter. One can "hear" the null much more accurately than what a meter will show. I use a receiver for aligning the carrier null for all of the transmitters that I work on for others. Yes, I do have some very sensitive test equipment including r.f. voltmeters that have a full scale reading of 0.001 volts! But, the "ear" method, using a receiver, is easier to do and, in my experience, more accurate than using a meter.

    NEVER run a pair of 6146 tubes at over 100-watts output on 80-meters through 20-meters, over around 90-watts output on 15-meters, and over around 80-watts output on 10-meters. Running more power won't be noticeable to the "other" station but the tubes will definitely know it! Those are the power levels that Collins specified for the KWM-2- series and the 32S- series equipment.

    Anyway, with a little bit of work, the HX-10 should be working to the specifications as published by the Heath Company!

    Glen, K9STH
     
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  10. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    You're interpreting the meter scale wrong. It's actually 0-10 mA, per the manual and also by my experience.

    What you're indicating, if the shunt is still accurate, is 2.5 mA, which actually is about where I always ran mine also. But shunts drift, so it may pay to check that.
     
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