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Simple Heathkit DX60B Question

Discussion in '"Boat Anchor" & Classic Equipment' started by KN4SMF, Jul 1, 2021.

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  1. KN4SMF

    KN4SMF Ham Member QRZ Page

    I am presently considering the purchase of a DX60B transmitter. I like restoring rigs. But before I go any further, does this model suffer or exhibit the under-powered power transformer burnout issue I heard so much of in the 40 and 20 models? Thank you.
     
  2. W7UUU

    W7UUU Principal Moderator Lifetime Member 133 Administrator Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    Nope. The DX-60 and DX-60b are solid as rocks - not under-powered at all as their predecessors were.

    Go for it! It's a GREAT old transmitter!

    Dave
    W7UUU
     
    K1OIK likes this.
  3. KN4SMF

    KN4SMF Ham Member QRZ Page

    Thank you for the quick answer. I am awaiting the return of the owner so I can see if I can snag it. Now I have another question which is a complete sidetrack of the thread title. But I see no point in continually starting new threads. I once saw an old Eico tube transmitter, but forgot the model. It was a screen modulated job probably not too much different from this one. And it had a dedicated external plate modulation amplifier that could be used with it, as well as a dedicated VFO. Looked like a neat rig. One thing I noticed was that the external plate modulation amplifier looked almost exactly like a regular audio amplifier. I'm sure it's different from an audio amp, but my question is, how much different? What does the plate modulation amp have that a regular audio amp doesn't have? Maybe you can see where I'm going with the question.
     
  4. N2EY

    N2EY XML Subscriber QRZ Page

    The transmitter you are thinking of is almost certainly the Eico 720.

    https://people.ohio.edu/postr/bapix/Eico720.htm

    The manual can be found here:

    http://bama.edebris.com/download/eico/720/EICO 720 Instruction.pdf

    It is NOT screen modulated; it's CW only. Eico didn't make any screen-modulated transmitters.

    To put a 720 on AM requires an external modulator. The Eico 730 was made for this purpose:

    https://people.ohio.edu/postr/bapix/Eico730.htm

    The manual is here:

    http://bama.edebris.com/download/eico/730/EICO 730 Instruction.pdf

    The matching VFO is the 722:

    http://bama.edebris.com/download/eico/722/EICO 722 Instruction.pdf

    Download the manuals and study them; there's a lot of info.

    The Eico looks a bit like a hi-fi amplifier of the era, because Eico made them too. It even used tubes commonly used in hi-fi amplifiers of the time, such as the 12AX7, 6AN8, EL34/6CA7 and the GZ34/5AR4. They were common and inexpensive then, but it's not 1960 any more.

    Some significant differences between modulators and hi-fi audio amplifiers:

    - Modulators for amateur use are generally designed for high impedance microphone input. Some have an additional high-level input as well.
    - Modulators for amateur use have output transformers designed to work into a high-impedance load (several thousand ohms) rather than a speaker voice coil of 4, 8 or 16 ohms
    - Modulators for amateur use have output transformers designed to work with significant DC current flowing in the secondary, without saturating.
    - Modulators for amateur use are usually not "high fidelity", but rather "voice communication quality". The frequency response is restricted to the speaking voice range (300 to 3000 Hz or thereabouts) and there's often a clipper, compressor or other means of reducing the dynamic range. The Williamson and Ultra-Linear circuits are generally not used in modulators.

    There are several ARRL Handbooks and other publications on various sites, free for the download, which can answer many of your questions. Check you PMs ("conversations") for more information.

    73 de Jim, N2EY
     
  5. KN4SMF

    KN4SMF Ham Member QRZ Page

    Thank you. I was born at the wrong time. I love the tube rigs and I hate SSB. I can hear the SSB guys just fine on my Hallicrafters SX-16,or HQ-170, but it takes work. They have these fancy rice rigs they don't have to know anything about, and they can just tune to whatever their digital readout says. AM is beautiful. You tune in and see that S meter fly over to a nice strong signal, and hear a full beautiful sound spectrum. It knocks all that SSB noise out. SSB is just awful in comparison.
    My Dad was a golfer. I hate golf. But he didn't just go out and buy a good golf score by buying new clubs and balls. He did it with whatever club and ball was in his hand at the time. I compare that to radio. CW and AM takes skill and learning. SSB is simply spending money for a fancy rice rig. It's just not the same at all.
    I'll get this figured out.
     
    WN1MB likes this.
  6. W3SLK

    W3SLK Ham Member QRZ Page

    If you have an opportunity to purchase an Eico 720, do it! I have 2 of them and they very versatile units. So if you get that DX-60 rig or any other rig that has no imboard modulator you can use it up to 100 watts of carrier, as long as the tuning capacitor is rated for 4X the voltage. The modulation transformer has a multi-tap so it can be configured for different impedances. I use one of mine with an old Stancor 202 transmitter.
     
  7. K5DH

    K5DH Ham Member QRZ Page

    The DX-60 series rigs often suffer from failures of the Function switch. They use contacts on the Function switch to make/break the HV circuit in the PS. I have a friend who's dealing with that issue right now, and I experienced it myself with a DX-60A back in the late 1970s. Other than that weakness, the DX-60 series are good, solid rigs. It's rare to hear of a power transformer failure (unlike the DX-20/35/40 series, whose transformers fail a lot).

    The Eico 720 is a good, solid CW rig and they can still be bought at reasonable prices. Expect to pay "out the wazoo" for the 730 modulator and 722 VFO, though. They're scarce and in demand, and sale prices reflect this. Last year, I sold a really nice 722 VFO for $200 plus shipping. It was "collector grade", the nicest one I've seen in decades. A couple of months ago, I sold a terribly ugly, rusty, hacked up, barn-find (but it worked fine) 722 for $50 plus shipping. Compare that to a Heath VFO, where $50 - $75 will get you a nice one.
     
    W1BR likes this.
  8. KN4SMF

    KN4SMF Ham Member QRZ Page

    Why do the companies do these things? A wafer switch is not something you're suppose to use to switch a high voltage. I can just imagine the arcing continually hammering those little bitty contacts. I just finished a job on a Knight T-60 that had 2 melted wafer switch contacts. I had to remove the entire assembly, take it apart, file off the rivets of the 2 contacts, and find a junk wafer switch to steal contacts from, and use itty bitty screws and nuts to put them in the wafer. The job turned out and the transmitter worked. But in the meantime I got to see first hand and appreciate the tiny surface area of electrical contact between the switch contacts and the flat that turns around against it. I concluded wafer switches are just not something designed to carry a lot of voltage or current. But I suppose that's the difference between these hobby/consumer grade pieces of gear and military/commercial gear. Maybe some day I will manage to snag a Collins ART-13 or the like. I bet the corporate bean counters didn't scrimp on the engineers who designed those rigs.
     
  9. W0GSQ

    W0GSQ Ham Member QRZ Page

    The customer for the ART-13 was willing to buy equipment at a slightly higher price point.
     
    WN1MB likes this.
  10. WN1MB

    WN1MB Ham Member QRZ Page

    Search the Web - I recall several modifications that address that issue with the DX-60. It involves changing the function switch wiring so it's switching power to an added relay (with beefier contacts) to do the HV chores.

    Other than that issue, a very good transmitter. With some minor component changes in the audio stages, they can be made to sound amazingly good. If memory serves, WA1HLR documented both the PTT and audio enhancement mods. Again - search the Web.
     
    KP4SX likes this.

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