Heathkit HDP-121 PTT switch location

Discussion in 'Microphones, Speakers & Audio Processing' started by KC1BMD, Nov 24, 2017.

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  1. KC1BMD

    KC1BMD Premium Subscriber QRZ Page

    I have seen some Heathkit HDP-121 mics sold that don't quite look the same. Some might be HDP-121A or maybe standard EV mics (not the ones sold through Heathkit). Some have the PTT switch on the base and some have it located on the vertical shaft.

    Q: Does anyone know if the switch can be relocated from either position to the other? I saw a reference in EV doc (not Heathkit doc) to their EV-719 mic about doing just that but not sure if it was limited to that mic or possible with all similar EV and Heathkit(EV) mics.

    Below a pic of the HDP-121 in question. Can the switch be moved from vertical to base (also swapping the Heathkit label)?
    1345478.jpg
     
  2. W0GSQ

    W0GSQ Ham Member QRZ Page

    Yes, the plastic filler piece with the Heathkit name on it snaps out, I moved mine in 1979 when it was new.
     
  3. KC1BMD

    KC1BMD Premium Subscriber QRZ Page

    So there is enough wire length to extend the switch from the vertical to the base with no splicing? Is the switch mounted to the button and moved all together as a single assembly? On a difficulty scale of 1 (extremely easy) to 10 (extremely difficult), how would you rate it?

    The HDP-121 uses a "dynamic" element, although supposedly Hi-Z (~20KOhms from my research). Does anyone know if this mic would be suitable for the SB-101/SB-102 tube transceivers or whether it was intended for use with Heathkit's later SB-104/104A solid state designs?
     
    Last edited: Nov 25, 2017
  4. W0GSQ

    W0GSQ Ham Member QRZ Page

    It's a 1. Take the bottom cover off and take a peek.
     
  5. KC1BMD

    KC1BMD Premium Subscriber QRZ Page

    Thanks. I would take a peak but I have not purchased it yet. Any clue about the suitability for the SB-101/102?
     
  6. W0GSQ

    W0GSQ Ham Member QRZ Page

    Hi-Z mic works well with tube gear.
     
  7. W9GB

    W9GB Ham Member QRZ Page

    YES, the Switch can be relocated.
    The original Electro-Voice datasheet (EV-619KK) — 4 pages —
    has the instructions to move the PTT switch assembly.
    http://www.pestingers.net/pdfs/other-radios/microphones/ev-619.pdf

    Heath Kit 1970s microphone usage:

    The Desk Microphone HDP-21A came on the market in 1968. It was really an Electro-Voice 638.
    It was the successor of the HDP-21 (Electro-Voice 605) that came on the market in 1962.
    The HPD-21A was then replaced in 1976 by HDP-121 (Electro-Voice 619) and by the HDP-121A (Electro-Voice 620) in 1978. It is a Hi-Z dynamic microphone with crystal clear audio.
     
    Last edited: Nov 25, 2017
    W0GSQ likes this.
  8. KC1BMD

    KC1BMD Premium Subscriber QRZ Page

    Thanks. It also looks like the Hi-Z version has a tiny box in the audio line at the mic, which I'm guessing is a matching transformer (to better match the dynamic mic to the Hi-Z input of the Heathkit rigs of the day). The link shows the document for the EV-619, not the EV-619"KK" version, which I think differed somehow with the switch contacts.
     
  9. W9GB

    W9GB Ham Member QRZ Page

    Leaf switches (PTT) used by Electro-Voice and Shure can be damaged.
    Restoration of those switches possible with parts from Switchcraft (current and surplus discontinued parts).
     
  10. K7BGV

    K7BGV Ham Member QRZ Page

    I recently acquired an EV-638 HI Z mic to use it with my HW-101.Does anyone know what would be the approximate output,( mV level )out of this mic? I crank the mic volume all the way up and it’s kinnda weak.I’ve checked its impedance and it measures about 21.7K at 1 khz. 20.0 k at 100Hz and 28.9k at 10khz which seems to be correct...
    Vic
     

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