SP-600 drift

Discussion in '"Boat Anchor" & Classic Equipment' started by K6BSU, Jun 2, 2019.

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  1. K6BSU

    K6BSU Ham Member QRZ Page

    I searched the forum but couldn't find an answer to SP-600 drift. I seem to remember a recommendation to replace the 6C4 HFO with some other triode. What could that be?
  2. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    To correct this problem, Hammarlund came up with the JX- series and crystal control.

    Although I never tried this, and at one time I did own 2-each SP-600-JX-17 receivers, there are supposedly several capacitors, in the tunable oscillator circuitry, that can be replaced with specific temperature compensating types.

    All of the SP-600 receivers that I have ever seen are especially drifty above around 10 MHz. Below 10 MHz, it "depends" on the individual receiver.

    Glen, K9STH
    K0UO likes this.
  3. K4RT

    K4RT Ham Member QRZ Page

  4. W9GB

    W9GB Ham Member QRZ Page

    Last edited: Jun 3, 2019
    K0UO likes this.
  5. K6BSU

    K6BSU Ham Member QRZ Page

    I don't notice any drift on my SP=600. I sometimes listen on 20M, and it stays on freq (I think)... tuning is so quick that it's hard to get right on a SSB signal. I end up tweaking with the BFO for "good" sound.

    I used the 600 in the USAF (Intercept Radio Op), but my monitoring assignments were rarely above 6 MHz or so. Also, the transmitting stns tended to drift around a lot, so it was hard to know who was doing the drifting!
  6. W7ANM

    W7ANM Ham Member QRZ Page


    I have an HQ-150 that I have had for years and it has been fairly stable for this type of receiver. Lately it started to drift more and more even after being on for hours. I remembered my R-390A having a drift develop (they don't drift) and cured that with a different PTO tube. It is recommended to use a tube with some hours on it as a new one can be a little drifty due to break in issues. So back to the Hammarlund HQ-150.... I replaced the 6C4 in it and pretty much no more drift after an hour or so warm up.

    I would recommend getting a few used 6C4s and trying them for one with the least drift in your SP-600. They don't have to have new emission to work in this application. In fact for my HQ-150 fix I used the poorest emission 6C4 I had in my stash.

    Hope this helps.
  7. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page


    The problem with the 6C4 as the local oscillator is very common especially in the Hammarlund series receivers. It is not uncommon for a brand new 6C4 not to work at all or, at least, stop working on the higher frequency bands.

    The HQ-150 was the last of the Hammarlund series that started with, at least, the HQ-120X, then the HQ-129X, followed by the HQ-140X, and, finally, the HQ-150. After a fairly short period of time, the stability is excellent. Unfortunately, this is generally not true of the other Hammarlund receivers including the Super Pro series especially on the higher frequency bands. Those receivers can often be stabilized but only with some work.

    Back in the mid-1960s, I used my original HQ-140X, along with a W2JAV terminal unit, to copy RTTY transmitted on the old Reuters New York to Havana link. After less than 30-minutes warm up, the HQ-140X was very stable. I could walk away and come back hours later with page, after page, after page, of perfect copy. It definitely took a very stable receiver to do this. Usually, at both ends, a crystal controlled receiver was used like the SP-600 JX- series.

    Glen, K9STH
  8. K4RT

    K4RT Ham Member QRZ Page


    I'm confused Does your SP-600 drift or doesn't it? Does it not drift just on 20m?
  9. K6BSU

    K6BSU Ham Member QRZ Page

    Of course my SP600 has some drift at 14 MHz. All analog HF oscillators will drift somewhat. What I tried to say is, the very slight drift is easily corrected using the BFO control. The main tuning control is too sensitive to use it for correcting some drift.
  10. K4RT

    K4RT Ham Member QRZ Page

    Understood. Yes, my SP-600 is the same. I really enjoy this receiver.
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