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hallicrafters SR-2000 time delay relay?

Discussion in '"Boat Anchor" & Classic Equipment' started by WA6MHZ, May 20, 2013.

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  1. WA6MHZ

    WA6MHZ Subscriber QRZ Page

    Another long hard day over the SR-2000, and I am about where I was when I last left off.

    I looked at the IF Transformers, and even took them out. I noticed someone had installed an 18pF cap across the output, which isn't shown in the schematic. I also physically removed the transformer and thoroughly inspected it. Everything looks well and unmolested. I put it back in WITHOUT the 18pF and now, I can tune both slugs. Now, the transformers are NOT broadbanded like Jim recommends, but they are peaked to pass maximum signal. And it does work well on RX. On 40-10M, I can hear signals down BELOW -117dBM. WOW!!! That is INCREDIBLY Sensitive! SO that says everything in the IF path HAS to work, as the same circuit is used on TX and RX. SO the problem is elsewhere. 75M is a little numb though...

    It MAY be a problem with the bandswitch. I can see just a LITTLE signal going into the Driver but nothing whatsoever coming out. All voltages look fine. So it could be a coil issue with the bandswitch not making correct contact.

    HAIR TEARER!!!

    My mind is just NUMB from trying SO HARD all day long to fix this radio. Not getting anywhere. But it DOES make a good RECEIVER!!!
     
  2. K9AXN

    K9AXN Premium Subscriber QRZ Page

    Hi Pat:

    The 18 pf cap is C37 and is across the secondary of T1. In the SR-2000 it is on the transformer and the SR-400 on pin 2 of V3.

    The receiver when working properly will have a 3db MDS of -138db --- much more sensitive than necessary.

    Reinstall the cap if it is C37 and realign the 1st I.F. --- it has to be flat for 500Kc. If you have aligned it with a peak, it will have an artificially high receive sensitivity at the peak and drop radically at the edges of the band and the transmitter will not work at all away from the peak.

    You can do all of the transmit alignment and neutralization without ever turning on the high voltage.


    Simply wrap a shield around the 12BY7A with a 1 inch length of wire attached to it through a hole and silver solder it. Attach your scope to it, switch to 20 meters. Go to receive and peak the preselector. go to transmit and set tune, xmit, and RF gain at 10. Measure the signal. If it is => than 18 volts PP, it will drive the 8122 to full output. NOTE the hole and silver solder is because the 12BY7A heat will melt lead/tin solder. The 1 inch wire is to keep the heat from melting your scope probe.


    The hottest bands on the SR-2000 and SR-400 series are 15 and 20 meters. 80, 40, and 10 meters are a few db lower.

    Kindest regards Jim K9AXN

     
  3. WA6MHZ

    WA6MHZ Subscriber QRZ Page

    I have lost the signal somewhere around the 2nd transmit mixer. No sig whatsoever to the Driver on any band. I am worried something is up in the bandswitch, but I find no sig on any band.
     
  4. N2EY

    N2EY Premium Subscriber QRZ Page

    Why do you suspect the bandswitch?

    Have the following been checked:

    1) Do you have both the IF and oscillator signals going into the 2nd transmitting mixer? Are they the correct level? How do you know for sure?

    2) Is the 2nd transmitting mixer tube good? How do you know for sure?

    3) Are ALL the electrode voltages on the 2nd transmitting mixer correct? How do you know for sure?

    Only when all those are verified would I suspect the bandswitch.
     
  5. AF6LJ

    AF6LJ Ham Member QRZ Page

    I would look for something more obvious like an open resistor or an open mica cap.
    Unless the bandswitch has been abused it should be okay.
     
  6. K9AXN

    K9AXN Premium Subscriber QRZ Page

    Hi Pat:
    The only thing the band switch could affect at this point is the Hetrodyne oscillator crystal selection. Forget the band switch for now. Let’s start at the inputs to the grid of the 2nd XMIT mixer.

    Pull the heterodyne oscillator tube (V12 the 7056), set the VFO to 14.0, go to tune and MOX (Transmit mode) NO HIGH VOLTAGE FOR ANY TESTING OR ALIGNMENT NOT NECESSARY. The SR-2000 can be completely aligned including Final neutralization never having applied the HIGH voltage.

    The grid of the 2nd xmit mixer will have approximately 2.5 to 3 volts PP at 6.85Mc. If you have that reinstall the heterodyne tube and pull the aux plug in the back of the radio. This will disable the VFO leaving the heterodyne oscillator as the only input.

    Go to transmit at 14.0 Mc and you should see 1.4 volts RMS at 20.5Mc.
    Do that and if all is well we’ll check the output of the 2nd Xmit mixer.

    Relax, we can make that radio work. We have worked remotely with dozens over the years with great success. Folks love to make these instruments work without sending them out.

    Kindest regards Jim K9AXN
     
  7. WA6MHZ

    WA6MHZ Subscriber QRZ Page

    OK Jim, I will get the SR-2000 back out this weekend and give it another try.
    Thanks'
    Pat
     
  8. WA6MHZ

    WA6MHZ Subscriber QRZ Page

    Great SUCCESS!

    I now have RF OUTPUT!!!

    After considerable mousing around with it, along with help from Sue AF6LJ, we were able to nurse it up to about 200W output!

    15 meters is oscillating, so we need to neutralize it

    Also, I have a new set of 8122s I need to install. I see NO DIFFERENCE in output between low power and high power, even though the supply goes from 2000V to 2700V

    I also need to do the Broadbanding trick with the IF Cans so it will be linear across the band. Right now, it is peaked on midband and drops off on the lower and upper ends.

    But we have had GREAT PROGRESS, and looks like this SR-2000 is close to being ON THE AIR!

    Thanks so much, JIM! U were a great help in resurrecting this boat anchor!
     
  9. WA6MHZ

    WA6MHZ Subscriber QRZ Page

    The High Voltage relay seems to have a HAIR TRIGGER on it. U have to push the ON button many times before it will latch on, and then kicks off frequently.

    That won't be easy to fix!
     
  10. AF6LJ

    AF6LJ Ham Member QRZ Page

    It was a very productive day, every dog has its day but in the dog days of summer this dog was laid to rest. :)
     
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