hallicrafters SR-2000 time delay relay?

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

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  1. K9AXN

    K9AXN Premium Subscriber QRZ Page

    Hi Pat:
    Haven’t been watching the forum --- apologize.

    Don’t be pulling any hair out yet. We fix these guys remotely with a very good success rate. Nobody likes to ship the P-2000.

    Some hints on no transmit:

    1. You can verify transmit drive quite easily. Make a round copper shield like a tube shield, drill a hole in the upper edge and silver solder a 1 inch length of wire to it. If you intend to do any other non- intrusive measurements on these beauties, this will be one of your favorite tools from front to back. While you’re at it make one for the 7 pin size tube. You will measure about 2pf to 4pf from the plate to shield. The reason for the wire and silver solder is the 12BY7A gets so hot that it will melt regular solder. The wire isolates the heat from the scope probe that you will attach.


    1. NOTE: Complete alignment and testing throughout the SR-2000 can be done without ever turning the HV on --- including neutralizing the finals.


    1. With the HV OFF: Attach your scope probe to the shield that you made for the 12BY7A. Set band switch to 20 meters and transmit RF to full 10. Go to transmit tune and vary the pre-selector. Full drive would measure approximately 15 volts PP on the shield. With that level the 8122’s would provide 500 watts to the antenna or 1000 watts input.


    1. The sequence that I would use to bring that radio to life is Verify the oscillators are all on and at the appropriate levels. The first LO measurements RMS and are in the manual and should be measured with an HP 401 B or C meter or equivalent. Your 10X scope probe will warp the measurement. The carrier oscillator is not and will be from 4 volts to 6 volts PP. The VFO should read about 1.2 to 1.8 volts PP at the cathode of the second receive mixer. BTW there are no mixers in the receive circuits and only one in the transmit logic --- the second transmit mixer. THEY ARE MORE PRODUCT DETECTOR THAN MIXER.


    1. A good measurement that represents everything up to the second transmit mixer is V11P2. Simply go to transmit and you should find 2.5 to 3 volts PP. While you are there, vary the VFO throughout its range and note the variation in voltage. Should not exceed 3db. If it does, T1 and T2 have probably been tampered with. They are the 6.5Mc I.F. transformers and are tricky to adjust. The procedure is not in the manual. Bob Orwin the chief engineer at Hallicrafters once wrote that that adjustment is for experts only. We developed a simple procedure that anyone can be successful with. It can be found at www.k9axn.com in the service notes section. The first method is accomplished with sweep analysis and is difficult. The second method which does an excellent job uses the ancient swamping method, an all but forgotten procedure for broadband amplifiers. Sweeping this adjustment is unusually difficult because the 6.5Mc I.F. is composed of a double tuned transformer, amplifier, and second double tuned transformer. There are photos to describe what you are doing.


    1. The tube shield method of extracting non-disruptive measurements is used throughout the radio. For lower level measurements i.e. the level out of the receive RF amplifier, we simply slip the shield over the tube and attach the scope probe to an HP 8447D 26db pre-amp which is then attached to an HP 8568B spectrum analyzer. With this combo you can tell not only the amplitude but the frequency content. With a 3uv PP signal at 14.0Mc injected into the antenna lead. You should see a 60 to 70 uv signal on the 8568B. These measurements can be extracted throughout the radio and are all recorded during sea trials after a restore.

    Hope you find this helpful and maybe interesting. I do not edit what I write so if you find grammar or intellectual errors send a note and I’ll fix it.

    Kindest regards Jim K9AXN
     
    Last edited: Jul 3, 2013
  2. K9AXN

    K9AXN Premium Subscriber QRZ Page

    Hi Pat:
    There is a grid connection outside for the 8122's. It is at the front of the enclosure adjacent to the 12BY7A. It is simply a wire through a plastic spacer.

    Kindest regards Jim K9AXN
     
  3. K9AXN

    K9AXN Premium Subscriber QRZ Page

    SR-2000 Additional test methods for transmit mode

    Good morning Pat:
    Where did you measure the output of the balanced mod? It will normally be unbalanced in CW and Tune mode and no adjustment of the balance control will affect the output. The output in CW and Tune mode is caused by imbalance from the 150 volt line applied to one side of the bridge through a resistor. In USB and LSB mode the balance controls will be adjusted for a null when there is no audio. You can do this adjustment using the shield on the 12BY7A rather than the transmitter output.

    Last note: A quick test of the whole drive system all of the way through the grids of the 8122 without enabling the HV is to tune the radio up in receive mode, go to transmit, set the transmit audio to 10 and speak into the mike. Set the meter switch to AALC and note the needle movement, a result of the 8122 grids being driven to conduction. The AALC is to limit the 8122 to AB1 mode.

    Kindest regards Jim K9AXN
     
  4. K9AXN

    K9AXN Premium Subscriber QRZ Page

    Pat, Do not give up on that radio. There are no SR-2000's that should be religated to retirement. Never have seen one that could not be fixed.

    Kindest regards Jim K9AXN
     
  5. K9AXN

    K9AXN Premium Subscriber QRZ Page

    Good show Sue! Good and welcome comments. Been working with these radios since they were born and restoring them as they age. I am retiring from the restore work and significantly limiting the service work and am looking for folks that are interested in working with these place holders in history. Lot of people are uncomfortable working on a complicated, high power transceiver, all wrapped up in a very small package.

    Kindest regards Jim K9AXN
     
  6. AF6LJ

    AF6LJ Ham Member QRZ Page

    Good Stuff Jim.
     
  7. K9AXN

    K9AXN Premium Subscriber QRZ Page

    Correction

    Guess I should have edited the data. Red indicates the error --- should have been millivolts not volts.

    The sequence that I would use to bring that radio to life is Verify the oscillators are all on and at the appropriate levels. The first LO measurements RMS and are in the manual and should be measured with an HP 401 B or C meter or equivalent. Your 10X scope probe will warp the measurement. The carrier oscillator is not and will be from 400mv to 600mv PP. The VFO should read about 1.2 to 1.8 volts PP at the cathode of the second receive mixer. BTW there are no mixers in the receive circuits and only one in the transmit logic --- the second transmit mixer. THEY ARE MORE PRODUCT DETECTOR THAN MIXER.


    A good measurement that represents everything up to the second transmit mixer is V11P2. Simply go to transmit and you should find 300mv PP. While you are there, vary the VFO throughout its range and note the variation in voltage. Should not exceed 3db. If it does, T1 and T2 have probably been tampered with. They are the 6.5Mc I.F. transformers and are tricky to adjust. The procedure is not in the manual. Bob Orwin the chief engineer at Hallicrafters once wrote that that adjustment is for experts only. We developed a simple procedure that anyone can be successful with. It can be found at www.k9axn.com in the service notes section. The first method is accomplished with sweep analysis and is difficult. The second method which does an excellent job uses the ancient swamping method, an all but forgotten procedure for broadband amplifiers. Sweeping this adjustment is unusually difficult because the 6.5Mc I.F. is composed of a double tuned transformer, amplifier, and second double tuned transformer. There are photos to describe what you are doing.
     
  8. WA6MHZ

    WA6MHZ Subscriber QRZ Page

    Thanks so much, Jim!

    I will try all those.

    I am thinking there is something fishy with the Balanced modulator. I see great audio and Rf from the Carrier osc going to it, but don't see much if any output. I don't see any change when I vary the carrier Null pot. Maybe that pot is open. I do see good audio signals at the junction of the 2 bal. mod diodes, but I should see RF at that point too.

    If I can't get RF out of the Balanced modulator, I am not going to get it anywhere else down the line.

    Probably will get it on the table again Saturday when the boss is out. One thing I planned on doing is making measurements on the SR-400 which seems to have the Same balanced modulator circuit as the 2K.

    Thanks again and 73!
     
  9. N2EY

    N2EY XML Subscriber QRZ Page

    OK, I'll bite.

    What's the difference between a "mixer" and a "product detector"?

    The way I learned it, a "mixer" in this context takes two signals of different frequencies (one of which is usually a local oscillator of some kind), mixes them together and produces output at a third frequency which is either the sum or difference frequency. Also present in the output are the original two frequencies, harmonics, and other mixing products which are removed by filtering.

    A (single) balanced mixer, aka "balanced modulator", is a mixer which has circuitry so designed that one of the input signals is internally cancelled. For example, in an SSB transmitter, the "balanced modulator" is so designed that the carrier oscillator frequency does not appear in the output.

    A double balanced mixer is a mixer which has circuitry so designed that both of the input signals are internally cancelled.

    A product detector is just a mixer optimized for receiver use. It may be a plain mixer, single or double balanced.

    What am I missing?
     
  10. K9AXN

    K9AXN Premium Subscriber QRZ Page

    Ignore this note, the original was correct. One of the folks that read the original sent an email while I was out of pocket saying that the measurements were an order of magnitude high. They were not, his scope probe was in trouble.


    Kindest regards Jim K9AXN

     
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