Another thing to check is that C1G and C1H are directly in parallel on the lower 3 bands but are connected differently on the upper 3 ranges. Perhaps something is going on with C1G?

Rodger WQ9E

1. I investigated C1G and C1H to make sure that I connected them correctly. As best I can see without disassembly of the RF deck, I did connect them correctly.
2. I also checked the value of C75 with my Amprobe digital capacitance meter. I disengaged the current band and put the probe leads between pin 6 of V4 and the top of C1H to check for a 100uuf value. (I had used a brand new capacitor). The capacitance measured 230uuf. With the band engaged it measured 530uuf. I would think that a value being way off value would explain the behavior, but it have to be a much lower value and not a higher one.

3. As for the plate voltage (pin 1 of V4), here are the measurements for each of the bands:

Band Frequency Plate Voltage
#1 .54-1.35 119.7 V
#2 1.35-3.45 119.6 V
#3 3.45-7.4 119.6 V
#4 7.4-14.8 133.2 V
#5 14.8-29.7 119.7 V
#6 29.7-54.0 119.7 V

The manual states that the V4 plate voltage should be 130V. I wonder if the lower plate voltage on the lower frequencies is problematic? I doubt that a 10-11V difference is significant. Then again, the oscillator oscillates for a dial frequency of 7.4Mhz on band #4, but does not oscillate for 7.4Mhz on band #3.

I think I have to bite the bullet and disassemble the rf deck! Then check each component, the wiring accuracy, solder joints, etc. Ugghhhh!!!

Thank you,

Steffen

Steffen,

check the resistance of the ungrounded terminal (one is grounded through the range components) of C1G, it should be infinity.

Rodger,

Funny you should say that. I just checked to see if the var cap was shorted anywhere. I had to disassemble the stator ceramic in order to clean up some really ugly work apparently done many years ago. C1G is fine, BUT C1C and C1E are at about 0 ohms.

I think I have to clean the test equipment off my bench and start to unsolder.

Steffen

Well, the RF deck has once again been removed for a complete inspection. I will report back for the benefit of those who may experience a similar issue in the future. However, I must admit that I am a bit weary of this unit and need to take a break. Maybe a few days away from it will energize me again. Thanks again.

FOUND THE PROBLEM !

I checked my work 3 times before installing the RF deck the first time. Nonetheless, I made a wiring mistake that passed my inspection process. That is what happens when you work on restorations at 4:00AM. Here is the mistake I made:

I incorrectly wired C74 from the plate of V4 (pin 1) to terminal 2 on S1D (the same post as C79). It is supposed to go to terminal 5 (the connection point for T28 and similar on the 3 lower bands)! This mistaken connection would not be of any consequence on the higher 3 bands due to their circuit design - terminals 2 and 5 on the higher band modules are connected together.

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I want to thank everyone for such excellent support and patience. Here is my contribution to the forum in the form of a lesson learned:

If you are experiencing a problem like the one originally described in this post, or if you are about to embark on an SP-600 like restoration of the RF deck, DO NOT WORK TO THE POINT OF EXHAUSTION AND LEAVE YOUR WORK FOR 1 WEEK WITHOUT TOUCHING IT BEFORE MAKING YOUR FINAL INSPECTION PRIOR TO REINSTALLATION. The design of the SP-600 RF deck is unforgiving and you lose all objectivity after many hours and consecutive days of restoration work.

Thank you all again,

Steffen

Steffen,

I am glad you located the problem and now you can enjoy the receiver.

You have learned a valuable lesson pretty inexpensively. When working beyond fatigue you are putting both yourself and the equipment at severe risk. The odds of making a mistake resulting in injury or death increases exponentially with increasing fatigue and the resulting lack of focus and attention. I live in the heart of midwestern agricultural country and the worst accidents tend to occur near the end of planting and the end of harvest time. In both cases you have individuals pushing themselves and their equipment to meet deadlines and the results are often very unfortunate.

I also learned early in woodworking that a couple of hours is my limit without a break, fortunately the worst I have done so far is that I have made mistakes that ruined a piece of wood but I still have all of my fingers.

The good news is that odds are your next few restorations will be fairly simple ones and it isn't a bad idea to choose a couple of restful projects before going after your next difficult restoration. After restoring the front end of my Pierson KP-81 I did a couple of simple AM/CW transmitter restoration before moving on to a Collins KWM-380 with power amplifier issues That was a good choice.

Rodger WQ9E

Congratulations, Steffen. Your perserverance paid off and now you can enjoy one of the best SW receivers ever made.

Joe Connor

Stephen,

Congratulations, Glad to see you have it up an running.

Yeah, same thing happens with software, I can be getting nowhere for hours, but if I take a stroll to the Fritos machine, quite often that helps a lot. Quite often the solution just pops into my head in the hallway.