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Author Topic: Knight R100A Receiver  (Read 611 times)
KF0QS
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Posts: 65




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« on: January 22, 2019, 10:07:50 AM »

My very first rig was a Knight R100A receiver and a Knight T60 transmitter.  I can't tell you how much pure joy I had tuning around both the ham bands and the international broadcast bands with that receiver.

Years ago, I found an R100A/T150 pair (the T150 is the actual matching transmitter to the R100A) on eBay and got them.  Since then, I've had the R100A (and the T150) looked at by a repair guy who replaced the capacitors, and I replaced every single tube.  The receiver is now stable (if you let it warm up for about 30-45 minutes - I remember doing that in my novice days) but it has a consistent hum that is not responsive to the volume control, the S meter isn't very responsive, and I seem to have lost the ability I had as a novice to use the Q Multiplier to narrow the bandwidth.  I have made contacts with the pair (I use crystal control with the T150, since its VFO is worthless), but I miss having the receiver performance I recall.

Of course, my main rig today is the Elecraft K Line, so the Knight gear obviously suffers by comparison.  Also, my memory is likely somewhat faulty at this point (I had the Knight gear in the late 60's and early 70's).  Still, I know that the S meter and the Q Multiplier don't work the way that they're supposed to work, and I've tried a better ground and several other measures to get rid of the hum, unsuccessfully.

Is there someone out there who works on Knight gear professionally?  I'd love to bring this receiver back to what I remember and lack the technical ability to take it further.
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KD0REQ
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« Reply #1 on: January 22, 2019, 12:34:56 PM »

steady hum not responsive to the volume control is AC riding on the plate of the audio amp tube.  this is probably the first section of the filter capacitor bank. worth tack-soldering another electrolytic across that capacitor and see if it reduces or goes away.
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KE4OH
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« Reply #2 on: January 23, 2019, 06:42:24 AM »

I have 2 pair of KnightKit Twins. One is in mint condition, the other pair works to a degree, but I consider them future part units.

The hum could be from any number of causes. Bad filter capacitor. A tube with a heater to cathode short. But if the caps and tubes are good, a bad ground is a likely candidate. Get out your screwdriver and pliers and tighten every single screw and nut in the thing. These were kits, so soldering skills of the builder are always suspect. Reflow all solder joints on the PC boards and all terminals. All of them. Get a magnifying glass. Look for fly leads and stray "whiskers" that might be making contact somewhere that they shouldn't.

Regarding the S-meter... The S-meter will only work correctly if the BFO is off and the mode is set to AVC. Then the RF gain must be fully clockwise. If it still doesn't move much, you probably have one or more resisters in the AVC circuit that have drifted out of spec.

Now, the Q-multiplier. To me, this is the best feature of a radio that I consider beautiful, but overly complex and poor performing. Don't bother with the Notch setting. Stick to Peak. Start with the Q-mult Tune control in the 12 o'clock position and the Sensitivity fully counter clockwise. When you have the signal tuned in, rotate the Tune control until that signal peaks. Then turn the Sensitivity control clockwise as far as you can. When it oscillates, back off. Now you should have a nice, sharp peak so that you can hear just the signal you want. That's how I do it and it works well. If this doesn't work for you, there may be a circuit problem.

Regarding the T-150, the VFO isn't that bad. There is a mod, easily found with a Google search, that changes an RF choke (and maybe a resistor) that greatly improves stability. I use mine on the air frequently. It isn't completely chrip-free, but it doesn't drift.

73 de Steve, KE4OH
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73 de Steve KE4OH
HAMHOCK75
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Posts: 551




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« Reply #3 on: January 23, 2019, 03:47:38 PM »

The T-60 was my first commercially made transmitter but I never saw an R100A until recently. One of our best surplus stores in the local area went out of business on January 12th. On their racks at 1/2 price was an R100A with the matching S8A speaker said to be in working condition. I bought it to go with my DX60B. From what I can tell, the R100A is not a sought after receiver and does not command a very good price. I can see that shipping back and forth alone would be more than I paid for it let alone the cost of repair.

You might be better off selling yours and just buying a working one.
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KF0QS
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Posts: 65




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« Reply #4 on: January 23, 2019, 11:42:15 PM »

Quote
Regarding the S-meter... The S-meter will only work correctly if the BFO is off and the mode is set to AVC. Then the RF gain must be fully clockwise. If it still doesn't move much, you probably have one or more resisters in the AVC circuit that have drifted out of spec.

Now, the Q-multiplier. To me, this is the best feature of a radio that I consider beautiful, but overly complex and poor performing. Don't bother with the Notch setting. Stick to Peak. Start with the Q-mult Tune control in the 12 o'clock position and the Sensitivity fully counter clockwise. When you have the signal tuned in, rotate the Tune control until that signal peaks. Then turn the Sensitivity control clockwise as far as you can. When it oscillates, back off. Now you should have a nice, sharp peak so that you can hear just the signal you want. That's how I do it and it works well. If this doesn't work for you, there may be a circuit problem.

Duh!!!  Thanks for this valuable lesson in remembering to read the instructions.  I had completely forgotten both of these things about the R100A. 

I have now had the radio on and followed both of these techniques (which I had forgotten given the almost 50 years since I last operated my old R100A), and it worked quite well.  Indeed, I zoomed in on a CW signal using the Q Multiplier and it worked just fine.  It was almost like, as soon as the Sensitivity control caused oscillation, I remembered doing it a million times as a teenager.  I had just forgotten.  So, now all I have to do is work on the hum, which isn't bad when the radio is receiving signals (it's only prominent when the receiver is quiet).

Thanks for the help.  And, it's a good thing I'm used to feeling stupid.   Wink

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HAMHOCK75
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Posts: 551




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« Reply #5 on: January 23, 2019, 11:59:08 PM »

Quote from: KF0QS
So, now all I have to do is work on the hum, which isn't bad when the radio is receiving signals (it's only prominent when the receiver is quiet).

Is it possible that the hum is also not produced by the R100A? When I bought mine it had terrible hum. I had heard that LED lights could cause interference. I started turning off lights. When I turned off a three LED fixture in the kitchen, all the 60 Hz radiated interference vanished.
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AC5UP
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« Reply #6 on: January 24, 2019, 01:31:02 AM »

On older receivers with a two prong non-polarized power plug you may find the hum reduces if you turn the power plug 180 degrees.
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KF0QS
Member

Posts: 65




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« Reply #7 on: January 25, 2019, 11:18:32 PM »

As a postscript, after following KE4OH's advice, I got on the air yesterday with the Knight pair, and in short order worked two stations on 40 meter cw in the late afternoon.  On one of the QSO's, I got a 579 RST, and on the second, the other station was very weak, and using the Q Multiplier, I was still able to copy most of what he sent.

The hum is still there, and I will use the suggestions on this thread (particularly the one about checking all the screws in the chassis and checking the solder connections) to try and find the culprit.  It's interesting how, when the radio is being used properly, the hum is minimized.

Finally, here's some irony.  I periodically check eBay for a Knight T60 transmitter (so that I can recreate my novice station completely).  Yesterday I saw one, and ended up placing the only bid on it and got it!  The seller says it's fully tested and functional.  I am looking forward to making my first QSO with my old novice station.

Thanks again, for all you guys' help.  73.
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