Hi everyone. In new to troubleshooting older radios an need some help. I have a Knight Kit Star Roamer that was purchased from ebay a few years ago. Tried it out but got only a squeal out of it. Just now getting to troubleshooting. There are no stations heard on any band. Antennas were hooked up properly. I began probing and found that I could inject a 455khz signal in front of the detector and get a clear signal in the speaker. I move that same signal to pin five of V2 and get a very weak signal. I tuned the can using my scope for max throughput. However the signal remains weak when injected into the front side of the can. This occurs with either power on or off. I have done a recap and replaced the selenium rectifier with a 1n4005 diode and an appropriate droping resistor. Not sure what to do now. Resistance across the pins of both cans are very close to each other so Im thinking the caps in the cans are ok. Something else I noticed is when this unit is plugged in and turned on I get either 168v ac or 64 vac from the chassis to earth ground depending on how its plugged in at the time. I was under the impression that with the transformer as shown in the schematic thai it should be isolated and should not get any reading to earth ground. Im kind of stumped..

 

Let me amend my above statement. I was able to tune the can for max output using a scope while the power was off on the radio whilw the sig gen was hooked to pin 5 of v2 but only hear a very faint signal out of the speaker. Its much stronger when injected directly in front of the detector.

 

If radio off you would hear a very weak signal out of speaker.

Best to tune radio powered up. That's because reflected Z's due to gain circuits
powered up can change the effective values of L and C in tuned circuits.

Inject into pin 1 of V2.

How are you injecting signals, thru a real small cap ?

Regards, Dana.

 

Am I correct in assuming that the 455 khz signal is modulated with an audio tone ? Did you inject this signal into pin 3 or pin 4 of the IF transformer ? Are you sure that the IF frequency is 455 Khz ? (It probably is but if it is not then the IF transformer would pass very little signal.) Does the output of your signal generator have a DC path to earth or is it AC coulpled ? (If it does have a DC path to earth then it will short out the HT to the anode (Pin 5) of V2) Have you confirmed that neither the primary or secondary windings of the second IF transformer are not open circuit ?

Edit. I have just noticed Dana's comment about injecting the signal via a very low value capacitor. That is a very good point that I had not thought of.
Les.

 

What happens when you put the IF signal into pin 1 of V2 the If amp?

 

Just as a thought.... It's a Knight *kit*. Someone put it together and you have no way of knowing if it ever worked properly. Do a close comparison to the schematic, checking pin numbers and solder connections. Be sure the IF transformers are installed correctly.

The schematic has DC voltages listed. Check those. Let us know an significant discrepancies.

I had one of these - remember it being a rather poor performer. Much preferred the R-100A.

 

If radio off you would hear a very weak signal out of speaker.

Best to tune radio powered up. That's because reflected Z's due to gain circuits
powered up can change the effective values of L and C in tuned circuits.

Inject into pin 1 of V2.

How are you injecting signals, thru a real small cap ?

Regards, Dana.

I tuned the IF can using my scope when the imput was on the plate of v2. Did not want to use the scope because Im getting some sort of continuity from the chassis to earth ground when the radio is pluggeg in. I am using a .06 mf cap to inject the signal.

 

Am I correct in assuming that the 455 khz signal is modulated with an audio tone ? Did you inject this signal into pin 3 or pin 4 of the IF transformer ? Are you sure that the IF frequency is 455 Khz ? (It probably is but if it is not then the IF transformer would pass very little signal.) Does the output of your signal generator have a DC path to earth or is it AC coulpled ? (If it does have a DC path to earth then it will short out the HT to the anode (Pin 5) of V2) Have you confirmed that neither the primary or secondary windings of the second IF transformer are not open circuit ?

Edit. I have just noticed Dana's comment about injecting the signal via a very low value capacitor. That is a very good point that I had not thought of.
Les.

Yes. The gen is modulated with a sweep signal from 60 to 1000 hz. Its ac coupled with the cap. When I inject at pin three or pin 4 of the transformer I get a good signal through the AF section. I ohmed both of the cans and they all ohm out within a fraction of an ohm to each other. Im beginning to suspect that my power transformer primary may be touching ground in the winding.

 

If radio off you would hear a very weak signal out of speaker.

Best to tune radio powered up. That's because reflected Z's due to gain circuits
powered up can change the effective values of L and C in tuned circuits.

Inject into pin 1 of V2.

How are you injecting signals, thru a real small cap ?

Regards, Dana.

I also tried to inject the signal at pin one of v2 but it is still very weak.

 

Just as a thought.... It's a Knight *kit*. Someone put it together and you have no way of knowing if it ever worked properly. Do a lose comparison to the schematic, checking pin numbers and solder connections. Be sure the IF transformers are installed correctly.

The schematic has DC voltages listed. Check those. Let us know an significant discrepancies.

I had one of these - remember it being a rather poor performer. Much preferred the R-100A.

Yes. I checked the cans and they are in correctly. I had replaced the caps in the power supply and had to put a compensating resistor in because of putting in the 1n4005. The voltages are all well within spec.

 

What happens when you put the IF signal into pin 1 of V2 the If amp?

I get a very weak signal. Similar to injecting to the if can.

 

If the IF is in fact 455 khz sounds like V2 the if amp is not working.
Are the voltages on V2 correct?
if so Inject the signal using the small 10pf or so cap on Pin 1
see if it increases on pin 5.
make sure your using a high impedance scope probe and the small capacitor to inject it.

 

I get either 168v ac or 64 vac from the chassis to earth ground

Earth ground? You mean the safety ground on the power plug?

With the unit unplugged, turn the power switch on. Use your ohmmeter to check for any leakage between either of the power plug prongs and chassis.

If you still feel there may be voltage on the chassis, you could take a small 120 VAC incandescent lamp and connect it between chassis and that 'earth ground'. See if it lights up. I suspect you are just reading leakage currents and those are likely in the sub-mA range.

 

When I inject at pin three or pin 4 of the transformer

Injecting at pin 3 should produce a weaker response than injecting at pin 4. Pin 3 has an RF bypass on it.

Remove V2 and inject that 455 KHz into pin 2 of the transformer through a small capacitor. !! Caution, 60 V or more B+ at this point. Make sure the cap is rated for 100 volts or more. The response should be very similar to what you get injecting at pin 4.

Not quite sure what they are doing with the pot on the screen grid of v2. The input posts for a 'key' on the output leads me to believe the unit can be put into a mode where it is oscillating and you can use it as a code practice oscillator.

 

Full manual here: https://elektrotanya.com/allied_radio_corp_knight-kit_star_roamer.pdf/download.html

 

Something that may make a difference. Im using a 2v signal from the sig gen. I dont know how much the circuit would need to have to get a proper signal.

If the IF is in fact 455 khz sounds like V2 the if amp is not working.
Are the voltages on V2 correct?
if so Inject the signal using the small 10pf or so cap on Pin 1
see if it increases on pin 5.
make sure your using a high impedance scope probe and the small capacitor to inject it.

All voltages are correct. Im usinf a .06mf cap to inject. I dont thinknit can be v2 since when I connect to pin 5 which is the output of v2 i still getba weak signal.

 

2 volts is going to be a severe overload. Drop that level into the mV level. Perhaps 100 mV at the IF output, no more than 10 mV at the input of the IF amplifier. You want the test signal to be as low as possible consistent with a measurable output.