AirKing 4602

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Re: AirKing 4602

Post by 75X11 on Sun Jan 17, 2016 12:35 pm

I couldn't read the value on the schematic.  The total value will be read across the two outer lugs and outer to center should read the up and down  readings with no gaps.  If that is good, and you have replaced the caps around the control, check the fixed value resistors around it before putting it back together.
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Re: AirKing 4602

Post by Wildcat445 on Sun Jan 17, 2016 12:43 pm

I would look somewhere other than the volume control. Go back to the basics, Frank. My understanding is that you have recapped the set. Start with a systematic procedure. Measure element voltages, starting at the cathode of the rectifier. Follow the schematic from the speaker back to the front end. All you have is white noise, right? Is the oscillator running? Do you get a "click" when noise in introduced into the grids? Do you get the old traditional growl when you touch your finger or a plugged in soldering iron to the middle terminal on the volume control?

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Re: AirKing 4602

Post by frank1956 on Sun Jan 17, 2016 5:24 pm

WC,
You are correct the radio has been recapped. The schematic for this radio, that I can find including the one you sent me are not legible at all, so any value negative or positive are a long shot on something I can't read even with glasses on.
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Re: AirKing 4602

Post by 75X11 on Sun Jan 17, 2016 7:14 pm

If the volume control seems alright, connect that portion up again and try the tests WC suggested and let him know what you find. He wants you to be able to "bracket" the problem to a specific area of the radio and then attack the problem from there. That way, you won't be going in more directions than the most likely one.
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Re: AirKing 4602

Post by Wildcat445 on Sun Jan 17, 2016 9:47 pm

You should have 110-125 volts DC on the cathode of the rectifier.  Exact values are not critical at this point.  You should have 110 volts DC or so at the plate of the output tube.  Again, exact value is not critical.  We just need an idea if and where you are losing your radio.  Like 75 pointed out, we need to divide the radio in half to see which half the problem lies in.  Perform some directed tests and eliminate guesswork.  If you have acceptable voltages, then you can take a screwdriver bit and start touching grids, introducing noise into the circuit.  This noise, of course, should be heard in the speaker if all is well.

I remember that schematic not being very good. It is complete enough that we can get an idea of how to proceed. We may have to "guesstimate" some values, but this will not be the first time that has been necessary.

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Re: AirKing 4602

Post by frank1956 on Tue Jan 19, 2016 8:36 am

WC,
Thanks. I will take this approach. I have re-connected everything back to the volume control, preformed the hot soldering iron test to the middle post of the volume control and got a growl out of the speaker.
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Re: AirKing 4602

Post by frank1956 on Tue Jan 19, 2016 10:51 am

Sorry someone might need to walk me through this again in order to take voltage reading. Had a hard drive crash awhile back and any reference material I had was lost!!! Having done this in awhile. Will try and dig up my notes from the last time.
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Re: AirKing 4602

Post by Wildcat445 on Tue Jan 19, 2016 10:52 am

Great! The power supply and the audio section are likely okay then. Have you measured continuity on the IF transformers? There should be a few ohms resistance on each winding if they are good.

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Re: AirKing 4602

Post by frank1956 on Fri Jan 22, 2016 12:09 pm

WC,
Need some guidance in that area? Tried to find my notes I took, but they must have been on my old hard drive???
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Re: AirKing 4602

Post by Wildcat445 on Fri Jan 22, 2016 1:57 pm

It might help if you would post the schematic I sent you on here for reference.  My Riders library is not here, so I'm shooting blind.  

B- on your radio is one terminal of the power switch.  Set your meter to "DC+" range, and at least 150 volts.  Put the black (-) probe of your meter, (VTVM, multimeter, whatever you are using, preferable analog) on this terminal.  The red (+) probe of your meter is placed on whatever terminal you are wanting to measure voltage on.  If you measure resistance (ohms) you would set the meter to "ohms".  You want to make absolutely sure the radio is turned off and unplugged (for safety) when you measure ohms.  You can seriously damage your meter if you apply even the slightest voltage when the meter is set on "ohms".  

Identify the second IF transformer.  It should have four terminals on it.  The primary will be connected to B+ and the plate of the IF amplifier, and the secondary will be connected to the AVC line and the grid of the second detector.  You may not be comfortable finding B+ and the AVC line, but you should be able to identify the other two terminals.  There should be something like 15 ohms resistance in the primary and like 3 ohms on the secondary.  Do not be concerned with minor variations.  We don't want to see infinity.  If you happen to mis-identify the two coils in the transformer, you will measure infinity.  Try other terminals.  Do not get in a hurry, do not become discouraged.  You'll get it, and we'll help what we can. In the interest of simplicity, you do not have to disconnect the IF transformers to check them. Some techs prefer to disconnect, but I am lazy. If we see an discrepancy, we will need to measure voltages for confirmation. The IF's will have to be connected, obviously, to do that. No need to do more work than necessary.

The first IF transformer is connected similarly to the other one.  The primary will be across B+ and the plate of the pentagrid converter (mixer), and the secondary will be across the AVC line and the grid of the IF amplifier.  Similar results will be seen when measuring.  I'm guessing the IF's will be okay, since you are getting hash.  I would think that if one was open, the radio would be more dead, but they should be checked.

I hope this helps.  After you confirm no problem with the IF's, we will go to the converter next.  We are working backwards from speaker to antenna, remember.

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Re: AirKing 4602

Post by frank1956 on Sat Jan 23, 2016 9:52 am

WC,
Per your request. Not sure if I attached the schematics correctly or not??




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Re: AirKing 4602

Post by Wildcat445 on Sat Jan 23, 2016 11:13 am

That will work just fine. Thank you. Have you had a chance to check the IF transformers?

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Re: AirKing 4602

Post by frank1956 on Mon Jan 25, 2016 9:24 am

WC,
Not yet. Been digging out of this 20 inches of snow here in Virginia. I will in the next day or two.
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Re: AirKing 4602

Post by frank1956 on Sat Jan 30, 2016 5:09 pm

Well all dug out cheers WC if I did this right the Primary IF Transformer has 0 ohms on pin 8 of the plate (tube 12SK7) and the secondary has 3-4 ohms (12SQ7) on pin # 1 vice pin# 2 of the grid. I have attached a few pic's

.

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Re: AirKing 4602

Post by Wildcat445 on Sat Jan 30, 2016 5:49 pm

If I read correctly, it sounds like the IF transformer you measured is okay. I expected that they might be. We need to see if the local oscillator is running. You can check the grid of the 12SA7 converter tube (pin 5?) for negative voltage. It will get more and less negative as you tune across the dial, but should always be negative. From -5 to -15 volts AC, give or take a couple. Or you can get another radio, like a little transistor job, and use it to see if the oscillator in the Air King is working. Turn on the Air King, tune it to 600kc. Then turn on the other radio and tune from low to high on the dial. You should hear the local oscillator of the Air King squealing in the other radio at approx. 1055 kc and then at 1510 kc. These two frequencies represent the original frequency (600 kc) and its harmonics, separated by the intermediate frequency (455 kc). 600 +455= 1055. 1055 + 455 = 1510. See what you come up with and let us know. Don't be concerned if you are unsure what the oscillator will sound like squealing in the second radio. It is hard to describe, but is distinctive enough that when you hear it, you'll know. Good luck.

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Re: AirKing 4602

Post by Wildcat445 on Sat Jan 30, 2016 5:55 pm

Another thing, Frank.  You may notice that I did not recommend that you test the 12SA7 converter tube.  That tube can best be tested by substitution.  Pentagrid converters are a particularly finicky lot at times.  One can be perfectly good and still not want to oscillate in a particular radio.  It might work perfectly fine in another set.  I never discard a converter tube unless it is physically broken, or the filament is dead.  If you have another 12SA7, it is always good practice to sub the tube just for grins whenever you suspect a dead oscillator.  You might also wiggle the tube in its socket, and make certain the tube pins are clean and making good contact.  There are several conditions in a radio that will cause the oscillator not to run.  Oscillators are not easy to troubleshoot for some people (like me!)  If we determine, both by the extra radio trick, and by verifying incorrect voltage on the grid of the 12SA7, that the oscillator is for sure dead, we will have to test component by component to find the fault.  Oscillator repair requires LOTS of patience.  Forewarned is forearmed!  Very Happy

If the oscillator is running, as I pray that it is, we will forge ahead to try and localize the fault. Good luck. Very Happy

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Re: AirKing 4602

Post by frank1956 on Sat Jan 30, 2016 7:03 pm

WC,
I understood the primary IF should have at lest 15 ohms? This would be on tube 12SK7 pin #8 the plate correct? If this is the case then I had 0 ohms is that good or bad?? A little confused. Also on the secondary IF 12SQ7 (according to the tube data sheet I looked at on-line pin #2 should be the grid (is that not where I was suppose to take the ohm reading from??) If this is the case then there was 0 ohms from pin #2 on the 12SQ7 and 3 ohms on pin #1 of the same tube. Just need a little clarification before I move on. Thanks again
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Re: AirKing 4602

Post by Wildcat445 on Sat Jan 30, 2016 7:41 pm

Sorry, Frank. I may have gotten ahead of you. Let's back up and try this again.

The primary of the 1st IF transformer (the one closest to the antenna) is pins 3&4 of the 12SA7. The secondary is between pin 4 of the 12SK7 (IF amplifier) and the AVC bus. Approximately 15 ohms or so on the primary and 3 to 5 ohms on the secondary. Again, exact is not critical. We just don't want to see infinity.

The 2nd IF transformer (the one farthest from the antenna). The primary is across pins 6&8 of the 12SK7 and the secondary is across pin 4 of the 12SQ7 (one of the detector diodes) and the AVC bus. The same approximate resistance as on the 1st IF is what we want to see, and again, not infinity. Infinity is not good. Zero ohms is not a concern, as it depends on your meter as to how accurate you will read just a few ohms. You want to set your meter on the lowest ohms setting you can.

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Re: AirKing 4602

Post by frank1956 on Sun Jan 31, 2016 2:38 pm

WC,
Thanks for the information. I have located the primary and secondary IF transformers as well as the corresponding pins. I used both an analog and digital meter for this test. The Analog was set to 1X ohms with no reading from either IF transformer, the digital meter was set to 200 ohms with the same results. These are the lowest setting I have on this meter's.
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Re: AirKing 4602

Post by Wildcat445 on Tue Feb 02, 2016 12:42 am

Just so I am understanding correctly, when you say "no reading" you mean you got a reading of zero ohms, correct?  Not infinity, zero.

If you got a reading of zero, you may be in good shape. Like I explained earlier, depending on meter loading, the small resistance in the IF transformers may read zero or close to zero and be quite normal. It will take a VTVM of pretty good sensitivity, around 20,000 ohms per volt, to read the small resistance accurately.

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Re: AirKing 4602

Post by frank1956 on Tue Feb 02, 2016 7:29 am

WC,
Either meter register any type of reading, so to answer your question zero ohms?? The needle never moved on the analog and no digital numbers where displayed on the digital meter. Make sense??
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Re: AirKing 4602

Post by 75X11 on Tue Feb 02, 2016 9:38 am

Using your analog meter, have you zeroed it? If not, when you set it to the range, in this case the lowest, you put the probe tips together and if the meter needle does not fall on zero, there is an adjustment on the meter front. Adjust it with the probe tips together til the needle is at zero. You must do this again whenever you change ranges in ohms, so you can get good readings. This also checks your battery. This is only for the analog meter. If the needle doesn't move when you are taking a reading, it is reading open, not zero, which is what you should get with the probe tips together.
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Re: AirKing 4602

Post by frank1956 on Tue Feb 02, 2016 2:29 pm

75X11,
Analog meter has been zeroed out. My reading are open and not zero on the meter. (needle does not move)
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Re: AirKing 4602

Post by 75X11 on Tue Feb 02, 2016 3:00 pm

That's good. I just wanted to make sure you were using the meter properly so there would be no confusion. As you know now, zero ohms means a direct short and open means no connection. That will make things go easier when WC gets back with you. He will get you on the right track.
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Re: AirKing 4602

Post by Wildcat445 on Tue Feb 02, 2016 10:17 pm

All four windings on both IF transformers are reading open?  Shocked

What if we try this, Frank.  Turn the radio on, let it warm up for a bit, then measure DC voltage on pins 3&4 of the 12SA7 and pins 6&8 on the 12SK7. There are two 12Sk7 tubes in that radio. You want to measure the one that serves as the IF amplifier, the tube following (toward the speaker) of the 12SA7.  Put the black (-) probe on one terminal of the power switch (B-) and the red (+) probe on whatever pin you want to measure.  Set your meter to DC+ voltage, good for at least 150 volts.  Be sure to observe appropriate safety precautions, both to prevent collateral damage as well as damage to Frank. What readings do you get?

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Re: AirKing 4602

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