Phantom 19 IF Alignment Help

[Joe Miller]

Just finished recapping it, powered up and it sounds great.  I noticed that they eye tube doesn't close on a strong station (see link from ARF below on details)

http://antiqueradios.com/forums/viewtopic.php?f=6&t=199147&...

 

Anyway, I want to check the IF alignment to see if that will raise my gain, increase the AVC (negatively) to the eye tube, and cause it to fully close on the strong station.  I'm somewhat skeptical that I could be losing that much gain because the radio sounds so good and loud on the strong station already.

 

Does anyone have experience in aligning a Phantom 19?  Would appreciate any hints anyone might have.  The instructions I have are a bit vague.  I think I can figure it out, but would like any input any of you might have.

 

Thanks,
Joe

[Bill Liers]

 

Joe,

 

There is nothing vague about the alignment procedure that I can see. If you are not familiar with this type of alignment, this may not be the one to start on. It might be advisable to get help although there are ways of aligning the set which are a bit simpler.

I suggest that you check the AVC voltage coming to the eye tube with a strong signal coming in. Use a digital meter on this if you can as it's high impedance. If it's in the negative 5 to 10 v range or higher, it may be that the 1 meg ohm resistor across the eye tube has drifted as they usually do. This reduces the sensitivity of the eye significantly. Did you know that it sits in the eye tube socket? Were all the resistors measured when you performed the recap?

 

regards, Bill

[Joe Miller]

Hi Bill,

I've checked the things you've mentioned.  All caps replaced, high ohm resistors are reasonable, 1 meg resistor in base of eye tube socket is good, max AVC at both the grid of the eye tube and the main AVC bus (they are separate) is -2.5 volts.  Both sides of the 6H6 detector are -2.5V max when a strong station is tuned.  Only thing left is loss of gain.

I'm going to connect 455KC and see if I can get some more gain out of it.  I assume the adjustments for the IFs are the two screws underneath each of the IF cans?

Joe

[Bill Liers]

Joe,

 

To determine if and how much the alignment is off, the quickest approach is to monitor the AVC voltage while applying 455 to the grid of the converter. Short the antenna and set the level for -2.5v AVC . RF gain to max, sensitivity to sharp and see what you can get. Start at the detector side and go back to the converter. Adjust for max neg voltage, backing off the generator as you make improvements. You will have to repeat a number of times to insure that everything is peaked exactly at 455. It should only take a small adjustment of each screw so go slow. I imagine that you've tested all the tubes?

 

And yes, those would be the correct screws. Also, when you recapped, did you change the caps in the IF cans?

 

good luck, Bill

 

[Joe Miller]

Bill,

Thanks for the tips, I will try it today or tomorrow.

The general alignment instructions I have say to ground the AVC bus, but I never do.  I assume I don't ground it using your approach since I will be using the AVC bus to peak the IF's...correct?

 

Yes all tubes are good and I even substituted another good 6K7 in each IF stage to confirm there wasn't a bad IF tube.

Also, yes I did replace the caps in the IF cans too.

Thanks again,

Joe

[Bill Liers]

Joe,

The reason AVC is disabled during alignment is so that a direct gain measurement can be obtained without the AVC trying to compensate by bringing the gain back down. These days we have high impedance meters so we can use the AVC voltage as a gauge of relative RF/IF gain. It's convenient, but eventually you should test for usable sensitivity to see how close you are to factory specs.

good luck, Bill

[Joe Miller]

Bill,

Hooked up my sig gen and frequency counter to align the IFs.  My as found condition is a somewhat weak peak at 480KHz rather than 455 KHz.  I didn't adjust anything because this seems very strange.  The set has decent reception--only reason I am attempting alignment is to get the AVC up enough to close the eye tube on a strong station.  Is it possible this set could receive as good as it does with IFs apparently so misaligned?

Should I set my sig gen for 455 and begin tweaking the IF adjustments to get the best peak?  I can't believe it is this far out of IF alignment and still have good reception??

Thoughts?

Joe

[Joe Miller]

Oh and by the way,  I connected my sig gen to the grid cap on the converter tube through a .1 mf cap.

[Bill Liers]

Joe,

 

It's fairly common for owners to tweak the adjustments without a generator or procedure for that matter trying to compensate for an unrelated issue. 480 is not so far off that the transformers can't tune however they are far more efficient at the 455kHz they are designed for. I have a feeling you will be amazed at the improvement. If you don't get enough gain with a 455 input to hear anything. step down slowly setting the gen at 470 then 460 and finally at 455 for example.

and .1mf is fine.

regards, Bill

[Norman S Braithwaite]

Prior to adoption of 455-khz as a standard (and maybe even after) Scott aligned the IF amplifiers to a range of frequencies ranging from 465 to 480-khz depending on potential interference at the buyers location.  During production of the AW-23 receivers, if not 465-khz, the IF frequency was noted on the inside back apron in grease pencil.  I have not noted this practice on later chassis but Scott continued to use a range of IF frequencies.  Within a reasonable range, the sensitivity of the receiver should not be affected much by the exact frequency to which the IF amplifier is aligned.  If not clear by a grease pencil marking or a distinct IF peak at the IF frequencies employed by Scott, I align Scott receivers to 465-khz.

Norman

[Bill Liers]

Norman,

It's certainly true that the exact frequency over this range should make little difference as long as all ducks are in a row. I have noted however that some radios have a better Q at the low end of the transformer range and therefore somewhat better gain overall. I have attributed this to the aging and some amt of shrinking of the coil forms and insulation, bringing up the inductance value slightly. I see little downside to setting up the IFs for max throughput other than a break with convention. Comment?

 

regards, Bill

[Joe Miller]

I checked to see if there was an IF frequency noted in grease pencil on the chassis but didn't find anything.  (Did find UU234, 12/10/40 though marked on the bottom cover).

Do you think this procedure will work?

Since I can hear the tone at 480, adjust  for max peak there, then,

Adjust the sig gen for 475 and adjust for max, then,

Adjust the sig gen for 470 and andjust for max, then,

Adjust the sig gen for 465 and adjust for max.

Do you think I should leave it at 465 rather than try to go all the way to 455?

 

ORRRRR

 

Should I just try to peak it at the 480 where I currently hear the tone and leave it there?

BTW how high should the AVC be on a strong station when the set has a well aligned IF section?  I assume it should be much higher than the -2.5 I have now.  Should I expect the set to be more sensitive too?

[Bill Liers]

Joe,

For fun try to peak it at 480 and see what you get on the avc. Then try 465 as Norman suggests. Convention suggests you use whats listed on the alignment sheet, but unless one is significantly better, it doesn't matter much?
The actual voltage is proportional to the signal level at the antenna but should be well over ten on a strong station.

Regards, Bill