[w5ami]

I'm just about to throw in the towel, so thought I would put this out there for the experts who may have a clue, or direction for me to go. I have entitely recapped, replaced all but about three resistors, and just today replaced the micas in the Osc and RF sections. Only caps I have not replaced or checked yet are the fixed ones inside the 3rd IF xfmr.

I have checked both the antenna and osc coils at least 4 or 5 times, and they have continuity as they should. I have tried at least three XXL's, and the one I have in there now tests well above minimum on a TV-3/C.

I have cleaned and checked the tuning condensor for trash, and bent plates.

I have soldered all riveted ground lugs to the chassis in the area of both the RF and Osc. All wires have been replaced. Bandswitch cleaned and inspected, and all IF xfmrs check good for continuity.

I have not taken any time to align the other bands, but I do hear SW stations on the 9 - 12 mc band, but not sure they are where they are supposed to be. I also hear a lot of what sounds like birdies on the upper band.

I have aligned the IF with my Motorola 1200 @ 455kc per the instructions. I should mention that I get two peaks on the IF with the slug on the 1st xfmr. One nearly all the way in, and one out quite a ways. Not sure what that's about, but using either peak does not seem to affect my problem.

Here is a schematic I posted the other day to the forum on another question I had:
http://philcoradio.com/phorum/attachment.php?aid=1749

The primary problem is this:
While attempting to adjust (with trimmer 16) the HF osc for the BC band at 1500 kcs, I can hear what I think are only images, and only two where the trimmer is nearly fully compressed.

I can not hear anything at 550 kcs, so I am unable to attempt alignment there.

Reason I think the signals I hear are images is that once I align one of them and try to hear stations on the BC band, there is nothing but static. I can however just start turning 17 out and hear BC stations going by, but if I set one dead on with 17, it is extremely wide and no other station can be heard using the tuning condensor, just that one nearly 1000 kcs wide!

Inserting the antenna does have a great effect on reception of static and strength of the BC stations I can tune in using trimmer 17.

I have measured the voltage at the grid of the XXL Osc the best I can without a VTVM, using a scope, and see only about -2 volts. Assuming that's correct, I would think it's not enough negative. What should it be? The plate voltage on the XXL Osc shows 40+ volts, and about 95 on the XXL 1st det.

The real mystery is where I find the LO using a ICOM 746. I can only find one. Setting the tuning condensor at the top of the band, about 1700, the LO is heard at 1292 kcs, and at the bottom, about 550 kcs, the LO is heard at 1244 kcs.

I'm at a loss at this point. Only thing I haven't done is replace tube sockets.

Since I have temporarily removed the push button assy., I can not check it, but my next step might be to re-install it to see if I can get them to work with thier own tuned circuits.

Yes, I have inspected my replacements, caps, resistors, and wire just in case I tied something to the wrong terminal, but I plan to go over it once more since I'm just not getting anywhere with this. I hope my lengthy description covered everything and makes some sense.

Any help will certainly be appreciated and very welcome. I just feel like I've hit a brick wall.

TIA
Brian

[BrendaAnnD]

Check to make sure your tuner rotor has a good connection to ground. If it doesn't, it will cause this problem. Basically, you have indicated that over the range of the tuner, you are getting almost no capacitance change. Additionally, you have no reception at the bottom of the band, which also indicates insufficient capacitance to tune the lower frequencies. This condition doesn't affect the SW frequencies as much, though it does to some point, e.g. you can tune a smaller range of frequencies than what is intended, and likely these will be higher in frequency. As far as BC band, you are tuning all stations with the trimmer. When you use the tuner, you are moving the LO only a tiny amount, so your tuning appears wide, and the peak will be in only a small part of that. Additionally, with the frequencies you indicate for your LO, it would appear that you will only receive stations in a range of approximately 800-850 KC.

To reiterate, check for ground continuity from the tuner rotor. It has to be on the order of less than 1 ohm (0.14 or so). You may have a bonding strap loose, or you may need to clean the rotor bearings with something like DeOxit (or both).

[Mondial]

It seems that there may be some issue with the bandswitch sections related to the local oscillator. When in the pushbutton tuning position the variable tuning cap is isolated from the circuit and replaced with a fixed value cap. Perhaps there is oxidation on the switch contacts (section A8 ) which connect the variable cap to the oscillator coil?

There is an awful lot of switching going on in that osc circuit and any bad contacts may cause loss of tuning range.

[w5ami]

Both good suggestions. I have the variable out now, soaking in Simple Green and hot water. Wasn't as clean as I thought it was, as the solution is already muddy looking... I will use distilled water as a final rinse on it. Will be tomorrow before I'm done with that and reinstall it.

That bandswitch is a booger, and hard to see and get to all the contacts. While the tuning condensor is soaking, I will see if I can get better access to some of those contacts with something. I am out of deoxit, so may need to get some for this. I used regular contact cleaner, but don't think it's up to the job. I am still baffled about the LO frequencies I'm seeing. Makes no sense...

[Radioroslyn]

Another thought is someone may have played tighten up all these loose screws and knocked your alignment way out...
GL
Terry

[w5ami]

I reinstalled the tuning condensor after cleaning it very good and burnished the leaf spring contacts, and rotor where it rubs them, etc. No change in the problem on the BC band. At least the condensor looks nice. It has a good ground, no problem there. I soldered all the riveted lugs in and around the osc and rf sections to the chassis, and as a feel good thing, I installed some screws with star washers on the chassis with lugs and jumpered the riveted ground lugs to them.

Next is getting into the bandswitch with something to clean the contacts, etc. Other than the bandswitch, there just isn't that much in the Osc section used on the BC band! Should be a no brainer, but I've not found it yet. This is probably one of those things that will hit me like the snake I didn't see all along. Just wish it would hurry up and bite!

Thanks!
Brian

[w5ami]

Found the problem! Misplaced wire from A10 (on band switch) to lug 1 on the Osc coil. It should have been placed on lug #3 of the coil. Boy, what odd things can happen with one wire. It came alive better than I expected it to! Sensitive and not bad on selectivity.

Thanks for all the suggestions!

Brian