admiral: Admiral 7T15 cuts in and out on lower AM

Hello fellow virus fighters, hope you are all doing well.

I am working on an Admiral 7T15/5K1 radio that will lose and regain reception on the bottom half of the AM dial. The details are as follows: I can tune to stations above the middle of the dial without any problems at all. The lower half of the dial below 860 kc is difficult to lock on to a station but when I do it is loud and clear. The problem is the slightest tap or movement of the radio will kick it off the station and will also kick it back on.

I can just tap my finger on the table the radio is sitting on and it will go back to the tuned station or it will lose the station by doing the same thing. Does any one know why this is happening?

The radio has had the electrolytics C9a and C9b replaced by the previous owner with two 100 mf capacitors. There is no hum so I'm good with leaving them as is. The paper capacitors look untouched with no signs of leaking wax or rupture. Will change these if they may be the problem.

The two IF transformers/coils have electrical tape on the wires , so I think they may have been tampered with.

I look forward to hearing anyone's wisdom on the subject.

Best regards,

Vince Cappuccitti

 

To thank the Author because you find the post helpful or well done.

Dear Vince,

I don’t think that any static component is involved. It seems to me, the tuning capacitor must be the source of such a problem. Either the bearing is loose, some plates are loose or the rotor plates come in contact with something below 860KHz. That’s where I'd look first.

Regards,

Rolf

To thank the Author because you find the post helpful or well done.

Dear Rolf,

I have spent a lot of time looking at the tuning capacitor since I also thought it would be the logical place to find the problem. The bearings are good as well as the spacing between the rotor and stator. I have also unsoldered and resoldered the antennae wire and 12SA7 wire from it with out any change.

It may be something else. What would be the next thing to check?

I will go online and learn more about tuning capacitors to see if there's something I missed.

Thank you for your response.

To thank the Author because you find the post helpful or well done.

Dear Rolf, you were correct, one of the rotor plates was in contact with a stator plate. I used a continuity tester and finally found the problem. A slight bend with a knife blade put it back to the correct position.

The radio works fine now. Finally I can put it back together.

Thank you for your guidance.

Regards,

Vince

To thank the Author because you find the post helpful or well done.