[jeffgniffke]

As I align the IF at 455 I am unable to tune out a strong signal that bleeds in...unfortunately it is also present then as I go on with the other steps...and is present at different strengths across the band. Only thing I can think it is coming from one of the push button coils.
All antenna connections disconnected...

[Raleigh]

My 40-150 had all sorts of spurious signals out of place when I connected it to the 20 ft. wire I use for an antenna at my workbench. I tried to figure out why, but gave up and put the chassis back in the cabinet, connected the original loop antennas, and all those problems went away.

Is the strong signal from a local radio station? Or some other electrical noise? Hard to see how you could get a strong signal with all antenna leads disconnected, but....

Try connecting the loop to the chassis while you align, even outside of the cabinet, and see if it will behave itself. On the 40-150 there were a lot of connections to the loop on the back cover and, IIRC, to another loop inside the cabinet. I used short test leads with alligator clips to connect them all while I aligned it, and that worked out OK. I don't know if your 40-155 is the same, but it's probably similar.

[Radioroslyn]

By disconnecting the loop ant you removing the tuned circuit from the rf amp or mixer. This will allow any and all rf garbage to get into the front end of the set. That's why you'll get all sorts of spurs and overloading signals, There's no tuned circuit to block them out.
Terry

[jeffgniffke]

Thank you Terry and John.
I will hook the loop back up and see how we do.
Yes John pretty much the same as the 150 I believe just minus one tube.

[jeffgniffke]

Better for sure...but unable to pick up the 580kc tone in the broadcast band...1400 kc seems ok...any thought why the bottom end of the band would be so weak, as I understand it is naturally is it not?

[Raleigh]

Jeff, I'd set up the radio as described in the alignment instructions, with the dial at 580 and then move my signal generator frequency until I heard something.

Then adjust compensator 19 and the tuning condenser (note C) until you get the radio dial pointer to the frequency of the signal generator.

Let's say with the radio dial set at 580 you can hear a tone when the signal generator is at 700. Your dial is off, but at least you know it receives 700 KHz. Adjust compensator 19 until the radio pointer is at 700 with the signal generator tone loud and clear. Then turn both the radio and signal generator back to 580 and see if you pick a signal somewhere near there.

Alternatively, if you can pick up the 580 signal with the pointer anywhere on the radio dial, then it's a starting place to walk the pointer back to 580 using 19.

If you can't pick up any signal on the lower part of the dial, even with the pointer way off, you might have a different problem, but try this first.

By the way, be sure that the tuning pointer is placed correctly on the dial cord by turning the tuning knob all the way to the left. Check that the tuning condenser is completely closed. There is a little dash on the far left side of the dial glass that is where the pointer should be with the tuning condenser completely closed. If it isn't, slide the pointer on the dial cord until it is behind the little dash. Make sure the condenser is still closed. Then tune to 580 and try the alignment.

Did your I.F. alignment go OK with the loop connected?

[jeffgniffke]

Hi John.
The IF worked pretty well once, as you and Terry said, with the loop back in place. Still having difficulty with the low end ...580Kc tuning. I have tried moving both the signal generator freq and the tuning cap to find a mutual ground on the bottom end....I'm going to try again tomorrow. The 19 compensator does not seem to do a lot well actually 19A either really.

Any thoughts?

thanks again.

[Raleigh]

If you aren't receiving anything on the low end of the band it could be something that keeps the oscillator from working below a certain frequency. As long as you get stations (or the sig gen tone) at the upper part of the band, we know that your IF and audio sections are working. They should not be affected by the dial setting.

There is an easy way to test the oscillator, using a second radio. Set a known good radio near your 40-155, a foot or so apart. Set the 40-155 at a station you know you can receive, as low a frequency as possible. Then set the "known good" radio dial to 455 KHz above the frequency of the 40-155 and tune around there up and down a bit, slowly and carefully.

You should hear the good radio howl when the two radios are 455 KHz apart. This shows your local oscillator is working at this frequency. You might have to turn the volume down on the 40-155 and up on the good radio to hear better.

If your good radio is digital, just set it 450 above the station frequency and tune the 40-155 around a bit. It doesn't have to be on the station for this test to work, as long as your oscillator is working and the radios are 455 KHz apart.

Now, do the same thing at a frequency below where your 40-155 can receive stations (or sig gen tone), and maybe several other places low on the dial. If you hear the howl, then your oscillator is working and we go back to scratching our heads. If you don't hear the howl, then your oscillator isn't working at those frequencies, and we can try to figure out why.

If you have a spare mixer tube (detector/oscillator) try swapping them out and see what happens. If nothing changes, we have to try something else.

[Raleigh]

Hi, Jeff, I've been doing some reading on oscillator problems, and ran across a reference in Marcus and Levy about oscillators that work at higher frequencies but not lower. They say it is almost always the converter tube when that happens. So if you have a spare, it is worth trying that.

Here is the link to the book, "Elements of Radio Servicing" by Marcus and Levy, 1947

http://antiqueradios.com/archives/Elemen...h13-16.pdf Assuming you can open the file, read from the middle of page 244 where it says in bold print "Troubles Common to the Pentagrid Converter Tube".

You can download the whole book for free in 6 pdf files here: http://antiqueradios.com/archive.shtml

[jeffgniffke]

Thank you John! What interesting reading! I actually ordered the book from Amazon for $9...I do better with hard copy than online.
So I substituted a 7S7 for the 7J7 converter....I have ordered a few of 7J7. Seemed to help but now i have squeeling at some points and microphoning. I suspect a bad loctal seating on this.
I went back to the IF...very strong but i get a very strong station signal that seems to go with it and overrun everything on the dial after the IF aligning...I can hear the IF clearly but the station signal is right there with it,

[jeffgniffke]

NOS 7J7 and 7B7 already a very big difference....more so the 7J7 mixer.

[Raleigh]

Is your strong station still all over the dial?

I wasn't sure whether you were hearing a signal from a strong station while you were aligning the RF or after the IF was finished and the signal generator was disconnected. It did cross my mind if it happened while you were aligning the RF presumably without an antenna attached, maybe the signal was coming in from the signal generator.

Glad the new tubes helped.

[jeffgniffke]

John, after working with the set on and off for a few days it seems close....better than it was. Tubes replaced, especially the mixer have made a difference. But I have a few vexing issues....after aligning the RF....attempting the 1400 and 580 Kc there is an area of microphoning of the chassis and intermittent howling at different points but all seem to be situated in the middle of the band 800-1100 kc....not sure why this would be so tight to that part of the band....that and some of the strong stations appear at other places than there assigned frequency...i.e. 830 kc WCCO appears at the far end and holds some audible signal across the whole range...stronger at some points.
Bad mixer socket perhaps? Continuity seems good on it tho without grounding where there shouldn't be...
This is a nice set ...at times when it does work it sounds great....it started as a fully packed mouse nest with many capacitors and resistors gone for mouse feeding purposes...I challenge to basically rewire but the cabinet is very nice now. Would be nice to go the last mile and get it back totally in line!
Thanks John...I'm going to send this as a message as well...sorry for the duplication but would like your input on this.
Jeff

[Raleigh]

Jeff, howling at certain frequencies or between stations sounds like an RF or antenna problem. I assume you have the antenna connected at all points. Double check your wiring, including wire colors, against the schematic.

Check your loop antenna continuity from point to point. The schematic lists very small resistances in the coils, but I think you need only to check continuity.

There are a mica cap, a resistor, and a compensator attached to the loop antenna structure that is on the back panel. Do you have any way to test them? The resistor is easy, but the capacitors might need to be removed from the circuit to test them because their capacitance is so small that lead capacitance might mess up the measurement.

Check continuity at part 13, the RF coupling coil. It looks like a small paper cap, cylindrical, coated in yellowish wax, connected to the plate of the RF tube, 1232. It should be hard against the side of the chassis near the mixer tube socket. Mine didn't have any writing or number on it, which is the only way I knew it wasn't a paper cap.

OK, here is how I understand your problem. Correct me if I'm wrong. I'm thinking out loud, so to speak. You aligned the radio IF without the antenna connected. It went OK. You tried to align the dial with the antenna connected, but you heard strong stations across the dial while you were aligning the dial with the signal generator (a few loops of wire from the sig gen wrapped around a piece of wood or cardboard near the antenna.) After you finished aligning, you have a nasty stretch in the middle of the band, and some strong stations appear all across the band, so you hear them at multiple frequencies.

Question: does WCCO appear at its right place at 830 at all, or just at weird places and not at 830?

Have you tried to align your push buttons? It's really easy, and might give some instructive results, since each push button has its own oscillator coil and antenna tuning cap. The regular tuning cap (both sides), the oscillator coil, and associated components are cut out of the circuit when you switch to the push buttons, but the antenna and RF tube are not.

Try to align KFXN at 690 on button 1, WDGY at 740 on button 2, WCCO at 830 on button 3, KTNF at 950 on button 4, WCTS at 1030 on button 5, WLOL at 1330 on button 6, and KSTP at 1500 on button 7. If the push buttons tune to those stations with no bleed-over from WCCO or other strong stations, then your problem is in the components associated with the dial tuning (mixer tube, oscillator coil, tuning caps, etc.) If you have bleed-through from WCCO or howling while you are trying to tune your push buttons, then the problem is in the antenna, antenna wiring, or the RF tube and associated components.

I just noticed your zip code, Jeff. I lived for many years in zips 55104 and 55105, not more than three or four miles from you. I bought my first old radio, a 41-280, from a family in Forest Lake. It still has the old Twin Cities button labels on it.

PS. It is always possible that in rewiring the radio, something got connected wrong. Ain't no shame in double checking all connections.

[Raleigh]

One more thought. I'm assuming that you rewired and tested the IF transformers. IIRC, there are a number of rubber coated wires in those transformer cans that must be replaced or sleeved. There are also some internal mica caps and a resistor (37B, 37C, and 37D) in the 2nd IF can that should be tested and replaced if necessary.

There is a mish-mash of frequencies in the converter tube, 7J7. All of them should be filtered out except one, 455 KHz. If your IF transformers have opens or shorts, or if the internal caps and resistors are off their specified value, you won't get the filtering you need. Spurious frequencies might show up in the wrong places.

Mica capacitors don't usually go bad, but they do often enough that they are worth testing, especially if you have a problem. The trouble is that they are hard to test in the circuit because their capacitance is usually so small that the capacitance of your test leads overwhelms the measurement, assuming you have a meter that measures capacitance. You can subtract the capacitance of your leads from the measurement of the mica cap, but that isn't as accurate as one might hope.

I have a meter that I can plug capacitors into, eliminating the effect of test lead capacitance. The trick is, you have to remove the cap from the circuit to test it. Once I remove a cap to test, it is no more trouble to replace it with a modern silver-mica cap of known value. The upshot is that I replace a fair percentage of the old domino-style micas, some of which are OK, but enough of them are marginal or bad to make testing them worthwhile.