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 Post subject: Tuning on my AK-10 (4340) Seems to be "Off"
PostPosted: Mar Mon 05, 2018 2:16 am 
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Joined: Mar Mon 05, 2018 1:33 am
Posts: 3
I just (finally, after all these years) purchased an ARBE III and tried it out on an Atwater Kent Model 10 (4340) that I'd picked up a few months back. The radio receives stations, but there are two "sweet spots" on each tuning dial, depending upon where I'm trying to tune. The dial numbers should get smaller as the frequency increases, but I was copying a station on 830 in an area that should be the higher end of the band. With my sig generator tuned to around 1200 kHz, the radio picks up the signal when the dials are in the 40-50 range (or at spots higher on the dial readout).

I'm having a hard time thinking that someone incorrectly attached the knobs on all three variables.

Also, there are certain settings when the radio will go into oscillation, although backing off the gain pot typically will eliminate that problem. Actually, it's a good way to find weak stations; just listen for a heterodyne and zero beat.

Can someone shed some light on this, please?

Thanks! Rick


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 Post subject: Re: Tuning on my AK-10 (4340) Seems to be "Off"
PostPosted: Mar Tue 06, 2018 2:43 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 7948
Location: Cleona, PA
It was common until around 1930 to think of wavelength rather than frequency with regard to radio broadcasting. As you tune higher in frequency, wavelength becomes lower. That's why the dial numbers go lower as the condensers open up and pick up higher frequencies. Then around 1930 the old 0-100 logging scales gave way to actual frequency markings on radio dials when one-dial tuning with more accurate tracking became possible, especially with superhetrodynes.

Edit: Now that I re-read your post I'm confused. When your dials read 0, are the condenser plates open or closed?

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Reece


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 Post subject: Re: Tuning on my AK-10 (4340) Seems to be "Off"
PostPosted: Mar Tue 06, 2018 4:37 pm 
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Joined: Jan Mon 16, 2012 4:15 pm
Posts: 4524
Location: Near Brandon, Iowa
You might want to eliminate one of the variable elements and first quantify the radio's performance independent of the ARBE by using an RF signal generator to characterize the response of each RF amp stage over the entire range of tuning. That should give you a good picture of how well each stage tuning tracks with the other two stages. Dial number tracking won't be perfect (if it was, A-K would have gone to single-knob tuning long before they did) but it should be fairly close. If one of the three tuning modules is far out of bed with the other two, it is probably damaged- perhaps shorted turns on the RF transformer coil or corrosion that affects the unit's resonance point.

I don't know much about the ARBE but it is probably producing harmonics in addition to the desired output frequency, and your old A-K may be reacting to these. Maybe someone here has bothered to do a spectrum analysis on this transmitter.

Your Model 10 is a straight TRF set without regeneration, so if it is oscillating that would seem to point to a signal feedback path that shouldn't be there. Possibly inductive coupling between gain stages (or between two stages) due to wire dress or component placement?


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 Post subject: Re: Tuning on my AK-10 (4340) Seems to be "Off"
PostPosted: Mar Tue 06, 2018 6:39 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 33215
Location: Maryland 20709, USA
The three RF transformers on the 4340 are all oriented with their axes vertical.
That creates interstage coupling and definitely promotes feedback aka oscillation.
The only way to stop it is to reduce the gain (filament voltage).

Later breadboards and cabinet sets had their coils oriented orthogonally.
That minimized coupling.

- Leigh

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http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


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 Post subject: Re: Tuning on my AK-10 (4340) Seems to be "Off"
PostPosted: Mar Tue 06, 2018 11:45 pm 
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Joined: Mar Mon 05, 2018 1:33 am
Posts: 3
Thanks for the helpful hints. After thinking about this for a bit (always dangerous), I have concluded that someone must have removed the tuning knobs--perhaps to clean them for a better auction presentation--and didn't bother trying to get them correctly oriented when they were re-installed.

I have reset them to where I think they should be, although without opening each capacitor enclosure, I can't know for certain when the plates are fully meshed. The way it's now set, stations on the high end of the band are on the zero end of the dial (shorter wavelength, smaller number). I'm also now seeing the shadow signal on the blank side of the dial, which is where it should be.

I'm getting readings that compare with those of some similar sets. It seems to top out at around 1200 kHz. Have not checked the lower end with the signal generator yet. Work has been busy today.

This set is in very good condition overall and had 3 functional tubes, although it's accumulated a bit of dust and a very fine layer of what could be tobacco tar residue or some similar precipitate. Have seen both.

73, Rick, WW1ME


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 Post subject: Re: Tuning on my AK-10 (4340) Seems to be "Off"
PostPosted: Mar Fri 09, 2018 12:17 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1299
Location: Phoenix, Arizona
The dial calibration on your AK 10 has no relationship to wavelength or frequency. It is just so you can have a number to go back to.

Most sets of this period do not tune much above 1100, 1200 Khz. The AM band was expanded several times later. Stations used wavelength and not frequency back in the day. Some stations had to share a frequency, one in the morning, one at night.

Jim


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 Post subject: Re: Tuning on my AK-10 (4340) Seems to be "Off"
PostPosted: Mar Sun 11, 2018 3:25 am 
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Joined: Mar Mon 05, 2018 1:33 am
Posts: 3
Thanks again, all who replied.

Yes, I'm well aware of the relationship between frequency and wavelength and that the dial numbers are simply for reference but have no meaning in terms of unit of measure. On a decent antenna, I was able to hear stations during daylight hours.

I've set that one aside for the time being and have hauled a Dayton XL-25 I acquired a year or so ago off the shelf to putter with. It has a few defective components, etc, and the variable capacitors needed to be mechanically loosened up (i.e., so they would turn). Not bad shape considering its age, though.

73, Rick, WW1ME


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