Expo kit Question

[Fdtrucker]

I got a expo 100c kit for my Grant XL on ebay. It came with instructions and chart. It says to put the provided choke in place of diode 52. One problem... It did not come with a choke. Is anyone familiar with this kit? What is a choke and where can I get one? Great thanks..

 

[nomadradio]

Uh, it's a good thing that choke didn't come with your kit. It doesn't go IN PLACE of D52. It goes in SERIES with D52. The longer of the two legs of D52 is pulled out of the hole, straightened, and lap-soldered to one leg of the choke. The choke's other lead goes in the now-empty circuit-board hole and gets soldered to the foil pad.


What the choke does is to extend the range of the clarifier. Trouble is, the range of your clarifier also gets moved downwards. Sometimes enough that it won't go up in frequency high enough to reach the normal "middle" of the channel you're on.

Typically, if the clarifier is simply converted to feed a full range from zero to 8 Volts into the thing, you'll get enough clarifier range to reach the next channel below, and fill in those "skipped" frequencies between 3 and 4, 7 and 8, 11 and 12, 15 and 16, as well as between 19 and 20.

Since the channel selector skips these frequencies on all three bands, you might find that an "upper" or "lower" channel you want is in one of those five skipped spots on the selector.

Trouble is, stretching the clarifier to cover a channel and a half (or more) makes it very touchy when trying to fine-tune a SSB signal. If all you will use is AM, this is not a big deal. If you plan to use the radio for sideband, there are other ways to fill in the skipped frequencies and still retain the "fine"-tune character of the clarifier knob. Besides, stretching the clarifier with that choke will make the radio drift a lot more with temperature changes. If you use it indoors as a base, this is probably not a problem. If the radio is used mobile, you'll be "chasing" SSB stations on the clarifier as the radio warms up in winter, or cools down in the summer while running. Leaving out the choke improves temperature stability.

Oh, the inductance value of your missing RF choke is 5.6 microhenries, typically abbreviated as "uH".

73

 

[Fdtrucker]

Thanks Nomad. I got it installed now I found out the lower frequency crystal is broke and a solder joint on the 40 ch socket is off. Gotta love ebay. I need a 11.1758 crystal now. Anyone know where to get one? 73

 

[Fdtrucker]

Ok the lower crystal is working but it drops out below ch. 22.. I can live with that as long as I have the uppers.. :beer
P.S.
I should have put this in the Tech Bench section sorry guys..

 

[nomadradio]

The "drops out below 22" issue is an alignment item. The tuning voltage that sets the radio's frequency has an upper and lower limit. The slug in tuneable coil (I think) L19 determines the range of frequencies you get between those limits. Sometimes it will cover all 132 channels top-to-bottom, but that slug will have to be set to make that happen. It's the one with the plug of beeswax covering the hole, next to the VCO module.

Some radios will stay locked into the frequency over a smaller range, maybe 100 or 110 channels total top-to-bottom. When that happens, you can contemplate how to "stretch" the tuning range of the VCO. Better to decide which 10 or 20 channels you won't care to use. The slug in L19 can be set so that the "dropout" point is at the top or at the bottom of those 135 channels, and choose whether to lose the very bottom few channels, or the top few. If the radio is used mobile, you'll find the exact channel where it "drops" will drift some with temperature changes. A radio used as a base won't encounter such a wide swing in it's operating temperature.

If the coverage it gives you now is sufficient, I'd leave it alone. If it gives you the upper channels without dropping the top few, there's no need to twiddle it. Odds are that the receiver sensitivity and transmit power are a bit wimpier at 18 or 20 channels below 1 than on channels 1-40. It will be wimpier still 44 channels below. Just making it lock onto the channel all the way down to 26.515 won't also get you full power and receiver sensitivity down there. Making the radio perform over a wider span than about 80 channels will require some realignment, not just the VCO slug. Seems to me Lou Franklin posted some (free) info on broadbanding this kind of radio, but I can't remember where.

Making the radio perform over a span of channels three times as far as the original design gave you will involve some small compromises, one way or another.

Glad to hear you got the Ebay specimen reconstructed. Makes me wonder how long until an Expo 100 kit gets as high a price as a 8950 tube?

73

 

[Fdtrucker]

Thanks Nomad. I will leave it alone. I don't really use the lower ones anyway. Just was curious if it was broke. Now I know. I found another problem with the kit. The channel list was off one number. I adjusted the screws on the kit and still couldnt get it where it was supposed to be. I made a new list out everythings cool now. Just waiting for some DX now!
73

 

[DTB Radio]

Which Expo kit (what letter) did you get? Its possible the kit was actually intended for a different model of radio, and thats why its 1 channel off. You might be able to coax the channels into the order you want by creative crystal tricks (in-series capacitors or inductors). Nomad is right on the money about the missing channels.

 

[nomadradio]

Uh, DTB if you look at the channel list that came with the older Expo kits, you'll see that it only jumps up or down 44 channels. This puts channel 1 in two places: with the selector at "40" on the lower band, and on "1" on normal channels. Likewise channel 40 shows up on the normal channels, AND as channel "1" on the upper band.

Only when the multi-band "export" radios became common did they try to "stretch" the Expo kits one more channel up and down. This made your channel digits read the same as your buddy with the Connex/Galaxy/Superstar "bandit" radio.

Newer kits made since that change appear to have the same crystals, but with capacitor values altered to pull them further up/down by one channel.

Had a bunch of "A" and "A+" kits that would not run on the lower channels, because they put a disc cap in parallel with the 14.920 crystal to pull it down to 14.910. Trouble was, the output would be low, and the crystal would not 'start' reliably when you selected lowers on the kit's switch. The fix was to remove the shunt capacitor, and insert a 5.6 uH choke in series with the lower crystal on the kit. The trimmer cap would then bring the lower-band crystal's frequency down without reducing its output level.

I think they may have revised the crystal specs on the "B", "C" and "L" kits to do this, but they did NOT on the 15.36 MHz "A" and "N" kits. They used the old "+/-44" crystal, and revised the oscillator circuit.

If you encounter an "old" Expo kit meant for only 44 up/down instead of 45, the channel list packed with it will reflect this.

The color of the Expo carton has changed over the years, but I have no record of what year any one color was used. If you knew this, I suppose you could tell by that whether it's an older "44" or the newer "45" type kit.

Once upon a time, long ago they were made by CB City International, run by Lou Franklin. Don't know when he sold it off, or to whom. The expander kits that Lou continued to offer were more sophisticated, but came with NO crystals. Not too sexy when you have to pay twenty bucks more or less each for custom-made one-at-a-time crystals.

So long as the trimmer cap brought it onto the channel, who cares how old it is? Gotta figure if it's the wrong kit, it won't be anywhere near close enough to even set a channel frequency, let alone get within one channel of correct.

73

 

[Fdtrucker]

I have the C model and the box looks old and yellow. It works good so far the first number on the upper channel is supposed to be 27.405 but it's actually 27.415 which is good becouse it does'nt duplicate channel 40 when you switch it up. The same goes for the lower ch. 40 is 26.955 and decends to ch. 22 where it drops off. There are no duplicate frequencies. It actually works better that way. Kind of like someone planned it.

 

[Switch Kit]

I realize this thread is older but was surprised I missed it , Good Thread !! , I've asked before with mixed replies , but IM taking a total guess here ? is the 5.6uh choke for the clairifer concedered a "super type diode" or is that totally something different ? Also , IM only familure with the Galaxy blue Box N kits concerning PC-122s which only give the upper channels of the given chip in the radio but I was told that the Expo type should give both uppers and lower freq's ? , I do understand that you can change the chip in the 122 to another but you will then have to have at least 5Khz of slide in your clarifier to make that chip work because it only shows the freq's in 27.400 were you need to slide for the extra 5 .For some reason or other never cared much for that idea if there were other ways of doing it in which there was. I am kind of curious though ? The Grant XL has the 8917 pll , which I find to be one of the easiest chips to convert over for upper and lower freq's , is it a better idea to use a Expo Kit rather then the chip itself ? are there advantages to this ? I realize you can use the switches on the radio for the channels if one would want to sacrafice those or just add switches to the radio for them. I was told a year or so ago that they stopped making these Expo Kits.......kind of makes it harder for some of those not so good chipped radios to have extras.but with all those 10 meter exports and the sign of the times ,I guess it won't really matter that much.