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Post by Deleted on Aug 23, 2008 7:30:11 GMT -5
Dave, I just recapped one of these. Did not need restoration. Radio is in near mint condition. Still need a couple lamps. Anyway, I got great audio reports with this thing. But the local ragchew channel is 32. How do I get channel 32? I do not need any other channel up above 23, other than 32. You did tell me already, but cannot find that email.
Also, I want to turn the deadkey back a little, as it's turned up to 5 watts. Not sure how to do that on a tube rig.
Thanks !
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Sandbagger
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Post by Sandbagger on Aug 23, 2008 9:41:42 GMT -5
Dave, I just recapped one of these. Did not need restoration. Radio is in near mint condition. Still need a couple lamps. Anyway, I got great audio reports with this thing. But the local ragchew channel is 32. How do I get channel 32? I do not need any other channel up above 23, other than 32. You did tell me already, but cannot find that email. Also, I want to turn the deadkey back a little, as it's turned up to 5 watts. Not sure how to do that on a tube rig. Thanks ! Those old tube rigs were designed to put out bout 3.5 watts, so if your is putting out 5 watts (as was my Comstat when I got it), chances are that someone jumped out the plate dropping resistor which is marked R79 on the schematic. It should be a 1K resistor, and if it's jumped out, just remove the jumper and you'll be back to 3.5 watts with more punchy modulation. If you want an even lower dead key, you can change the value of that resistor to a higher value to get the dead key value to what you want. Also you can change the value of C84 across that resistor to a higher value (10 uF) to couple more audio to the final, sort of like what they do with a "swing kit". As for channel 32, you need to change a crystal. You'll need a frequency of 23.640 to give you 31,32,33,and 35 (skips 34 due to RC gap). You can either wire a switch to an existing crystal or just replace it if you never use a set of lower channels. It doesn't matter which one.
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Post by Deleted on Aug 23, 2008 13:30:33 GMT -5
Does it matter which crystal I replace, and where can I get one? I have some scrap 23 and 40's laying around.
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Sandbagger
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Post by Sandbagger on Aug 23, 2008 14:19:56 GMT -5
Does it matter which crystal I replace, and where can I get one? I have some scrap 23 and 40's laying around. No, it doesn't matter which crystal you replace, but you most likely won't find the frequency you need in a junk box. Practically all 40 channel radios were PLL (The Tram D201a was a notable exception), so you probably won't find it that way. You can, however order one from a crystal company (like Jan, international etc.). But you'll probably pay more for the crystal than what you paid for the radio.......
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Post by Deleted on Aug 23, 2008 17:51:56 GMT -5
I did a google, and nothing came up under thar crystal. So I sent am email to Jan requesting prices.
I also have to replace some lamps. I usualy use high luminous LEDs. However, I noticed that the modulation light is a neon bulb. When I think neon, I think AC. So I measured the voltage, and got both AC and DC. When I input a signal into the mic, the AC voltage goes up to 50 VAC. I suppose that rules out an LED.
Secondly, I noticed the DK started out at 5 watts, but if you hold the mic keyed down, it starts to drop in a linear manner. I held the mic down at least 20 seconds (maybe longer), and it almost went down to 3 watts. Is this normal for a tube?
Lastly, I did check R79, and it is not jumpered. Still, DK is high going to 5, then slowly drops.
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Post by Tombstone (R.I.P.) on Aug 24, 2008 8:10:28 GMT -5
A tube that slowly drops like that is called a soft tube and it probably needs replaced.
Tombstone
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Post by Deleted on Aug 24, 2008 8:40:35 GMT -5
It take longer than 20 seconds, but it does drop. Will replace it.
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Sandbagger
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Post by Sandbagger on Aug 24, 2008 9:26:49 GMT -5
I did a google, and nothing came up under thar crystal. So I sent am email to Jan requesting prices. I also have to replace some lamps. I usualy use high luminous LEDs. However, I noticed that the modulation light is a neon bulb. When I think neon, I think AC. So I measured the voltage, and got both AC and DC. When I input a signal into the mic, the AC voltage goes up to 50 VAC. I suppose that rules out an LED. Secondly, I noticed the DK started out at 5 watts, but if you hold the mic keyed down, it starts to drop in a linear manner. I held the mic down at least 20 seconds (maybe longer), and it almost went down to 3 watts. Is this normal for a tube? Lastly, I did check R79, and it is not jumpered. Still, DK is high going to 5, then slowly drops. Couple of things, be careful when replacing the bulbs with LEDS. Many times the lamps are run straight from the A.C. on the filament winding of the power transformer. The neon bulb is capacitively coupled from the plate of the modulator tube. You could probably figure out a way to substitute a LED to do the job, but you'll have to chan ge values to lower the peak voltage to the LED. Probably not worth the effort, especially if you want to kep it as original as possible. I'm bothered by the high dead key on that radio. It's possible that the slow drop in power is a soft tube, but that makes the high initial power even more difficult to believe. Is the value of R79 1K ohms? It's possible that you are transmitting spurious output and that is showing up as additional power on your wattmeter. The only way to verify that is with a spectrum analyzer though. Of course your watt meter may be a little off too. Those radios typically ran from 3 to 4 watts dead key power normally, and close to 6 watts with R79 jumped. With R79 jumped, you'd be hard pressed to get more than about 85% modulation though, which seemed like a good trade off in the 70's when everyone was focused on dead key power. It should do 100% in the stock form.
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Post by Deleted on Aug 24, 2008 10:01:28 GMT -5
I only replace bulbs with LEDs in low DC voltage applications. This particular bulb is the only neon, and you are right. Not worth the effort. I will use one of those radio shack neons.
As far as the DK, I will jumper the resistor, and get back to you with the reslts. My meter is a Diamond SX-200 meter made for all the ham bands, that I picked up at HRO. Seems to do nicely on power measurements. I will have to test it against a Bird or so.
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Post by Deleted on Aug 24, 2008 11:13:23 GMT -5
Dave, I let the unit warm up about 15 minutes. The unit is DK 4-4.5 watts unjumpered, and about 5.5 watts jumpered.
I kept the mic keyed for 1 minute, and the DK dropped gradually to 3.5 watts, and seemed to level off there.
So I am assuming this is operating normally. I do wish the DK is 3.5 watts all the time, as I sometimes run a stinger in high noise conditions, to talk to locals. 4-4.5 is too high. Can I lower it another way?
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Sandbagger
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Post by Sandbagger on Aug 24, 2008 12:31:03 GMT -5
Dave, I let the unit warm up about 15 minutes. The unit is DK 4-4.5 watts unjumpered, and about 5.5 watts jumpered. I kept the mic keyed for 1 minute, and the DK dropped gradually to 3.5 watts, and seemed to level off there. So I am assuming this is operating normally. I do wish the DK is 3.5 watts all the time, as I sometimes run a stinger in high noise conditions, to talk to locals. 4-4.5 is too high. Can I lower it another way? Sure, you can increase the value of R79. Changing it to 1.5K (use a 5 watt wirewound) should drop it down somewhere between 2 and 3 watts.
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Post by crazybob on Oct 6, 2008 10:19:42 GMT -5
I'll look around my stuff to see if I have a 23.640. I have a bunch of old crystals that came from Cloud Nine's radio shop in Glassboro, NJ.
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Post by Deleted on Oct 6, 2008 21:38:16 GMT -5
Great. I am in Swedesboro. Thanks !
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Post by crazybob on Oct 7, 2008 19:30:45 GMT -5
I started looking. the closest one I found so far was a 23.680MHz. .. I go right through your town when I take the Commodore Barry Bridge.
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Post by Deleted on Oct 7, 2008 21:23:27 GMT -5
I am on the southern side. I frequently take the bridge.
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