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 51 
 on: Today at 09:11:05 AM 
Started by NZ4Z - Last post by NN4F
i use a galvanized fence pole, about 4ft, u bolted to the tower, i did have a pulley, but switched that out for just a regular oval carabiner sort of connection using a good coated nylon rope, I had problems with the cable coming off the pulley and going down the edge of the pulley wheel, therefore jamming it all up, luckily its a crank down tower so was easy to fix, no problems since i took the pulley wheel out of the equation...

Paul - NN4F

 52 
 on: Today at 09:07:19 AM 
Started by K4EZD - Last post by AA4PB
Thanks Jim. I first entered the ham radio ranks in the late 1950's so I was looking at Extra the way it was when I first knew it. I didn't realize that there was an even earlier Extra class license.

I got my second radiotelephone commercial license at 16 and my first with ships radar endorsement at 18. The second got me a job as a radio maintenance tech with an air transport company and they encouraged me to get the first and ships radar with a pay raise  Wink So, the tests aren't all that difficult to master. I was lucky though that I had a friend who owned a TV repair business and had many years of experience so I got plenty of "hands on" experience in my early years.


 53 
 on: Today at 09:04:27 AM 
Started by KB1WSY - Last post by N2EY
A question for Jim, Peter and the other Elmers. I take it you are persuaded by the ARRL book's argument that the 6C4 needs to run a relatively low plate voltage (200V, according to the schematic) in order to avoid oscillator instability and damage to the crystals? I must admit that until I read that bit about damaging the crystals, I was so-so about the idea of messing around with the existing dropper resistor. After all, the TX is working fine, and the tone is very nice -- I am dubious about whether there is any chirp at all, for instance.

Yes. Not that there's a guarantee of crystal damage, but why take a chance?

Note too that the 5763 is probably being overdriven if the 6C4 plate voltage is too high. (I would not change the 5763 grid resistor, either).

The logical first step is to try Jim's voltage divider solution. Reading his excellent explanation, I was able to understand it, although I could never have come up with the detailed current/wattage calculations on my own.

You would, with a little practice.

As for the other solutions:
--Zeners have been used by other modern builders of this circuit, but mainly because they were having serious stability/chirp issues, often caused by using "modern," much thinner quartz crystals.
--There's really not much room on that chassis for a couple of regulator tubes and it would ruin the "museum reproduction" aspect.

Also probably unnecessary overall. BTW, I would never put VR tubes under a chassis - the glow is too pretty!

Concerning the 5763, as I understand it Peter, the issue is not with the plate voltage, which is currently well within spec, but the screen voltage, which is slightly over-spec at 260V (spec is 250) and greatly above the suggested ARRL voltage -- 195V, to "prevent excessive dissipation." I view this issue as much less important than the oscillator question. The worst thing that might happen, presumably, is that I could blow the 5763 (very unlikely?) and this tube type is still widely available. However, while I'm in there, I might as well go ahead and replace R5 with a somewhat higher value. The current value is 6.8K. We are aiming for more like 200V and we must avoid screen dissipation in excess of the maximum value of 15ma (from the RCA book) and perhaps aim more for the "typical" value of around 7ma. I tried doing the calculations but ended up tying myself in knots. What value should I try, and does it need to be a beefier power rating than the existing 1W? Surely not, screens don't take much current?  

The 5763 screen voltage is quite important. Remember that the transmitter was designed for a particular set of operating conditions, which aren't necessarily those in the tube book.

We can figure out what the new resistor should be, easily enough.

In the original design, the supply voltage (key down) was 240 and the screen voltage 195. So the 6800 ohm resistor dropped the voltage 45 volts. Dividing 45 by 6800 we get .0066 amp - 6.6 mA.

In the version you built, the supply voltage is (key down) is 290 and we want the same screen voltage as originally - 195. So the resistor must drop 95 volts at 6.6 mA. 95 divided by .0066 gives is 14,394 ohms - 15 K or 12 K should be fine.

95 time .0066 is .627 watt, so a 1 watt or preferably 2 watt is adequate.

Ironically, if I hadn't measured those voltages, I would have been none the wiser and the TX is probably just fine as it is. Knowledge is a dangerous thing! (1968 Novice Ham probably didn't have a VTVM and maybe not even a VOM, and nowhere in the instructions does ARRL suggest measuring the voltages against the schematic ... that was my idea, silly me.)

1968 ham probably had lower line voltage and such. Plus in 1968 one could get all the FT-243s, custom ground to desired frequency, for $3 each, new. Surplus cost even less.

It never hurts to check.

For TR control I recommend a simple switch or a relay.

73 de Jim, N2EY
Logistically, I'm thinking that once the three 15K bleeders are removed, there will be room to build the V1 voltage divider on the power supply terminal strip -- and then run a wire from the center of the divider network, to V1. This would be much easier than trying to cram the resistors into the area around the tube socket, and would remove a source of heat from that area. Finally, I could "remove" the old R2 simply by cutting it off with wire snippers, which is much easier than un-soldering and re-soldering new resistors.

As you can see, there should be plenty of room on the PS strip once the bleeders are gone:



I need to order a few parts to carry out these modifications (voltage divider on V1 and larger dropper on V2), so there will be a time lag before we find out the result.

73 de Martin, KB1WSY

[/quote]

 54 
 on: Today at 09:00:48 AM 
Started by N8FNR - Last post by N8FNR
Very interesting article about the Spratly Islands.

http://www.cnn.com/interactive/2014/07/world/south-china-sea-dispute/index.html?hpt=hp_c2

Zack
N8FNR

 55 
 on: Today at 08:56:16 AM 
Started by N8BBB - Last post by N4UFO
Just saw this in the classifieds... http://www.eham.net/classifieds/detail/444092

 56 
 on: Today at 08:47:56 AM 
Started by KB1WSY - Last post by KB1WSY
String some this wire - 24 gauge - out of the window to a support as high as you can get it. For insulators, use old dark plastic trouser buttons - they can't be seen so easily. For a ground, hopefully you have metal water pipes. Then use a simple parallel tuned circuit antenna tuner: use 1.5 pF of capacity per metre of wavelength, tap the tx about 2 turns up the coil and the antenna half way, tune for maximum volts on the antenna (put a small neon lamp near the antenna, or a small flashlamp bulb tapped across one or two feet of antenna lead in.) Don't worry about SWR.....

Sounds like a good backup plan but I've already got the ingredients for a monoband, 40m inverted-vee and tentative landlord approval. Easy to build. Trickiest bit is getting the coax underneath the flagstone path that's right outside the shack window, to reach the tree that will be the center support. Haven't broached that with the landlord yet, but you can rent special tools that will bore a small hole in the soil underneath a tiled path or even underneath a sidewalk. The coax has to be buried otherwise it will be in the most visible part of the landscaped garden. The other tricky bit is the lightning protection. We have violent summer storms here and will need to drive a ground rod and put in a lightning arrestor. None of these things are particularly hard but they take a bit of time.

If all this is too hard, I will use a simpler system where the antenna is basically a wire temporarily strung into a tree, and reeled in after each session of QSOs. There's a "Par EndFedz" model that would be suitable for that.

BTW, you have got some arrangement in mind to switch the antenna between tx and rx, don't you?

Not yet. Three options:

(1) Use a separate receive antenna, just a long wire. (This is the option advocated in "How to Become a Radio Amateur.")

(2) A simple rotary or knife switch.

(3) My favorite option, the electronic T/R switch from "Understanding Amateur Radio" (1963). It's a very simple one-tube circuit, although one needs to be build it carefully to avoid generating RFI/harmonics. It's a one-weekend project. Full QSK!

73 de Martin, KB1WSY

 57 
 on: Today at 08:45:54 AM 
Started by BOOTYMONSTER - Last post by MARCONI390
i find it amazing that my dumb CB antenna has generated more views and more post than any other topic in the homebrew section  Grin


BM, how about a report on how your antenna is working out.

 58 
 on: Today at 08:36:01 AM 
Started by M3OCX - Last post by G3RZP
'2QB,

5 bucks! Did you gold plate it? Some scrounging around the local Old Timers should get enough free parts to do it for nothing!

 59 
 on: Today at 08:33:31 AM 
Started by KB1WSY - Last post by G3RZP
The grid leak for the 5763 is lower (R3, 10k) is lower than the recommended 18k. I would go for 15k with a 3k3 in series and a 0.01 mFd disc ceramic across the 3k3. Then you can determine the 5763 grid current. Then play with the 6C4 plate potential to get about 5 to 5.5volts DC across the 3k3 - use the lowest plate potential that will give you that with the lowest activity crystal.

Then play with the 5763 screen dropper to get 250 volts on the screen....

As far as an antenna is concerned..........

String some this wire - 24 gauge - out of the window to a support as high as you can get it. For insulators, use old dark plastic trouser buttons - they can't be seen so easily. For a ground, hopefully you have metal water pipes. Then use a simple parallel tuned circuit antenna tuner: use 1.5 pF of capacity per metre of wavelength, tap the tx about 2 turns up the coil and the antenna half way, tune for maximum volts on the antenna (put a small neon lamp near the antenna, or a small flashlamp bulb tapped across one or two feet of antenna lead in.) Don't worry about SWR.....

BTW, you have got some arrangement in mind to switch the antenna between tx and rx, don't you?

 60 
 on: Today at 08:30:22 AM 
Started by KG9SF - Last post by KB2FCV
I see plenty of amps out there running Eimac, plenty run Russian tubes and plenty run Chinese tubes... you can't tell the difference on the receiving end. Run whatever makes you happy Smiley

One of my amps has chinese 572b in it.. and another has an eimac 8877... both work just fine and dandy..

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