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Author Topic: Which amp to start with?  (Read 46817 times)
KB1SNJ
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Posts: 139




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« Reply #45 on: January 16, 2017, 09:04:37 PM »

just a quick update, just ordered six #43 toroids (61mm) and two of the #52 toroids (60mm) which seemed around the 2.4" mentioned.

what is a good quality source for RG58 i will need to wind these?
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VE3TMT
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« Reply #46 on: January 17, 2017, 04:28:11 AM »

Plug n Play verticals like that promise a lot actually deliver less and can have common mode RFI issues too by nature. And such a tall vertical is not going to have favorable lobes on 20m and above too.

I worked the world with 100w and my R7 at 15'
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W8JX
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« Reply #47 on: January 17, 2017, 04:52:15 AM »

Plug n Play verticals like that promise a lot actually deliver less and can have common mode RFI issues too by nature. And such a tall vertical is not going to have favorable lobes on 20m and above too.

I worked the world with 100w and my R7 at 15'

A R7 is consider a resonate antenna as it does no need a tuner. A simple mast with a 9 to 1 and a tuner is not the same. Plus a 50 foot vertical will have unfavorable lobes on 20 and above. THose all band verticals look great in ads but do not perform well real world on all bands. Nothing magic about them.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
N3DT
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« Reply #48 on: January 17, 2017, 06:10:19 AM »

Verticals, all you have to do is model one using your ground. They're fine if you live over salt water, but not if you have regular mountain dirt. Here's a modeled 40M GP at the same height as my 40M dipole. Which would you rather use?

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N3DT
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« Reply #49 on: January 17, 2017, 07:06:22 AM »

I would seriously suggest RG400. Item 182283610795 ebay. 10' for $20. I forget how much it takes to wind a choke, but it takes a few feet. You'll never have to worry about it again.
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W8JX
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« Reply #50 on: January 17, 2017, 07:49:58 AM »

I would seriously suggest RG400. Item 182283610795 ebay. 10' for $20. I forget how much it takes to wind a choke, but it takes a few feet. You'll never have to worry about it again.

I would use RG142. It uses a copper clad solid center conductor and weighs slightly less and would work nicely wrapping in a coil and easier to find and is a mil spec cable too. RG 400 is a little more flexible but both are fairly rugged with a PFTE dielectric and will handle legal limit with ease. We used a LOT of RG142 n aircraft in flight test. We also used its big brother RG 393.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
KB1SNJ
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Posts: 139




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« Reply #51 on: January 17, 2017, 11:35:52 AM »

I have RG58 coming because thats what the chart chokes were tested with. I also bought a small amount of MilSpec RG400 to cover that base.

Is the 58 more likely to fail in some way (such as at higher power 600watts etc)?

As to the radiation pattern above, was that made in EZNEC or something else? Is there a free option thats easy to use for basic radiation pattern modeling? My property will require every tool available to develop a workable antenna.

As to that graph, the dipole is obviously way more efficient but i only have 40ft of width if the broadside is to be facing west. If I angle it southwest which may be better from here, then maybe I could get close to 50ft, and would need to erect support posts at the property line on each side, any recommendations on what to use? My house is about 15ft high at the ridge. Such  a scheme would put the horizontal right over my attic with all the network, hdmi, speaker, and house wiring everywhere. Same as when I had the G5RV above the roof.
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KB1SNJ
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« Reply #52 on: January 17, 2017, 12:11:16 PM »

oops I misspoke, the RG58u is MilsPec Belden# 8262 RG58C/U 50 Ohm Copper Mil-Spec Cable Bulk

made offer on small length RG400, awaiting reply on that.
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W8JX
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« Reply #53 on: January 17, 2017, 01:35:22 PM »

I have RG58 coming because thats what the chart chokes were tested with. I also bought a small amount of MilSpec RG400 to cover that base.

Either 400 or 142 would of worked as it is same size coax.

Is the 58 more likely to fail in some way (such as at higher power 600watts etc)?

You would not want to run a KW key down like RTTY with it. SSB would be fine. RG142 and 400 have a teflon dielectric and are better for winding chokes because closely wound coax gets much warmer with power than a single free run and 142 and 400 can handle 200c (almost 400F) without damage and therefore could easily handle a KW key down on HF.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
VK3BL
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« Reply #54 on: January 17, 2017, 05:20:33 PM »

You would not want to run a KW key down like RTTY with it. SSB would be fine. RG142 and 400 have a teflon dielectric and are better for winding chokes because closely wound coax gets much warmer with power than a single free run and 142 and 400 can handle 200c (almost 400F) without damage and therefore could easily handle a KW key down on HF.

The only way to truly answer the question is to do the math.

You need to know your load SWR, and the cable specifications.

In my practical experience RG-58 & LMR-195 are both completely fine for over 1kW keydown into a resonant load. 

Put it this way, I stopped the test because both my dummy load and amplifier were getting quite hot, but the core and the cable had next to no heating.

Having checked the specifications, the RG-58 Chris has ordered is rated to 1400 Volts - well more than enough for a Kw into a decent SWR load.
« Last Edit: January 17, 2017, 05:24:03 PM by VK3BL » Logged

J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
N3DT
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Posts: 1784




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« Reply #55 on: January 17, 2017, 07:35:27 PM »

I was really only suggesting the 400 because of the teflon and the silver plated mesh. It's much easier to work with than 58 when soldering with a big iron, which is usually needed, at least the way I do it. The 58 will melt in a heart beat. That's all.
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VK3BL
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« Reply #56 on: January 17, 2017, 07:39:31 PM »

I was really only suggesting the 400 because of the teflon and the silver plated mesh. It's much easier to work with than 58 when soldering with a big iron, which is usually needed, at least the way I do it. The 58 will melt in a heart beat. That's all.

The RG-400 is a better option for sure.  If you can get your hands on it easily, use it! Smiley
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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
W8JX
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« Reply #57 on: January 18, 2017, 04:17:34 AM »


Having checked the specifications, the RG-58 Chris has ordered is rated to 1400 Volts - well more than enough for a Kw into a decent SWR load.


The voltage rating limiting factor only for very high SWR not on a reasonably resonant load. (1 kw is just a little over 200v in a 50 ohm load) Conductor/cable size and its attenuation is limit here. I like smaller cables but 58 is too small for a balun that will see 1 kw or more high duty cycles. The core may be slow to heat because of its mass but it will heat over time and get quite warm and cable even warmer over time and cool very slowly due to limited surface are for its thermal mass. What 58 can safely handle long term in a single run vs in a tight coil is a different matter completely.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
VK3BL
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Posts: 1790


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« Reply #58 on: January 18, 2017, 04:42:30 PM »

The voltage rating limiting factor only for very high SWR not on a reasonably resonant load. (1 kw is just a little over 200v in a 50 ohm load) Conductor/cable size and its attenuation is limit here. I like smaller cables but 58 is too small for a balun that will see 1 kw or more high duty cycles. The core may be slow to heat because of its mass but it will heat over time and get quite warm and cable even warmer over time and cool very slowly due to limited surface are for its thermal mass. What 58 can safely handle long term in a single run vs in a tight coil is a different matter completely.

Agreed.

The difference is however, I have actually tested this exact configuration. 

As previously stated, I ran 1.2Kw through the balun into a Bird 8201, and the only things to get hot enough to warrant ending the test were my AL-572 & Bird 8201.

Bear in mind the Balun in question is a common mode choke NOT a transformer.  There is only ever core heating IF the balun has to choke off excessive common mode current. 

On the off chance you do blow up a core or melt the coax, its an indication that your antenna system is not suited to the band you wish to use, not an indication of the balun not handling enough power.

If you don't believe me, try for yourself.  FT240-43 cores are cheap, and RG-58 even cheaper.
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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
KH6AQ
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« Reply #59 on: January 19, 2017, 11:52:27 AM »

Does the AL-811 push the tubes beyond their limits?

The amp is rated for 500 watts OOK CW with an efficiency of 65%. During CW keying the total average plate dissipation is 135 watts for 45 watts per tube. The CCS rating of the plate is 45 watts. The ICAS is 65 watts.

The average plate current and average grid current are within the tube CCS ratings. The parameter that is high is the plate voltage. It is rated for 1250V CCS and 1500V ICAS. According to W8JI the tube cooling is adequate and the envelope and seal temperatures are ok.

Looking at the RCA datasheet we see that for class AB2 SSB the AL-811 output of 200 watts per tube is below the is midway between the maximum CCS rating of 165 watts and the ICAS rating of 235 watts.  

http://www.g8wrb.org/data///RCA/811.pdf

How about the RTTy rating of each amp. AL-811 is 400 watts while the AL-80B is 500 watts.

How about eham reviews? The AL-811, and the AL-80B both score 4.5.

I'm thinking that most of the 811A failures are due to tune up abuse. That is, not adhering to the 5 second ON, 15 second cooling period or not using a pecker or CW dits for tuning.
« Last Edit: January 19, 2017, 12:06:05 PM by WX7G » Logged
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