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Author Topic: Start Small, or Go All the Way?  (Read 5361 times)
W1QJ
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Posts: 1485




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« Reply #30 on: March 01, 2013, 04:28:55 AM »

You can get a good full output medical pull for about $350.00 cheaper than a pair of 3-500 tubes.  There are many reputable people who sell tested 8877 pulls and you are assured of getting a good one or else send it back.

Do you have any links for this? I've looked but not found those prices anywhere.

Well I have not bought one in a while and the medical pulls are getting a bit harder to find, but there was a guy on ebay selling them with a BIN for like $350.00 with a warranty that the tube will be good or send it back for another.  Now perhaps with them not ebing as readily available that price may have risen some.  But like everything else, like gas, the price moves a bit.  But considering the price of a new tube a pull for anything less than say $450.00 is still ao a bargain.  The Al-1500 has a good grid protection citcuit.  In fact so good, it will piss you off the first week you use the amp unteill you learn how to load it up withpout tripping it.  AND... most of the external anode tubes do not get gassy like glas tubes.  They getter with only filament voltage, so if you want to getter your own 8877, then just remove the plate cap and let it stay for 12 hours with just filament running.  if it does not getter then, throw it away. You are more likely to have an 8877 work perfectly after sitting for 15 years than 3-500's.  PLUS..I would buy a used Al-1500 from someone who is honest and will show you it works.  That will save you the price of an imported brand new tube.,  SO you can buy a new imported tube with the difference and now you have 2 tubes.  That should last you a lifetime if you are about 50 to 60 years old. 
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N4CR
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Posts: 1688




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« Reply #31 on: March 01, 2013, 04:35:20 AM »

I bought a used AL-1500 a couple of weeks back at the Orlando Hamcation, I don't know the conditions the tube has been presented with. So far it seems to have full output on 40 and 20, but doesn't on 15 and I also notice that the load control is always to the left of the suggested point, so it may have a bad cap in the tuning circuit.

I can get over 2kw into a dummy load on 20 and 40, but 15 seems to stop at 600 watts. I haven't cut the green wire yet. The green wire is factory intact at this point. I'll cut it next time I have the cover off.

In any case, a spare tube would be nice.
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73 de N4CR, Phil

Never believe an atom. They make up everything.
W1QJ
Member

Posts: 1485




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« Reply #32 on: March 01, 2013, 06:23:57 AM »

On 15m there are no padding capacitors involved.  SO that can't be the problem with the low power.  The green wire needs to simply be cut off ground and that is the 10m mod.  How is the swr looking in on 15m?  If you can get full power on 20 you should be able to on 15m.  You may just be hitting the wrong settings on the load and tune.  Check to make sure that the caps are zeroed with the indicators full mesh/full open.  Depending on the load perhaps the setting are different.  I only concern myself with the power output, and where it's happy it's happy.  I see no reason why all the other bands are full and not 15m.  Either input swr or wrong tune and load settings.  Play around with it.
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W1VT
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Posts: 860




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« Reply #33 on: March 01, 2013, 06:55:29 AM »

With a grounded grid amplifier, both the anode and cathode circuits need to work for proper tuning. They are in series. You may have an issue in the input, rather than the output.  

Zack W1VT
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NA0AA
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Posts: 1042




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« Reply #34 on: March 01, 2013, 04:19:03 PM »

My choice was not to go legal limit so as to avoid having to upgrade my entire station and antenna array.  I chose an AL-80B - at full output it's only 1.5 dB down from legal limit, and I can buy several replacement tubes before I approach the cost of a legal limit amp.

Whatever you do buy, I agree that 811 and 572's are not worth considering, a 3-500Z is the only current production glass tube I think worth investing in.

I have a friend who loves used Alpha/ETA amps, he no doubt would suggest you find one with a current production tube set if you wanted to go legal limit.



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N4CR
Member

Posts: 1688




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« Reply #35 on: March 01, 2013, 11:07:11 PM »

On 15m there are no padding capacitors involved.  SO that can't be the problem with the low power.

I'll start a thread on this. No point in polluting this one.
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73 de N4CR, Phil

Never believe an atom. They make up everything.
W6UV
Member

Posts: 540




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« Reply #36 on: March 02, 2013, 10:04:32 AM »

Thanks for all the suggestions and advice. I'll take the AL-811H off my list and go with something with a 3-500Z as a minimum (AL-80B). I'll also take a look at other manufacturers.

I've been doing a total rebuild of my station in the last few months and I've done everything with full legal power in mind. All of the coax is Buryflex and I've replaced the stock baluns on the beams with 4KW units. I don't have 240V in the shack yet, but plan to have an electrician pull a 240V 20A line soon.
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