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Author Topic: Al-811H low output some bands  (Read 1006 times)
N2QLT
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Posts: 43




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« on: February 06, 2019, 10:56:49 AM »

I just re-tubed this amp that I bought recently. I used 811 tubes. On 80m I'm getting 600 watts easily with 60 watts in. On 15 and 20 I'm getting only 450 watts. Tested with different meters and loads too. Same result. And that's with pushing the grid current almost to the 200ma max. Any ideas?
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MM0IMC
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Posts: 255




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« Reply #1 on: February 06, 2019, 03:15:42 PM »

Perhaps only 3 of the 4 valves (tubes) are working?  Huh
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WA2YLY
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Posts: 4




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« Reply #2 on: February 07, 2019, 02:44:46 AM »

what radio are you using as exciter?tubes sound ok on 80 mtrs.I had similiar problem after replacing tubes.Turned out the rig IC 7100 rig was seeing higher swr on some bands and cutting back on drive power.IC 7100 has built in swr meter and power output so made it easy to check this out.
bob
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N2QLT
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Posts: 43




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« Reply #3 on: February 07, 2019, 06:17:24 AM »

Using IC-751a. Will check SWR between rig and amp. Thanks!
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W4KVW
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Posts: 0




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« Reply #4 on: February 11, 2019, 10:01:53 AM »

Someone may have adjusted the pots on the rear of the amplifier since you said you purchased it used. If they have been tuned then it will result in lower output on the bands that were re-tuned. Also you may remove one tube at a time & test the amplifier output & it will operate just fine & you can then see if a tube is bad. Be very careful of the High Voltage. It will operate with just one tube at a time if you want to test each tube by itself. It is a good way to find weak or bad tubes but kind of slow as well.

Clayton
W4KVW
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KF7CG
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Posts: 1215




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« Reply #5 on: February 12, 2019, 04:28:08 AM »

I use an AL811H that I enabled 12 and 10 meters on.  Find that input tuning is a compromise between each of the bands at a particular switch setting. It could well be that the amp you have has been peaked for use with the WARC bands at the expense of the others.
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