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Author Topic: AL80B keying problem  (Read 2687 times)
K2KGF
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Posts: 8




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« on: July 24, 2013, 08:36:05 AM »

I have a 3 yr old AL80B.  Recently, when Con Ed reduces line voltage to about 112VAC [during heat wave brown-outs] the amp won't key [with any exciter: Flex, TT599, TR7].  Any thoughts?
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AA4PB
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« Reply #1 on: July 24, 2013, 08:44:40 AM »

Well, you could adjust the taps on the power transformer for a lower voltage. The problem with that is that when the brown-out is over, the voltage will be too high stressing the power supply and tubes. Personally, I just wouldn't use the amp during brown-out conditions.
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K2KGF
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« Reply #2 on: July 24, 2013, 09:30:15 AM »

Thanks for the note.  I suspected as much but I wasn't sure that a transformer tap change would be the answer.  And, I agree that selecting a new tap just for brown-outs is not a good way to go.
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K2KGF
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« Reply #3 on: July 24, 2013, 12:29:22 PM »

The line voltage increased from 112 to 114 and the amp keyed again.  I'll just have to wait the heat waves out.
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W8JX
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« Reply #4 on: July 24, 2013, 01:22:32 PM »

The line voltage increased from 112 to 114 and the amp keyed again.  I'll just have to wait the heat waves out.

I would set primary for 115v. It is not going to really overstress it when it goes to 120 or so.
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WB2WIK
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« Reply #5 on: July 24, 2013, 02:54:31 PM »

You don't have to use the internal power supply in the amp to key the relay.

I'd be tempted to re-wire it to use a separate 12Vdc wall-wart (regulated, so its output would be 12Vdc regardless of line voltage, unless it dipped below 90Vac) and then just key that.  $10 mod that should take about ten minutes.
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K2KGF
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« Reply #6 on: August 05, 2013, 11:18:07 AM »

More on the subject of resting plate voltage: do you recommend changing xformer settings to raise V(p) from 2800 to 3000/3100??
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KH2G
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« Reply #7 on: August 05, 2013, 05:47:26 PM »

Regarding the plate voltage - I'd not change it unless I knew my measurement was accurate (Did you have a good probe or are you using the on board meter?)  The difference isn't really worth a lot of worry.
Regards,
Dick KH2G
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K2KGF
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« Reply #8 on: August 05, 2013, 06:00:44 PM »

Just using the al80b meter, thanks.
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NO2A
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« Reply #9 on: August 05, 2013, 07:35:44 PM »

Ideally your resting hv should be 3000-3100. If it`s below 3000v you may not see full rated output from that amp. Do not exceed 3100v.
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K2KGF
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« Reply #10 on: August 06, 2013, 11:51:29 AM »

thanks to all for the advice. 
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