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Author Topic: Alpha 76ca on am  (Read 3503 times)
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kc2etm
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« on: May 26, 2016, 09:47:27 PM »
Hi i have an old alpha 76ca with the trio of 8874 tubes my question is how high should i set my carrier for am use on this unit

thanks
fred
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w4bfs
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more inpoot often yields more outpoot
« Reply #1 on: May 26, 2016, 10:27:52 PM »
lets see .... 8874 has gain of 20 and control grid dissipation of 5 W max and 3 shud be good to 1500W pep so 375W carrier out divided by 20 = 18.75 W drive max ... as long as the cooling system and power xfmr are up to snuff this seems to be doable ... oh yes, I believe there are toroids in the plate circuit ... they may not like an old buzzard am xmission ... I believe I would start around 200W carrier and use the ir temp gun to see how it goes .... of course you might check the owners manual n a pinch ...73
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Beefus

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to see ourselves as others see us.
It would from many blunders free us.         Robert Burns
kc2etm
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« Reply #2 on: May 27, 2016, 04:58:52 PM »
OK thanks looks good on scope up to 300 carrier but after that it starts to flat top I guess the tubes are a little soft
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w4bfs
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more inpoot often yields more outpoot
« Reply #3 on: May 27, 2016, 09:45:34 PM »
8874 are getitng scarce, as you know ... that is a 1600 V hv amp iirc .... maybe replace with GI-7 and a bit of werk ... someone must know the Alpha guru who reconfigs these ...
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Beefus

O would some power the gift give us
to see ourselves as others see us.
It would from many blunders free us.         Robert Burns
kc2etm
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« Reply #4 on: May 27, 2016, 10:29:19 PM »
scarce they are i have two spares my father has the same amp and he replaced his with a pair of 3cx800 not to much work hardest part is finding a place for the new filament transformer
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W3RSW
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Rick & "Roosevelt"
« Reply #5 on: May 28, 2016, 10:28:50 AM »
Perhaps there's room for a smaller 6.3 vac fill. Xfor in series with the existing 6.3 winding?
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RICK  *W3RSW*
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