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Title: Alpha 76ca on am Post by: kc2etm 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 Title: Re: Alpha 76ca on am Post by: w4bfs 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
Title: Re: Alpha 76ca on am Post by: kc2etm 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
Title: Re: Alpha 76ca on am Post by: w4bfs 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 ...
Title: Re: Alpha 76ca on am Post by: kc2etm 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
Title: Re: Alpha 76ca on am Post by: W3RSW 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? AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
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