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Author Topic: Alpha 78  (Read 1311 times)
IK0PRG
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Posts: 4




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« on: May 05, 2005, 06:33:50 AM »

Hi OM!
I have recently purchased a used ETO ALPHA 78 amplifier: it work fine and I am satisfied. I have only a little problem. It is a "F" (suffix) model so don't put out the full power on 10M. I check in the elctrical diagram and found that the C34 capacitor on S1-B Load Capacitance switch is not installed on "F" models. Do anyone know the value and working voltage of C34?
Another question. How much is the max power output of this amplifier? I need this info to value the actual life time of the tubes. Note that my amplifier haven't the "low drive mods" on board. How much the power output would be increse with the "low drive mod"?
Thank you for your reply.
73 de Roberto IK0PRG
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K6AER
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Posts: 3514




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« Reply #1 on: May 05, 2005, 03:34:06 PM »

Typically HF amplifiers put out less power on 10 meters than the lower frequencies. Power reduction could be as much as 15% lower on ten meters than 20 meters. This is because of stray inductance in the tank coil increases losses at ten meters.

For a specific legacy question send a E-Mail to Alpha Service at: service@alpaharadioproducts.com.
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W9GB
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Posts: 2622




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« Reply #2 on: May 06, 2005, 09:32:43 PM »

Roberto -

Let's deal with your other questions about the Alpha 78.
http://www.alpharadioproducts.com/legacy.asp

IF operate this amplfier PROPERLY the 8874 tubes will give years / decades of amatuer service!!
I have the Alpha 76PA, which similar to your amplifier -- but with out the "pre-set" tuning additions.  This amplifier was purchased around 1980 by one of my elmers - K9EWJ(sk).  It still has the original Eimac 3CX400A7 (8874) tubes -- and they are still operating at full output.

When this amplfier was built (1980s) "Legal Limit" as defined by the USA FCC was 1 KW DC INPUT (2 KW PEP INPUT).

You may have received an ampflier that was used heavily for government/military or contest usage -- in that case -- your tubes may be showing some age.  The 3CX400A7 (8874) tube are used in health care/medical and comemrcial trasnmitters - so a surplus market does exist.  New tubes are available from both Eimac and Svetlana.

w9gb
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W9GB
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Posts: 2622




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« Reply #3 on: May 06, 2005, 09:39:13 PM »

You may find this download of interest
Service/info manual for the ETO Alpha 76 amplifier
(much of this also covers the Alpha 76, 76A, 374A & 78 )
http://www.qsl.net/kk5dr/ETO76PDF.htm

w9gb
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