On 5/21/2011 9:15 PM, Joe Subich, W4TV wrote:
> > With respect to the 8874. At first I was under the impression that
> > the 8874 and the 3cx800a7 were interchangeable except for the heater
> > voltage, the 8874 being 6.3 and the 3cx800 being 13.5.
>
> Not by a long shot! The 8874 is also known as a 3CX400A7 it is rated
> for only *half* the plate dissipation as the 3CX800A7. The 3CX800A7
> also has significantly higher input capacitance in grounded grid.
>
> I would not even consider replacing the 3CX800A7 with a 3CX400A7.
But going the other direction except for the filament voltage the 3CX800
is a drop in replacement for the 8874/3CX400.
many an Alpha 76 series has been converted to a pair of either the
3CX800 or 3CPX800
OTOH there is no place for the filament transformer, but if the filter
caps are changed to the new ones you can reorganize enough for one to
fit as they don't take a lot of power. Of course if going with the
3CPX800s you can get a new, higher voltage plate transformer with a
filament winding already on it...However THEN you are likely to need to
redo the cap and rectifier stack for the higher DC voltage. Not a big
thing and not all that expensive.
73
Roger (K8RI)
> 73,
>
> ... Joe, W4TV
>
>
> On 5/21/2011 8:51 PM, Paul Decker wrote:
>>
>> Thanks for the input, it's really helpful.
>>
>>
>>
>> With respect to the 8874. At first I was under the impression that the 8874
>> and the 3cx800a7 were interchangeable except for the heater voltage, the
>> 8874 being 6.3 and the 3cx800 being 13.5. When I checked the data sheet to
>> make sure I noticed the absolute max voltage of the eimac 8874 listed as
>> 2200 VDC with a working voltage of 2000, while the absolute max on the
>> 3cx800 is listed as 3500 with a working voltage of 2250.
>>
>>
>>
>> So...they don't seem to be completely drop in replacements of each other, at
>> least going from the "big one" to the little one, but man they sure look the
>> same on the outside!
>>
>>
>>
>> I was talking with another ham today who is also tube knowledgeable and he
>> thought the same as I, that they were completely interchangeable save the
>> heater.
>>
>>
>>
>> Am I being paranoid here, should I just go with the full PS rather than
>> putting in the buck transformer?
>>
>>
>>
>>
>>
>> Paul
>>
>>
>>
>> ------------------------------
>>
>> Date: Sat, 21 May 2011 08:26:58 EDT
>> From: TexasRF@aol.com
>> Subject: Re: [Amps] 3cx400A7 and 8877
>> To: kg7hf@comcast.net, amps@contesting.com
>> Message-ID:<5c583.2effd26f.3b090992@aol.com>
>> Content-Type: text/plain; charset="US-ASCII"
>>
>>
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