Tomm:
If it was your first, given your gain requirement (1500w out for 50w in
or 14.8 dB !), I would recommend an 8877 in grounded grid. That tube
should provide 13 - 15 dB of gain depending on tube and bias.
There is an excellent 8877 design by W8ZR in the 21st ed of the "Radio
Handbook" by Bill Orr, W6SAI )late 70's edition).
I modified a Henry 3K over to an 8877 and was very pleased with the
performance, especially the gain. One disadvantage of the 8877 is the
relatively long warm-up, about 3 minutes. It has a reputation for a
fragile grid, but is much more indestructible than is given credit (ask
Rich, AG6K). I limited the current on mine with a trip circuit to less
than 125 ma with a fairly slow time constant, on the order of 200 ms. I
never lost a tube to grid failure, and used the 8877 for 16 years. I
popped the grid current relay a few times due to mis-tuning, but never
lost the tube. The Henry 4K, Alpha 77D and SX (pair), and Ameritron
AL-1500 use the 8877.
The other tube to consider is a 3cx1200, which is very rugged, has quick
warm-up, but a little less gain, 11 - 13 dB. But, it is excellent as a
grounded-grid choice. The Ameritron AL-1200 and Henry 3K Ultra use this
tube.
A pair of 4cx800s is worth considering, but the power supply will be more
complicated adding a screen supply and commensurate protection. The QRO
HF2500DX, Alphas 91 and 99, and ACOMs use this tube.
Good luck with the project,
73, Steve K0SF
On Thu, 20 Jan 2005 03:58:09 +0000 Tomm Aldridge <KD7QAE@ARRL.NET>
writes:
> Learned listmates,
>
> I want to embark on building my first HF tube amplifier. I would
> like
> to know what to start with, GG triode or Grid Driven Tetrode. I am
>
> looking for legal limit plus and will provide 230V for operation.
> GS35b
> tubes have caught my eye as have GU84b units but I am open to
> suggestions. Oh, and this will be a deskside unit with a 19" rack
> as
> its basis and it will be expected to provide service from 160m to
> 6m.
> Lots of great material out there on both flavors. I am looking for
>
> reliable operation, ruggedness (tolerance of my errors), 50 to 100W
>
> drive from my Kenwood to full output, simplicity and cost
> effectiveness.
>
> I am an experienced EE with PSU and systems experience but have not
> ever
> tackled a tube amp below 10GHz (grin).
>
> Waiting for all teh great guidance.
>
> KD7QAE
>
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