Re: 4CX250B vs Gi7B families...
- From: Ken Scharf <wa2mzeNOTTHIS@xxxxxxxxxxxxx>
- Date: Fri, 24 Feb 2006 22:28:44 -0500
MarkAren wrote:
Hi Guys,In general triodes work best in grounded grid as you then
I am contemplating building a 144MHz power amp and looking at various
options. The obvious solution is a pair of push pull 4CX250Bs.
It appears that the Gi7B and family of Triodes can provide an equally
capable solution. They appear to be much easier to cool, by something
like an Axial Papst Fan (instead of a Snail Blower). The other obvious
advantage is not having to deal with Screen voltage, regulation and
protection. The triodes also look much easier and cheaper to mount
(given the grounded grid). Finally, it seems because of the very low
inter-electrode capacitances, it is quite easy to parallel the Triodes
up as required (even at 432MHz).
So what is the down side for using these Triodes ?
Comments and observations appreciated as usual.
Regards,
Mark.
don't have to neutralize them. At 144mhz I'm not sure HOW
you would neutralize them. Triodes in GG take more drive
power than the tetrodes, so your driver stage need to be
beefier.
I'm not familiar with the tubes in question but one idea
would be to use them grid driven in push-pull with cross
over neutralization. Much easier than trying to come up
with a neutralization scheme for a single ended amplifier.
You will need less drive in this configuration, but still
more than with the tetrodes. But you will save money
on the screen supply.
Down side? Wonder what the sockets cost? At least the
4cx250's can use surplus loctal sockets. (Though the
ceramic kind are a bit hard to find, they are out there
and cheaper than REAL 4cx250 sockets.)
.
- References:
- 4CX250B vs Gi7B families...
- From: MarkAren
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