In article ,
flipper wrote:
On Wed, 27 Jun 2012 22:06:46 -0500, John Byrns
wrote:
In article ,
flipper wrote:
For this application I tend to think of them as almost the same thing
but am beginning to realize that the 'extra' G4 screen is probably
what gives a heptode the higher plate impedance. Is that why, despite
the 'accidental' mentioning of dual control pentode, you seem to be
adamant about heptodes, or is there another reason?
The reason I am "adamant about heptodes", if that is what you want to call
it,
is not because of the plate resistance, it is simply because I have no
familiarity at all with DC pentodes and their characteristics.
Oh, okay. Well, just saying you're not familiar with them was enough
I don't even know any DC Pentode type numbers and am not sophisticated
enough to
know that the plate resistance of a DC pentode is lower than a heptode.
Assuming the plate resistance of a DC Pentode is lower than a heptode, is
that a
bad thing?
Well, it affects plate tank Q.
But that is a good thing, as we need to keep the plate tank Q within reason to
avoid sideband clipping and provide High Fidelity audio.
6AS6, 6DT6, 6GY6, and 6888 are some of the more 'popular' ones for
broadcasters.
I am not "adamant about heptodes", in fact I don't particularly care for
grid
modulation, preferring plate modulation instead, however it is hard to
conceive
of how to build a plate modulated transmitter using only one single section
tube, leaving the heptode, or possibly the DC Pentode, as the only easy
choice
for a single tube transmitter. I do have a design for a single tube
transmitter
using your 6ME8 that meets my design brief, however it would require me to
build
my own well balanced push-pull RF antenna coupling transformer.
Yeah, a PP transformer is in some of my designs too but I'm skittish
about trying to wind one.
After a little out of the box thinking, it occurs to me that it may be possible
to make lemonade out of these lemons. It appears that by intentionally
unbalancing the transformer you can generate AM without the need for biasing the
deflectors to produce a carrier. Tight coupling between the two sections of the
winding would probably still be required to insure that no weird phase shifts
are produced which would prevent achieving 100% negative modulation. Hopefully
using a toroidal transformer core would provide adequate coupling between the
two plates?
--
Regards,
John Byrns
Surf my web pages at,
http://fmamradios.com/