[Amps] Transfer capacitance, was GI-46B Question

[Traian]

jeff millar wrote:

> Art...
>
> Let's put this back on the reflector...it's getting interesting.
>
> All the data sheet from the gda.pl site list values like
> input C 10 pF
> output C .05 pF
> Transfer C 5 pF
>
> But the data sheets at nd2x.net generally look like
> input C 10 pF
> output C 5 pF
> Transfer C .05 pF
>
> Note the swapping of values between ouput C and Transfer C values
>
> Going to the Eimac web site and looking at the 8877 data sheet clears
> this up. The values swap around between grounded grid and grounded
> cathode. Feedthrough and Transfer C measure the same thing.
>

Hi Jeff,

You are right. It is a well known confusion.
>From an engineering point of view, the data sheet shall specify the
capacitances between the tube's electrodes (G-C, G-A, A-C) which
are absolute values, and not input/output ones which are relative to
the device use (or amp configuration, GG or G driven).

The input/output C are specified for devices that are intended for
a particular use (GG for this case), these devices being phisically
build to facilitate that arrangement (electrode and connections shape
and placement, shielding), and their sockets also. That recommended
mode of use shall be specified also as being the one for which the
C were measured. All these for ease of design and use.
Anyway, if will look at the data sheet for GI7 or 46, the tubes are
not specified nor recommended for a particular mode of use,
even if is easy to see that they are intended for GG applications.
So, it can cause confusion, unless you are looking very carefully
at the specs values.

There were made UHF/SHF bipolar transistors for common base
applications, some even having the base connected to their case.
I have some russian made ones.
Usually their C are specified as C between the electrodes, not
for in/out.


Have a nice weekend,
73,
Traian