Hi All,

I am contemplating the design of a class C amp for 144MHz using wound
output inductors and a split stator (butterfly) tuning cap. This seems
to be a very common approach in the good old days for QQV06-40As, but I
don't think that I have seen such a design for 250Bs in push pull.

The issue of voltage rating of the o/p cap is of course an issue, and
the output coupling loop will need to be well insulated (assume 1500VDC
on the anodes).

Any obvious reason that this isn't a common approach ?

Ian ? Anyone ??

Thanks,

Mark.

MarkAren wrote:
Hi All,


Any obvious reason that this isn't a common approach ?

Ian ? Anyone ??

Thanks,

Mark.

Yep - push pull amps make wonderful frequency multipliers. In the days
when there was nothing in use above them, it didnt matter. Now it does.

Andrew VK3BFA.

On Mon, 24 Oct 2005 00:56:14 -0700, MarkAren wrote:

Hi All,

I am contemplating the design of a class C amp for 144MHz using wound
output inductors and a split stator (butterfly) tuning cap. This seems to
be a very common approach in the good old days for QQV06-40As, but I don't
think that I have seen such a design for 250Bs in push pull.

There is a design for a 2M amp using a single 4CX250B in the old
RSGB VHF/UHF Manual. The inductor in the anode circuit is 3.5 turns
of 1/8 inch copper tube. The output coupling loop is 1 turn.

I don't see any reason why you couldn't make a push-pull
version with a pair of 250Bs.

The issue of voltage rating of the o/p cap is of course an issue, and the
output coupling loop will need to be well insulated (assume 1500VDC on the
anodes).

You can reduce the risk of frying the operator by grounding one
end of the output coupling loop.

Any obvious reason that this isn't a common approach ?

The only advantage I can see with this arrangment is a reduction
in the size of the amp. Since a 500W tube amp will require a large
power supply, I don't see much point in building a tiny PA.
A stripline amp will give greater efficiency and will only
be a little bit bigger.

73, C U on 2M. Ed. EI9GQ.

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On 24 Oct 2005 00:56:14 -0700, "MarkAren"
wrote:

Hi All,

I am contemplating the design of a class C amp for 144MHz using wound
output inductors and a split stator (butterfly) tuning cap. This seems
to be a very common approach in the good old days for QQV06-40As, but I
don't think that I have seen such a design for 250Bs in push pull.

The issue of voltage rating of the o/p cap is of course an issue, and
the output coupling loop will need to be well insulated (assume 1500VDC
on the anodes).

Any obvious reason that this isn't a common approach ?

The loaded Q (and the circulating current) of the tank will be
necessarily high because of the tube output capacitance. The
efficiency is dependent upon the loaded to unloaded Q ratio. The
tuned line approach can offer higher unloaded Q and a physically
larger structure to dissipate the heat generated by the inevitable
loss.

Output coupling will likely be problematic as well.

I ran a single tube with a wound plate inductor and the efficiency was
pretty low, but it was just a 100W driver so size was more important
than efficiency.

On 24 Oct 2005 06:54:30 -0700, "Andrew VK3BFA"
wrote:


MarkAren wrote:
Hi All,


Any obvious reason that this isn't a common approach ?

Ian ? Anyone ??

Thanks,

Mark.

Yep - push pull amps make wonderful frequency multipliers. In the days
when there was nothing in use above them, it didnt matter. Now it does.

All class C amps make pretty good frequency multipliers. If you're
worried about the -second- harmonic, then p-p is superior.

Wes Stewart wrote:
On 24 Oct 2005 06:54:30 -0700, "Andrew VK3BFA"
wrote:



All class C amps make pretty good frequency multipliers. If you're
worried about the -second- harmonic, then p-p is superior.

Tnks Wes - didnt know that one, obviously need to dig out my theory
handbooks and do some revision.