Yes, the 9v battery is bias on the switching mosfet.  Lasts virtually same as shelf life.

Phil C. Sr.
k4dpk

K4POZ sells an amplifier keying interface that is the simplest of all to use.  Plug in one wire from the radio, plug in one wire from the amplifier, and you're done.

It doesn't require external power.

It doesn't care what the keying line polarity , current or voltage is.

You can find it at www.k4poz.com
'
Phil C. Sr.
k4dpk

Makes really great antenna wire.  The insulation protects the wire, and facilitates soldering if you want to make changes later on.  The wire will be untarnished under the insulation.

If you're worried about stretching, you can pre-stretch it.  Tie it to a tree, the other end to the car trailer hitch, etc. and stretch it about 3-4 percent. 

I've been using this stuff close to sixty years and have never had any of it break.

BTW....10 ga wire is fine.  A little heavier, but it may have slightly more bandwidth.

Phil C. Sr.

To me, it sounds almost certainly like a capacitor heating up and changing value.

Since the change can be corrected by a small variation in plate tank tuning, it will probably either be the plate blocking capacitor (as Pete mentioned) or one of the fixed padding capacitors to ground across one of the pi-net variables.

Phil C. Sr.
k4dpk

If there's nothing wrong with it, don't mess with it.

Phil C. Sr.
k4dpk

Just thinking....

I think most of the time (with a 3-500 amp) when these symptoms appear, it's a shorted tube, but I recall a Drake amp I repaired once that was different.  It ran a single 3-500, and one of the ceramic discs that bypassed the filament transformer leads between the choke and the transformer had shorted.

Of course the result was the same, but it took a few minutes longer to find it.

Phil C. Sr.
k4dpk

Grid-cathode short.

Phil C. Sr.
k4dpk

You could, but I don't think it'll be necessary.  I think you'll see what you need in comparing the zero, 8 and 16v.

Phil C. Sr.
k4dpk

Thanks for the feedback.

Looking fwd to the results.

Phil C. Sr.
k4dpk

Wonder what happened?

Phil C. Sr.
k4dpk

Good luck!

BTW, will you be selling tickets?

Phil C. Sr.
k4dpk

If I understand this correctly, you have a thirty foot tower, with another thirty feet of mast sticking out the top for a total of sixty feet, with antennas on top.  You only have the support in the ground four feet, in clay?

That is a recipe for disaster.  If you use a ten foot piece of wood or something to support the tower, you will only be able to reach it well below the half-way point.  That will behave as a fulcrum and will multiply the upward force to extract the support out of the ground.

You need to support the tower from above.  Is there a tree nearby?

Is there some way you can approach the base with a large vehicle, and fasten or clamp the base to the bumper of the vehicle?  That sort of system would add weight to the base and (maybe) offset the forces tending to pull the base out of the clay.

I think you should consider renting a cherry picker.  

I think there is a good possibility for serious injury with the plan you have proposed.

Phil C. Sr.
k4dpk

I think you're trying to go the wrong way with the bias.

Make sure you have a good tube and your input circuit is correctly matching the exciter to the cathode load.

Then, drop the bias zener voltage, or eliminate it altogether and try driving the amp with a hundred watts or so.

Phil C. Sr.
k4dpk

BTW, the relay discussed in the previous post is usually an integral part of any manufactured amplifier, and generally installed in any homemade amp.

Phil C. Sr.
k4dpk

You asked how it is normally done.

Assume a DPDT relay.  Tie the two NC contacts together.  Tie one NO contact to the input circuit of the amp.  Tie the other NO contact to the output, usually a pi-network, of the amp.

Then tie the common pole on the input side to the coax jumper coming from the transceiver, and the common pole on the output side to the antenna.

That way, when receiving, both the input and output of the amp are disconnected, and the receiver is connected directly to the antenna.

Now, add a third set of contacts to the relay to cause a transfer from amplifier cut-off to operating bias when it is energized (transmit mode), and you're done.

Phil C. Sr.
k4dpk