[Boatanchors] A couple more questions

[Chris Howard]

Hi, Chris again.  Still working on that big homebrew AM transmitter.

I have a couple more questions for any and all who care to weigh in.

1)  The PA uses two 250TH tubes in push-pull.  There are two filament
transformers, one is a potted type and one is not.  The potted one is
leaking gunk.  I believe I have another unpotted one I could swap in
there.  The transformers are both connected to the same AC supply input
and their outputs are also joined.  If I replace the gunky one, do I
have to be careful not to get the new one wired up in an out-of-phase
situation?

2) The Bias supply produces -100 volts DC.  Also on the bias supply
there is a relay which turns on a little panel light.  Even though I am
getting the -100 volts that I think I should, the relay is not lighting
the light.  Schematic in pdf format is available here:
http://users.frii.com/yipyap/twiki/bin/view/Main/BiasSupply
The relay coil seems to be good, as tested with a 6 volt battery.
I've attempted to clean the contacts.  Otherwise, I can't figure out
what is wrong with it.

3) When I am able to get the exciter excited, it produces about 20 watts
of output.  Routing that into the PA, my grid current indicator still
says nil.  The PA is a grid driven design.  Maybe I've got my grid
current meter wired backwards or something?  I will have to watch real
closely and see if it is doing the pin-to-the-left thing.  It seems to
me that having grid bias and having RF input I should see some grid
current, assuming I get the grid input tuned right. No?
PA schematic is available here:
http://users.frii.com/yipyap/twiki/bin/view/Main/PowerAmplifier

If I get the PA meters to show some grid current, I think my next step
is try neutralization.  I have some old handbooks that describe it.

Oh, one last thing.

4) One of the PA controls, a grid inductance bandswitch,  uses a Millen
right-angle drive.  Unfortunately for me, I've stripped most of the
teeth off of one of the bevel gears in that thing.  Any good ideas on
where to get another gear or another right angle drive?  Shaft size
looks like 1/4 inch.  If not,  I may
think about rerouting that function to a panel mounted wafer switch.
If grid input is only a couple hundred volts and 20 watts of RF, I don't
think it will require anything massive.  (The nice thing about this not
being a "classing" boatanchor is that I can rebuild it any way I see
fit.)

Thanks!

Chris Howard
w0ep