813 AM project problem

[kw7y]

I am building a 15 meter 2 x 813 class C final. HV is 2200V. With 16mA grid drive I can comfortably get 400W (and more) out.

Every thing works fine until I insert the Mod transformer secondary in the HV lead to the PA. NOTHING is connected to the input (audio) side of the transformer. When I apply drive to the PA my High Voltage connectors arc over. It seems this must be caused by some sort of inductive spike. Any suggestions?

- Paul

[KA2DZT]

Load down the primary of the mod xfmr with some resistors.

[kw7y]

Are you suggesting the problem I am seeing is normal, and that it will go away once I connect the modulator tubes to the transformer primary?

- Paul

[N2DTS]

2200 volts is over what you are supposed to run them at, 2000 volts and 200 ma a tube, with 15 ma grid drive each I think its supposed to be for 813's.
Not that they can not take 2200 volts most likely.


Its a very BAD idea to put 2200 volts on one side of the mod transformer and nothing on the other side.
I have a VERY nice door stop from doing just that at 2000 volts.

Mod iron is getting hard to find, do not run full power tests on one, do not put voltage on one side only, isolate from ground, do not push them with high voltage.

[W3RSW]

Hopefully you haven't toasted the xformer.
If you want to continue testing with no modulator tubes and circuit preceeding, then simply short the mod. Xfor secondary.  (Before any HV is applied. )

There is a reason, of course, because of the tremendous magnetic engage and collapse voltage spike transients developed without proper loads on either winding.

Most dual purpose AM/CW  xmitters have a shorting relay for this purpose.  Remember that any such relays or shorting switches must have adequate voltage and insulating rating.