Hi Wolfgang,
Everything you describe suggests, exactly as you said, that it is
poorly conducting relay contacts that are causing the attenuation in the
receive signal path And there are only three relays it could be; the vacuum
relay or K1 or K3 on the input board. The fact that the receive signal
restores whenever you turn the power off is a really big clue that the
problem is K3 on the Input Board.
If you look at the input board schematic you can see that there are
two bypass relays. One for T/R and QSK service and one for power off
bypass. Apparently K1 the power off bypass relay contacts are working fine,
but the contacts on K3 the QSK bypass relay are not. This could be as
simple as dirty contacts on K3, or there is also the possibility that Q4 on
the Control Board is not turning on fully and providing enough current to
the K3 coil to properly close the contacts. So perhaps Q4 or the chip that
drives it, U2 are weak. Maybe R24 is failing.
I suggest probing around on the Control board to see what the voltages
in transmit and receive mode are at U2, Q4 and Q5. The circuitry at Q4 and
Q5 are similar even though they drive different kinds of relays. Maybe you
will find the voltage on the base of Q4 does not go quite as high as the
voltage on Q5.
Good luck,
Ken N6KB
On Tue, Mar 7, 2023 at 7:51 AM Wolfgang Peringer <dk7cy@bingo-ev.de> wrote:
> Hello:
>
> I have a problem with my hercules II. When switching from transmit to
> receive there is a loss of sensitivity. The problem is intermittent.
> Keying the amp a couple of times the sensitivity returns. Problem exists
> with keying via VOX relay and also with QSK mode. Switching the
> amplifier off brings the sensitivity back at once. I think there is a
> problem with a contminated contact in one of the relays in receive. The
> Kilovac K41C vacuum relay in the output was o.k. After instaling a new
> relay the problem still exists. Maybe one of the relays on the Input
> splitter board (81430). Probably K3.
>
> Any ideas?
>
> 73
>
> Wolfgang
>
> dk7cy
>
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