[R-390] Carriers on 2 an 3 Mhz band

[Claudio Spiritelli]

Dear all,

I just reassemble my  refurbishing job on a 390A ( second one).
It looks like most thinks are working properly, and the one that do not,
they  have a good reason not to do so ( such as a broken mechanical filter,
or a missing BFO).

But  there is one problem that I can not figure it out.
On the band of 2 and 3 Mhz, I have  very high  carriers signal every 50 KHz
. I can only get those if I have an antenna connected , otherwise I do not
get any signal at all ( and the Diode load level is showing accordingly to
this fact).

When I disconnect the antenna, I do have a large oscillation signal
 several volts on a scope) on  test point E208  only on the 2 and 3 Mhz
band. When I do connect the antenna, the oscillation disappears but I have
carriers every 50 KHz.( obviously RF stage is very unstable).

I checked visually V201 and all looks ok,  I change the bypass capacitor
C227 but the problem is still there ( the modification with 47 pf in
parallel is there). I am kind of suspicious about the ground connection of
pin 7 of V201 ( as well as pin 3, they both are connected to the center of
the tube socket),  it shows grounded with the meter, but I can not see were
it goes to ground ( unless the socket center is grounded  by default), but
it be grounded since it is obvious that this receiver had a long working
life.

Does anybody have an idea were I should look to resolve the problem ( I do
not have yet a spare 6DC6 tube to try) and eliminate those  carriers that
make the 2 bands unusable?

Thanks
CS





Claudio Spiritelli

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