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Ken Fowler · December 18th 11, 01:23 AM posted to rec.radio.amateur.boatanchors

On 17-Dec-2011, wrote:

Hi all,

I'm repairing an Geloso G.4/214 receiver of a friend. I first checked
almost
all the passive components (resistor, capacitor) for value tollerance and

leakage and replaced the failed ones. Today I powered it up and started
to
check for other problems.
The receiver is quite deaf, a -40 dBm signal is barely audible on all
bands.
AM and USB work but LSB seems not working.
First of all I wanted to follow the align procedures
as stated on "Bollettino Tecnico n.85". Now I confess I don't work very
often with tube equipments, but the first phase of alignment requires to
inject a signal to the "control grid" of V4 (6BE6, second converter).
The
6BE6 datasheet mention a mixer grid (n. 1), screen grids (n.2 and 4) and
mixer grid (n. 3). Looking at the schematic, I can see that as I'd
expect,
the screen grids are connected to a fixed voltage, the first grid (mixer)
is
connected to the xtal oscillators and this leaves the third grid which is
connected with the output of the first converter (another 6BE6).
Now, what I don't understand is why I should inject a 467 KHz signal in a
place where there should be a signal at the first IF frequency (around
4.6 MHz). I'd like an explanation about this and also any other hint
in checking and aligning this receiver.
By the way, the resistor supplying anodic voltage to V3 (first converter)

was burned and measured only 90 ohm instead of 2.2 kohm as per schematic.
Does this necessarily mean I have a bad 6BE6 on V3?

Thanks in advance and best 73 de

Frank IZ8DWF

Hi Frank,

The reason that it suggests to inject the 467 KHz IF signal into the mixer
grid is that the tube will serve as a capacitive coupling for the signal
into the IF amplifier. If you try to inject at the mixer plate, you have to
worry about the high voltage at that point. If you can hear an output with
the signal injected into the mixer grid, the IF amplifier is working. Then
you can inject the 4.6 MHz signal to see if the mixer is working. If the
second mixer is working, move back to the grid of the first mixer with the
4.6 MHz signal. Etc. Etc. Of course, it would help to know what level of
signal at these points should cause a normal output. Good Luck and watch
out for those plate voltages. In fact, it is not a bad idea to check the
DC voltage on the control grids. If the voltage is positive, it might mean
a leaky coupling capactior.

73. Ken, KO6NO
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