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

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
--

Hi Ken,

Ken Fowler wrote:

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.

thanks for all suggestions, I'll check the voltages on the grids first of all,
even if capacitors should be ok, all tests I made showed no leaks on them, but
I didn't test *all* of them as some are difficult to reach.
I haven't been able to find either a DC voltage chart or an RMS signal chart
for this receiver, so I guess it won't be an easy troubleshooting.

73
Frank IZ8DWF

On Sun, 18 Dec 2011 00:23:24 +0000, Ken Fowler wrote:



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.
73. Ken, KO6NO

A better reason to inject the signal at the grid is that if you couple a
signal generator to the plate, it will detune the IF transformer and
prevent getting an accurate alignment. Using grid injection insures that
the plate circuit is unchanged from the way it will be in normal
operation.

The general rule is that connecting test equipment ALWAYS disturbs a
circuit. You want to connect it in such a way that the disturbance can
be ignored.

A burned out resistor could be the result of a bad tube but more likely
would be caused by a shorted bypass capacitor. Since the resistor
decreased in value, perhaps it applied enough current to the capacitor to
cause it to burn open (metalized type capacitors are designed to do
this), which is why you don't see a short now. It could also be the
result of a loose wire touching something, a stray solder blob from a
previous repair job, or anything like this.

Good luck,

--
Jim Mueller

To get my real email address, replace wrongname with dadoheadman.
Then replace nospam with fastmail. Lastly, replace com with us.

On Sun, 18 Dec 2011 09:23:09 +0000, frank wrote:

Hi Ken,

Ken Fowler wrote:

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.

thanks for all suggestions, I'll check the voltages on the grids first
of all, even if capacitors should be ok, all tests I made showed no
leaks on them, but I didn't test *all* of them as some are difficult to
reach. I haven't been able to find either a DC voltage chart or an RMS
signal chart for this receiver, so I guess it won't be an easy
troubleshooting.

Count on just about every stage amplifying, at least a bit. If you
inject a signal at the correct frequency someplace, it should come out
down stream, only bigger (assuming it's not so big that AGC is knocking
it down).

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com