On Wed, 16 Feb 2005 08:33:04 -0500, Vinnie S.
wrote:

On Wed, 16 Feb 2005 08:08:36 -0500, Dave Hall wrote:

On Tue, 15 Feb 2005 13:36:32 -0600, "Chad Wahls"
wrote:


Did you see any bottom mounted caps connected to the final
transistor? If not then you might have to mount a piece of grounded
shield plate over the final or experiment with bypass caps until you
kill the oscillation. But try setting the bias first. If I remember
right, the bias for the final should be set at somewhere in the 30 -
40 mA range. I'll check the manual and give you the exact value.

Dave
"Sandbagger"

I kinda figured oscillation also. Bad bias can cause it. Make sure that's
correct. See if any one had hinkeyed around in there, Check serial
numbers, did these not use 2 different finals at different times? When
changing finals did they change drive components? Unfortunately I do not
have a schematic here to look around. Did anyone do any "coil spreading"?


I checked the factory service manual last night. They recommend
setting both the driver and final bias to 50 mA. That seems a bit
high, as the driver stages in many other radios are set around 40 mA.

My 2510 is set to factory specs and I've never added any "mods" to it,
and it doesn't oscillate.


Dave,

I do not have a RF VTVM or AF VTVM for the slignment. I do have a Tek 2235 scope
and freq counter. I am ordering a DMM. My friend told me instead of the VTVM,
use a DMM with a scope probe. That should work for critical voltages. If not
critical, I can use a scope. Does that sound right?


A DMM is not necessarily more accurate than a scope, it's just more
precise. If you need to make a voltage reading that goes out 2 decimal
places, the DMM can indicate that (even if it might be beyond its
calibrated accuracy in some cases).

A scope is nice. The TEK 2235 works well. I have one of those and it's
great for doing two tone and modulation tests. You can actually "peak"
a radio with the scope by simply tuning for tallest amplitude of the
waveform. Remember when looking at a scope that it measures in
voltage. Twice the voltage equates to about 4 times the power in
watts. So when you set for 100% modulation, I usually set the carrier
wave for two divisions in amplitude, and then 100% modulation will
increase that to 4 divisions.

A scope is also high impedance so it should not affect circuits all
that much. A scope is basically a voltmeter that displays in the time
domain, so anything you can measure with a DMM can be measured with a
scope.

I also prefer having a spectrum analyzer (I have an HP 8558). It is
real nice for checking spurious emissions and oscillations. Many times
aligning a radio by meter alone will not give the cleanest output. I
usually align with the analyzer for cleanest output.

Dave
"Sandbagger"