SB-301 Problems

[Bill Coleman AA4LR]

On 3/4/98 8:03 PM, Dennis Heikura at heikud at DIRECTCON.NET wrote:

>Just as
>if the
>AGC is working backwards. The rig had no AGC when first received due to a
>shorted
>AGC diode. I replaced both with garden variety silicon rectifier diodes
>of the
>proper voltage as dont have the correct Heath replacements. AGC now works
>but as above.

Are you sure you didn't install the diode backwards?

As I remember, the SB-301 had a pretty good AGC with a long hang time if
set to "Slow". Does the AGC switch make any difference.

>Secondly, receiver gets more and more insensitive as you go up in bands.
>Real hot
>on 80 and 40, then weaker on 20, weaker still on 15, and very weak on 10.

I used a used SB-301 for years as my novice rig. While it may not be as
hot as some modern rigs, it wasn't bad (not like the HR-10B I had before
it, which was completely insensitive on 10m).

I'd check the RF amp and first mixer tube. You might also want to run the
alignment procedure on the preselector coils.

However, I would fix the AGC problem first. Who knows, it may have
damaged something in the AGC chain.

>This seems
>to be common with the HW and SB rigs. Any cures? Am useing this rx with a
>Heath
>6 meter convertor which converts to the 10 meter band so greater sensitivity
>would
>be welcome.

The 6 meter convertor should have a fair amount of gain - so trememdous
sensitivity on 10m probably isn't necessary.

Question: when you switch from a 10m antenna to the 6m converter, do you
find an increase in background noise level (assuming AGC off)? If so, you
have enough gain, you don't need any more sensitivity.



Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at radio.org
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901

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