[R-390] bad tubes? test good

[Todd, KA1KAQ]

Had the same issue with my 75A-4 years back, Russ. Decided to replace all
the weak tubes from a good stock of NOS military surplus JAN tubes. Turned
the receiver back on and it was not performing well, can't remember now
exactly what it was. After checking all the worst things I could think of,
eventually I was left with the tubes. Started swapping back the old tubes
one by one. Found  one tube - think it was a 12BA6 maybe - that was the
culprit. Stuck the weak one back in and it worked fine. Checked it in the
B&K 747 tester, it checked excellent. Great emission, no gas, no shorts.
But wouldn't work in the circuit.

At the end of the day, your radio is still the best tube tester. And some
tubes that test weak or bad in a tester will still work fine.

de Todd/'Boomer'  KA1KAQ/4

PS - W3JN is coming over tomorrow to see what kind of trouble we can find.
Might get the 40m dipole back up in the air. Fair warning....

On Sat, Feb 18, 2017 at 6:45 PM, <wb3fau55 at neo.rr.com> wrote:

> Here is my recent similar problem.  I had  just reworked an SP-600.
> Working fine.  Then, after using it  for a few days,  it starts to drift
> badly.  Put my hand near the HF osc tube, a 6C4,  it walks  even more.
> Tube tested  fine.  I pulled it, and put in a new 6C4, and added a black
> IERC tube shield,  been fine ever since.  As stated,  you cannot judge  a
> tube  by good action in a tube checker. [TV-7D]  Russ.
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