[R-390] Tube microphonics & performance

[Flowertime01 at wmconnect.com]

George,

On a bad day you run what you got.
You can use them, HOWEVER.

Noise is noise.

Try them, they may be better than what you have running right now.
Then again they may not be better. 

Never turn down a tube. You can always use them as part of your test set.

If you are not using your line output, you could drop one in that side of the 
audio deck.

The microphonic per say will not hurt the radio. It may add noise to the 
signal.

If its the difference between radio and no radio, run them. 
Always run the best tubes you have.

You can compare tubes by hanging a dB meter on the audio output with a 600 
ohm 1 watt resistor and comparing tubes with each other when plugged into the 
same socket. A signal generator is easier to work with than the cal tone and 
bfo. Most AC meters have a dB scale on them. Hit a few web pages and see how to 
use your meters AC scale or dB scale. Exact numbers are not required for tube 
comparison. You are just grading what you have from good to poor. Put the best 
ones forward in the receiver and use the best of what you have.

Hang an AC volt meter across your audio output. The line level meter works 
but a volt meter will help you with tubes that are real close together. Set the 
receiver to cal and BFO off. observe the meter reading. Turn the BFO on. 
Observe the meter reading. How many dB difference did you get between BFO on and 
BFO off.

Now change a tube into one socket.

Repeat the test for that tube.

Did the second tube give you more or less dB difference?

Plug all your spare like tubes in the same socket and compare them.

After test put the worst of the bunch into the receiver.

Now retest all of the type you have that is not needed to populate the 
receiver.
Grade all of these from most dB difference to least dB difference.

Now put the best of these into the receiver.

Save the old poor ones for future testing.

Do this for each tube type.

Do the dual triode 5814's twice. Pick a socket where you know which side of 
the triode is being tested. Use the detecter socket for one side.

This is a quick post. If Its not clear to any one pop me back some mail and 
I'll try to get some more detail.

Roger KC6TRU